ESP32 SoC Series

Implementation for Espressif ESP32 SoC Series. More...

Detailed Description

Implementation for Espressif ESP32 SoC Series.

This document describes the RIOT implementation for supported variants (families) of Espressif's ESP32 SoC series.

Author
Gunar Schorcht gunar.nosp@m.@sch.nosp@m.orcht.nosp@m..net

RIOT-OS on ESP32 SoC Series Boards

Table of Contents

  1. Overview
  2. Short Configuration Reference
  3. ESP32x MCU
    1. Features of ESP32x SoCs
    2. Features Supported by RIOT-OS
    3. Limitations of the RIOT-port
  4. Toolchain
    1. RIOT Docker Toolchain (riotdocker)
    2. Manual Toolchain Installation
  5. Flashing the Device
    1. Toolchain Usage
    2. Compile Options
    3. Flash Modes
    4. ESP-IDF Heap Implementation
  6. Common Peripherals
    1. GPIO pins
    2. ADC Channels
    3. DAC Channels
    4. I2C Interfaces
    5. PWM Channels
    6. SPI Interfaces
    7. Timers
    8. RTT Implementation
    9. UART Interfaces
    10. CAN Interfaces
    11. Power Management
    12. Other Peripherals
  7. Special On-board Peripherals
    1. SPI RAM Modules
    2. SPIFFS Device
  8. Network Interfaces
    1. Ethernet MAC Network Interface
    2. WiFi Network Interface
    3. WiFi SoftAP Network Interface
    4. ESP-NOW Network Interface
    1. Bluetooth Interface
    2. Other Network Devices
  9. Application-Specific Configurations
    1. Make Variable CFLAGS
    2. Application-Specific Board Configuration
    3. Application-Specific Driver Configuration
  10. Debugging
    1. JTAG Debugging
    2. QEMU Mode and GDB

Overview

The RIOT port for ESP32 is an implementation of RIOT-OS for the Espressif ESP32 SoC series (hereafter called ESP32x), which supports most of the functions of RIOT-OS.

Due to the potential confusion caused by referring to the SoC series in exactly the same way as the namesaking SoC variant, we need to define a terminology in this document to distinguish between a variant and a set of variants:

Note
Variants of Espressif's ESP32 SoC Series are called ESP32x families in RIOT's terminology.

Back to table of contents

Short Configuration Reference

The following table gives a short reference of all board configuration parameters used by the RIOT port for ESP32x SoCs in alphabetical order.

Parameter Short Description Type[1]
ADC_GPIOS GPIOs that can be used as ADC channels m
CAN_TX GPIO used as CAN transceiver TX signal o
CAN_RX GPIO used as CAN transceiver RX signal o
DAC_GPIOS GPIOs that can be used as DAC channels m
I2C0_SPEED Bus speed of I2C_DEV(0) o
I2C0_SCL GPIO used as SCL for I2C_DEV(0) o
I2C0_SDA GPIO used as SCL for I2C_DEV(0 o
I2C1_SPEED Bus speed of I2C_DEV(1) o
I2C1_SCL GPIO used as SCL for I2C_DEV(1) o
I2C1_SDA GPIO used as SCL for I2C_DEV(1) o
PWM0_GPIOS GPIOs that can be used at channels of PWM_DEV(0) o
PWM1_GPIOS GPIOs that can be used at channels of PWM_DEV(1) o
PWM3_GPIOS GPIOs that can be used at channels of PWM_DEV(2) o
PWM4_GPIOS GPIOs that can be used at channels of PWM_DEV(3) o
SPI0_CTRL SPI Controller used for SPI_DEV(0), can be VSPI HSPI o
SPI0_SCK GPIO used as SCK for SPI_DEV(0) o
SPI0_MOSI GPIO used as MOSI for SPI_DEV(0) o
SPI0_MISO GPIO used as MISO for SPI_DEV(0) o
SPI0_CS0 GPIO used as default CS for SPI_DEV(0) o
SPI1_CTRL SPI Controller used for SPI_DEV(1), can be VSPI HSPI o
SPI1_SCK GPIO used as SCK for SPI_DEV(1) o
SPI1_MOSI GPIO used as MOSI for SPI_DEV(1) o
SPI1_MISO GPIO used as MISO for SPI_DEV(1) o
SPI1_CS0 GPIO used as default CS for SPI_DEV(1) o
UART1_TXD GPIO used as TxD for UART_DEV(1) o
UART1_RXD GPIO used as RxD for UART_DEV(1) o
UART2_TXD GPIO used as TxD for UART_DEV(2) o
UART2_RXD GPIO used as RxD for UART_DEV(2) o
  1. Type: m - mandatory, o - optional

The following table gives a short reference in alphabetical order of modules that can be enabled/disabled by board configurations and/or application's makefile using USEMODULE and DISABLE_MODULE.

Module Default Short description
esp_eth not used enable the Ethernet MAC (EMAC) network device
esp_gdb not used enable the compilation with debug information for debugging
esp_hw_counter not used use hardware counters for RIOT timers
esp_i2c_hw not used use the i2C hardware implementation
esp_idf_heap not used enable ESP-IDF heap implementation
esp_log_colored not used enable colored log output
esp_log_startup not used enable additional startup information
esp_log_tagged not used add additional information to the log output
esp_now not used enable the ESP-NOW network device
esp_qemu not used build QEMU for ESP32 application image
esp_spi_oct not used enable SPI RAM in Octal SPI Mode
esp_rtc_timer_32k not used use RTC timer with external 32.768 kHz crystal as RTT
esp_spi_ram not used enable SPI RAM
esp_spiffs not used enable SPIFFS for on-board flash memory
esp_wifi not used enable the Wifi network device in WPA2 personal mode
esp_wifi_ap not used enable the WiFi SoftAP network device
esp_wifi_enterprise not used enable the Wifi network device in WPA2 enterprise mode


Back to table of contents

ESP32x MCU

ESP32x SoCs are low-cost, ultra-low-power, single or dual-core SoCs from Espressif Systems with integrated WiFi and Bluetooth BLE module. The SoCs are either based on

At the moment, ESP32, ESP32-S2, ESP32-S3 and ESP32-C3 variants (families) are supported by RIOT-OS.

Note
Even if the used ESP32x SoC is a dual-core version, RIOT-OS uses only one core.

Back to table of contents

Features of ESP32x SoCs

The ESP32 SoC Series consists of different ESP32x SoC variants (families), which differ in the type and the number of processor cores used and the hardware modules supported.

Features of The ESP32 SoC variant (family)

The key features of ESP32 are:

MCU ESP32 Supported by RIOT
Vendor Espressif
Cores 1 or 2 x Tensilica Xtensa LX6 1 core
FPU ULP - Ultra low power co-processor no
RAM 520 KiB SRAM
8 KiB slow RTC SRAM
8 KiB fast RTC SRAM
yes
yes
yes
ROM 448 KiB yes
Flash 512 KiB ... 16 MiB yes
Frequency 240 MHz, 160 MHz, 80 MHz yes
Power Consumption 68 mA @ 240 MHz
44 mA @ 160 MHz (34 mA @ 160 MHz single core)
31 mA @ 80 MHz (25 mA @ 80 MHz single core)
800 uA in light sleep mode
10 uA in deep sleep mode
yes
yes
yes
yes
yes
Timers 4 x 64 bit yes
ADCs 2 x SAR-ADC with up to 18 x 12 bit channels total yes
DACs 2 x DAC with 8 bit yes
GPIOs 34 (6 are only inputs, 18 are RTC GPIOs) yes
I2Cs 2 yes
SPIs 4 yes (2)
UARTs 3 yes
WiFi IEEE 802.11 b/g/n built in yes
Bluetooth v4.2 BR/EDR and BLE yes
Ethernet MAC interface with dedicated DMA and IEEE 1588 support yes
CAN version 2.0 yes
IR up to 8 channels TX/RX no
Motor PWM 2 devices x 6 channels no
LED PWM 16 channels with 20 bit resolution in 2 channel groups with 4 timers yes
Crypto Hardware acceleration of AES, SHA-2, RSA, ECC, RNG no
Vcc 2.5 - 3.6 V
Documents Datasheet
Technical Reference


Features of The ESP32-C3 SoC variant (family)

The key features of ESP32-C3 are:

MCU ESP32-C3 Supported by RIOT
Vendor Espressif
Cores 1 32-bit RISC-V core yes
FPU - -
RAM 400 KiB SRAM
8 KiB RTC SRAM
yes
yes
ROM 384 KiB yes
Flash 8 MiB yes
Frequency 160 MHz, 80 MHz yes
Power Consumption 20 mA @ 240 MHz
15 mA @ 80 MHz
130 uA in light sleep mode
5 uA in deep sleep mode
yes
yes
yes
yes
Timers 2 x 54 bit yes
ADCs 2 x SAR-ADC with up to 6 x 12 bit channels total yes
DACs - -
GPIOs 22 yes
I2Cs 1 yes
SPIs 3 yes (1)
UARTs 2 yes
WiFi IEEE 802.11 b/g/n built in yes
Bluetooth Bluetooth 5 (LE) yes
Ethernet - -
CAN version 2.0 yes
IR up to 4 channels TX/RX -
Motor PWM - no
LED PWM 6 channels with 14 bit resolution in 1 channel group with 4 timers yes
Crypto Hardware acceleration of AES, SHA-2, RSA, ECC, RNG no
Vcc 3.0 - 3.6 V
Documents Datasheet
Technical Reference


Features of The ESP32-S2 SoC variant (family)

The key features of ESP32-S2 are:

MCU ESP32-S2 Supported by RIOT
Vendor Espressif
Cores 1 x Tensilica Xtensa LX7 1 core
FPU ULP - Ultra low power co-processor no
RAM 320 KiB SRAM
8 KiB slow RTC SRAM
8 KiB fast RTC SRAM
yes
yes
yes
ROM 128 KiB yes
Flash 512 KiB ... 32 MiB Dual/Quad/Octal SPI (external or internal) yes
Frequency 240 MHz, 160 MHz, 80 MHz yes
Power Consumption 66 mA @ 240 MHz
50 mA @ 160 MHz (40 mA @ 160 MHz single core)
33 mA @ 80 MHz (28 mA @ 80 MHz single core)
19 mA @ 40 MHz (16 mA @ 40 MHz single core)
240 uA in light sleep mode
8 uA in deep sleep mode
yes
yes
yes
yes
yes
yes
Timers 4 x 54 bit yes
ADCs 2 x SAR-ADC with up to 20 x 13 bit channels total yes
DACs 2 x DAC with 8 bit -
GPIOs 43 (22 are RTC GPIOs) yes
I2Cs 2 yes
SPIs 4 yes (2)
UARTs 2 yes
WiFi IEEE 802.11 b/g/n built in yes
Bluetooth - -
Ethernet - -
CAN version 2.0 yes
IR up to 4 channels TX/RX no
Motor PWM 2 devices x 6 channels no
LED PWM 8 channels with 14 bit resolution in 1 channel group with 4 timers yes
Crypto Hardware acceleration of AES, SHA-2, RSA, ECC, RNG no
Vcc 2.8 - 3.6 V
Documents Datasheet
Technical Reference


Features of The ESP32-S3 SoC variant (family)

The key features of ESP32-S3 are:

MCU ESP32-S3 Supported by RIOT
Vendor Espressif
Cores 2 x Tensilica Xtensa LX7 1 core
FPU ULP - Ultra low power co-processor no
RAM 512 KiB SRAM
8 KiB slow RTC SRAM
8 KiB fast RTC SRAM
yes
yes
yes
ROM 384 KiB yes
Flash 512 KiB ... 32 MiB Dual/Quad/Octal SPI (external or internal) yes
Frequency 240 MHz, 160 MHz, 80 MHz yes
Power Consumption 66 mA @ 240 MHz
50 mA @ 160 MHz (40 mA @ 160 MHz single core)
33 mA @ 80 MHz (28 mA @ 80 MHz single core)
19 mA @ 40 MHz (16 mA @ 40 MHz single core)
240 uA in light sleep mode
8 uA in deep sleep mode
yes
yes
yes
yes
yes
yes
Timers 4 x 54 bit yes
ADCs 2 x SAR-ADC with up to 20 x 12 bit channels total yes
DACs - -
GPIOs 45 (22 are RTC GPIOs) yes
I2Cs 2 yes
SPIs 4 yes (2)
UARTs 3 yes
WiFi IEEE 802.11 b/g/n built in yes
Bluetooth Bluetooth 5 (LE) yes
Ethernet - -
CAN version 2.0 yes
IR up to 8 channels TX/RX no
Motor PWM 2 devices x 6 channels no
LED PWM 8 channels with 14 bit resolution in 1 channel group with 4 timers yes
Crypto Hardware acceleration of AES, SHA-2, RSA, ECC, RNG no
Vcc 2.3 - 3.6 V
Documents Datasheet
Technical Reference


Rather than using the ESP32x SoCs directly, ESP32x boards use an ESP32x module from Espressif which integrates additionally to the SoC some key components, like SPI flash memory, SPI RAM, or crystal oscillator. Some of these components are optional.

Most common modules used by ESP32x SoC boards are:

Back to table of contents

Features Supported by RIOT-OS

The RIOT-OS for ESP32x SoCs supports the following features at the moment:

Back to table of contents

Limitations of the RIOT port

The implementation of RIOT-OS for ESP32x SoCs has the following limitations at the moment:

Back to table of contents

Toolchain

To build RIOT applications for ESP32x SoCs, the following components are required:

Principally, there are two ways to install and use the ESP32 toolchain, either

Back to table of contents

Using RIOT Docker Toolchain

The easiest way to use the ESP32 toolchain is to use the RIOT Docker build image. It is specially prepared for building RIOT applications for various platforms and already has all the required tools and packages installed. Details on how to setup Docker can be found in section Getting Started.

The building process using Docker comprises two steps:

  1. Building the RIOT application in Docker using command:
    $ sudo docker run --rm -i -t -u $UID -v $(pwd):/data/riotbuild riot/riotbuild
    riotbuild@container-id:~$ make BOARD= ...
    riotbuild@container_id:~$ exit
  2. Flashing the RIOT application on the host system using command
    $ make flash-only BOARD=...

Both steps can also be performed with a single command on the host system by setting the BUILD_IN_DOCKER variable:

$ BUILD_IN_DOCKER=1 DOCKER="sudo docker" \
make flash BOARD=...
Note
During the migration phase from the ESP32 toolchain with GCC 5.2.0, which was specially compiled for RIOT, to Espressif's precompiled ESP32 vendor toolchain with GCC 8.4.0, the RIOT Docker build image schorcht/riotbuild_esp32_espressif_gcc_8.4.0 has to be used instead of riot/riotbuild as this already contains the precompiled ESP32 vendor toolchain from Espressif while riot/riotbuild does not. Therefore, the RIOT Docker build image has to be pulled with command:
$ sudo docker pull schorcht/riotbuild_esp32_espressif_gcc_8.4.0
and the RIOT Docker build image in step 1 has to be started with command:
$ sudo docker run --rm -i -t -u $UID -v $(pwd):/data/riotbuild schorcht/riotbuild_esp32_espressif_gcc_8.4.0
The single step build command on the host system has then to be:
$ BUILD_IN_DOCKER=1 DOCKER="sudo docker" DOCKER_IMAGE=schorcht/riotbuild_esp32_espressif_gcc_8.4.0 \
make flash BOARD=...

Back to table of contents

Using Local Toolchain Installation

Prerequisites

In addition to the common tools defined in section Getting Started - Common Tools, the following tools or packages are required to install and use the ESP32 toolchain (Debian/Ubuntu package names):

Script-based installation

The shell script $RIOTBASE/dist/tools/esptools/install.sh is used to install Espressif's precompiled versions of the following tools:

$RIOTBASE defines the root directory of the RIOT repository. The shell script takes an argument that specifies which tools to download and install:

$ dist/tools/esptools/install.sh
install.sh <tool>
tool = all | esp32 | esp32c3 | esp32s2 | esp32s3 | openocd | qemu

Thus, either all tools or only certain tools can be installed.

The ESP32x tools are installed within a subdirectory of the directory specified by the environment variable $IDF_TOOLS_PATH. If the environment variable $IDF_TOOLS_PATH is not defined, $HOME/.espressif is used as default.

Using the variable IDF_TOOLS_PATH and its default value $HOME/.espressif for the toolchain installation in RIOT allows to reuse the tools that have already been installed according to the section "Get Started, Step 3. Set up the tools". if you have already used ESP-IDF directly.

Using the toolchain

Once the ESP32x tools are installed in the directory specified by the environment variable $IDF_TOOLS_PATH, the shell script $RIOTBASE/dist/tools/esptools/install.sh can be sourced to export the paths of the installed tools using again the environment variable $IDF_TOOLS_PATH.

$ . dist/tools/esptools/export.sh
Usage: export.sh <tool>
tool = all | esp32 | esp32c3 | esp32s2 | esp32s3 | openocd | qemu

All the tools required for building a RIOT application for ESP32x SoCs should then be found in the path.

Back to table of contents

Installation of the ESP32 SDK (ESP-IDF)

RIOT-OS uses the ESP-IDF, the official SDK from Espressif, as part of the build. It is downloaded as a package at build-time and there is no need to install it separately.

Installation of esptool.py (ESP flash programmer tool)

The RIOT port does not work with the esptool.py ESP flasher program available on GitHub or as a package for your OS. Instead, a modified version included in ESP-IDF SDK is required.

To avoid the installation of the complete ESP-IDF SDK, for example, because RIOT Docker build image is used for compilation, esptool.py has been extracted from the SDK and placed in RIOT's directory dist/tools/esptool. For convenience, the build system uses always the version from this directory.

Therefore, it is not necessary to install esptool.py explicitly. However esptool.py depends on pySerial which can be installed either using pip

$ sudo pip3 install pyserial

or the package manager of your OS, for example on Debian/Ubuntu systems:

$ apt install python3-serial

For more information on esptool.py, please refer to the git repository.

Back to table of contents

Flashing the Device

Toolchain Usage

Once the toolchain is installed either as RIOT docker build image or as local installation, a RIOT application can be compiled and flashed for an ESP32x boards. For that purpuse change to RIOT's root directory and execute the make command, for example:

The BOARD variable in the example specifies the generic ESP32 board that uses the ESP32-WROOM-32 module and option -C the directory of the application.

Back to table of contents

Compile Options

The compilation process can be controlled by a number of variables for the make command:

Option Values Default Description
CFLAGS string empty Override default board and driver configurations, see section Application-Specific Configurations.
FLASH_MODE dout, dio, qout, qio dout Set the flash mode, see section Flash Modes
PORT /dev/tty* /dev/ttyUSB0 Set the port for flashing the firmware.


Optional features of ESP32 can be enabled by USEMODULE definitions in the makefile of the application. These are:

Module Description
esp_eth Enable the Ethernet MAC (EMAC) interface as netdev network device, see section Ethernet Network Interface.
esp_gdb Enable the compilation with debug information for debugging with QEMU and GDB (QEMU=1) or via JTAG interface with OpenOCD.
esp_i2c_hw Use the hardware I2C implementation, see section I2C Interfaces.
esp_idf_heap Use the ESP-IDF heap implementation, see section ESP-IDF Heap Implementation.
esp_log_colored Enable colored log output, see section Log output.
esp_log_startup Enable additional startup information, see section Log output.
esp_log_tagged Add additional information to the log output, see section Log output.
esp_now Enable the built-in WiFi module with the ESP-NOW protocol as netdev network device, see section ESP-NOW Network Interface.
esp_spi_oct Enable the optional SPI RAM in Octal SPI mode, see section SPI RAM Modules.
esp_qemu Generate an application image for QEMU, see section QEMU Mode and GDB.
esp_rtc_timer_32k Enable RTC hardware timer with external 32.768 kHz crystal.
esp_spiffs Enable the optional SPIFFS drive in on-board flash memory, see section SPIFFS Device.
esp_spi_ram Enable the optional SPI RAM, see section SPI RAM Modules.
esp_wifi Enable the built-in WiFi module as netdev network device in WPA2 personal mode, see section WiFi Network Interface.
esp_wifi_ap Enable the built-in WiFi SoftAP module as netdev network device, see section WiFi SoftAP Network Interface.
esp_wifi_enterprise Enable the built-in WiFi module as netdev network device in WPA2 enterprise mode, see section WiFi Network Interface.


For example, to activate a SPIFFS drive in on-board flash memory, the makefile of application has simply to add the esp_spiffs module to USEMODULE make variable:

USEMODULE += esp_spiffs

Modules can be also be activated temporarily at the command line when calling the make command:

USEMODULE="esp_spiffs" make BOARD=...

Back to table of contents

Flash Modes

The FLASH_MODE make command variable determines the mode that is used for flash access in normal operation.

The flash mode determines whether 2 data lines (dio and dout) or 4 data lines (qio and qout) are used for flash addressing and data access. Since one GPIO is required for each data line, qio or qout increases the performance of SPI flash data transfers but uses two additional GPIOs. That means these GPIOs are not available for other purposes in qio or qout flash mode. If you can live with lower flash data transfer rates, you should always use dio or dout to keep them free for other purposes:

For more information about these flash modes, refer the documentation of esptool.py.

Note
On some modules and most boards, these additional GPIOs used in qio or qout flash mode are not broken out and therefore not available.

Back to table of contents

Log output

The RIOT port for ESP32x SoCs implements a log module with a bunch of macros to generate log output according to the interface as defined in system logging header. These macros support colored and tagged log output.

The colored log output is enabled by module esp_log_colored. If colored log output is enabled, log messages are displayed in color according to their type: Error messages are displayed in red, warnings in yellow, information messages in green and all other message types in standard color.

When the esp_log_tagged module is used, all log messages are tagged with additional information: the type of message, the system time in ms, and the module or function in which the log message is generated. For example:

I (663) [main_trampoline] main(): This is RIOT! (Version: 2019.10-devel-437-gf506a)

Either the LOG_* macros as defined in system logging header or the tagged version LOG_TAG_* of these macros can be used to produce tagged log output. If the LOG_* macros are used, the function which generates the log message is used in the tag while a tag parameter is used for the LOG_TAG_* macros. For example,

LOG_ERROR("error message");
#define LOG_ERROR(...)
log an error
Definition: log.h:92

generates a log message in which the name of the calling function is used as tag. With

LOG_TAG_ERROR("mod", "error message");

a log message with string mod in the tag is generated.

The esp_log_startup module can be used to enable additional information about the boot process, the board configuration, the system configuration, the CPU used by the system, and the available heap. These information may help to detect problems during the startup. If the application does not start as expected, this module should be used.

Back to table of contents

ESP-IDF Heap Implementation

ESP-IDF SDK provides a complex heap implementation that supports multiple heap segments in different memory areas such as DRAM, IRAM, and PSRAM. Whenever you want to use these memory areas as heap, you have to use the heap implementation from the ESP-IDF SDK. ESP-IDF heap is not used by default. To use it, it has to be enabled by the the makefile of the application:

USEMODULE += esp_heap
Note
ESP-IDF heap implementation is used by default, when the following modules are used: esp_spi_ram, esp_wifi_any

Back to table of contents

Common Peripherals

ESP32x SoCs have a lot of peripherals that are not all supported by the RIOT port. This section describes the supported peripherals and how they have to be configured.

Back to table of contents

GPIO pins

The number of GPIOs and their usage depends on the respective ESP32x SoC family. For details, see:

Back to table of contents

ADC Channels

ESP32x SoCs integrate two SAR ADCs (ADC1 and ADC2). The bit width of the ADC devices, the number of channels per device and the GPIOs that can be used as ADC channels depend on the respective ESP32x SoC family. For details, see:

ADC_GPIOS in the board-specific peripheral configuration defines the list of GPIOs that can be used as ADC channels on the board, for example:

#define ADC_GPIOS { GPIO0, GPIO2, GPIO4 }

Thereby the order of the listed GPIOs determines the mapping between the ADC lines of the RIOT and the GPIOs. The maximum number of GPIOs in the list is ADC_NUMOF_MAX. The board specific configuration of ADC_GPIOS can be overridden by Application specific configurations.

The number of defined ADC channels ADC_NUMOF is determined automatically from the ADC_GPIOS definition.

Note
As long as the GPIOs listed in ADC_GPIOS are not initialized as ADC channels with the adc_init function, they can be used for other purposes.

With the function adc_set_attenuation an attenuation of the input signal can be defined separately for each ADC channel.

int adc_set_attenuation(adc_t line, adc_atten_t atten)
Set the attenuation for the ADC line.
adc_attenuation_t
Attenuations that can be set for ADC lines.
Definition: adc_arch.h:48
uint_fast8_t adc_t
Define default ADC type identifier.
Definition: adc.h:72

This leads to different measurable maximum values for the voltage at the input. The higher the attenuation is, the higher the voltage measured at the input can be.

The attenuation can be set to 4 fixed values 0 dB, 2.5/3 dB, 6 dB and 11/12 dB, where 11 dB respectively 12 dB is the default attenuation.

Attenuation Voltage Range Symbol
0 dB 0 ... 1.1V (Vref) ADC_ATTEN_DB_0
2.5 / 3 dB 0 ... 1.5V ADC_ATTEN_DB_2_5
6 dB 0 ... 2.2V ADC_ATTEN_DB_6
11 / 12 dB 0 ... 3.3V ADC_ATTEN_DB_11 (default)


Note
The reference voltage Vref can vary from device to device in the range of 1.0V and 1.2V.

The Vref of a device can be read at a predefined GPIO with the function adc_line_vref_to_gpio. The results of the ADC input can then be adjusted accordingly.

extern int adc_line_vref_to_gpio(adc_t line, gpio_t gpio);
int adc_line_vref_to_gpio(adc_t line, gpio_t gpio)
Output reference voltage of a ADC line to GPIO n.

For the GPIO that can be used with this function, see:

Note
ADC2 is also used by the WiFi module. The GPIOs connected to ADC2 are therefore not available as ADC channels if the modules esp_wifi or esp_now are used.

Back to table of contents

DAC Channels

Some ESP32x SoCs support 2 DAC lines at predefined GPIOs, depending on the respective ESP32x SoC family. These DACs have a width of 8 bits and produce voltages in the range from 0 V to 3.3 V (VDD_A). The 16 bit DAC values given as parameter of function dac_set are down-scaled to 8 bit.

The GPIOs that can be used as DAC channels for a given board are defined by the #DAC_GPIOS macro in the board-specific peripheral configuration. The specified GPIOs in the list must match the predefined GPIOs that can be used as DAC channels on the respective ESP32x SoC.

#define DAC_GPIOS { GPIO25, GPIO26 }

This configuration can be changed by application-specific configurations.

The order of the listed GPIOs determines the mapping between the RIOT's DAC lines and the GPIOs. The maximum number of GPIOs in the list is DAC_NUMOF_MAX.

DAC_NUMOF is determined automatically from the DAC_GPIOS definition.

Note
As long as the GPIOs listed in DAC_GPIOS are not initialized as DAC channels with the dac_init function, they can be used for other purposes.

DACs are currently only supported for the ESP32 SoC variant.

Back to table of contents

I2C Interfaces

ESP32x SoCs integrate up to two I2C hardware interfaces.

The board-specific configuration of the I2C interface I2C_DEV(n) requires the definition of

I2Cn_SPEED, the bus speed for I2C_DEV(n), I2Cn_SCL, the GPIO used as SCL signal for I2C_DEV(n), and I2Cn_SDA, the GPIO used as SDA signal for I2C_DEV(n),

where n can be 0 or 1. If they are not defined, the I2C interface I2C_DEV(n) is not used, for example:

#define I2C0_SPEED I2C_SPEED_FAST
#define I2C0_SCL GPIO22
#define I2C0_SDA GPIO21
#define I2C1_SPEED I2C_SPEED_NORMAL
#define I2C1_SCL GPIO13
#define I2C1_SDA GPIO16

The board-specific pin configuration of I2C interfaces can be changed by application specific configurations by overriding the according I2Cn_* symbols.

The default configuration of I2C interfaces for ESP32x SoC boards depend on used ESP32x SoC family, for details see:

Note
  • To ensure that the I2Cn_* symbols define the configuration for I2C_DEV(n), the definition of the configuration of I2C interfaces I2C_DEV(n) must be in continuous ascending order of n. That is, if I2C_DEV(1) is used by defining the I2C1_* symbols, I2C_DEV(0) must also be used by defining the I2C0_* symbols.
  • The GPIOs listed in the configuration are only initialized as I2C signals when the periph_i2c module is used. Otherwise they are not allocated and can be used for other purposes.
  • The same configuration is used when the I2C bit-banging software implementation is used by enabling module esp_i2c_sw (default).

The number of used I2C interfaces I2C_NUMOF is determined automatically from board-specific peripheral definitions of I2C_DEV(n).

Beside the I2C hardware implementation, a I2C bit-banging protocol software implementation can be used. This implementation allows bus speeds up to 1 Mbps (#I2C_SPEED_FAST_PLUS). It can be activated by adding

USEMODULE += esp_i2c_sw

to application's makefile. The Disadvantage of the software implementation is that it uses busy waiting.

Note
The hardware implementation seems to be very poor and faulty. I2C commands in the I2C command pipeline are sporadically not executed. A number of ACK errors and timeouts caused by protocol errors are the result. The hardware implementation is recommended only if they can be tolerated. Therefore, the software implementation is used by default.

Back to table of contents

PWM Channels

The PWM peripheral driver for ESP32x SoCs uses the LED PWM Controller (LEDC) module for implementation. The LEDC module has either 1 or 2 channel groups with 6 or 8 channels each, where the first channel group comprises the low-speed channels and the second channel group comprises the high-speed channels. The difference is that changes in the configuration of the high-speed channels take effect with the next PWM cycle, while the changes in the configuration of the low-speed channels must be explicitly updated by a trigger.

The low-speed channel group always exists while the existence high-speed channel depends on respective ESP32x SoC family. For details, see:

Each channel group has 4 timers which can be used as clock source by the channels of the respective channel group. Thus it would be possible to define a maximum of 4 virtual PWM devices in RIOT per channel group with different frequencies and resolutions. However, regardless of whether the LEDC module of the ESP32x SoC has one or two channel groups, the PWM driver implementation only allows the available channels to be organized into up to 4 virtual PWM devices.

The assignment of the available channels to the virtual PWM devices is done in the board-specific peripheral configuration by defining the macros PWM0_GPIOS, PWM1_GPIOS, PWM2_GPIOS and PWM3_GPIOS These macros specify the GPIOs that are used as channels for the 4 possible virtual PWM devices PWM_DEV(0) ... PWM_DEV(3) in RIOT, for example:

#define PWM0_GPIOS { GPIO0, GPIO2, GPIO4, GPIO16, GPIO17 }
#define PWM1_GPIOS { GPIO27, GPIO32, GPIO33 }

This configuration can be changed by application-specific configurations.

The mapping of the GPIOs as channels of the available channel groups and channel group timers is organized by the driver automatically as follows:

Macro 1 Channel Group 2 Channel Groups Timer
PWM0_GPIOS LEDC_LOW_SPEED_MODE LEDC_LOW_SPEED_MODE LEDC_TIMER_0
PWM1_GPIOS LEDC_LOW_SPEED_MODE LEDC_HIGH_SPEED_MODE LEDC_TIMER_1
PWM2_GPIOS LEDC_LOW_SPEED_MODE LEDC_LOW_SPEED_MODE LEDC_TIMER_2
PWM3_GPIOS LEDC_LOW_SPEED_MODE LEDC_HIGH_SPEED_MODE LEDC_TIMER_3

For example, if the LEDC module of the ESP32x SoC has two channel groups, two virtual PWM devices with 2 x 6 (or 8) channels could be used by defining 'PWM0_GPIOS' and 'PWM1_GPIOS' with 6 (or 8) GPIOs each.

The number of used PWM devices PWM_NUMOF is determined automatically from the definition of PWM0_GPIOS, PWM1_GPIOS, PWM2_GPIOS and PWM3_GPIOS.

Note
  • The total number of channels defined for a channel group must not exceed PWM_CH_NUMOF_MAX
  • The definition of PWM0_GPIOS, PWM1_GPIOS, PWM2_GPIOS and PWM3_GPIOS can be omitted. However, to ensure that PWMn_GPIOS defines the configuration for PWM_DEV(n), the PWM channels must be defined in continuous ascending order from n. That means, if PWM1_GPIOS is defined, PWM0_GPIOS must be defined before, and so on. So a minimal configuration would define all channels by PWM0_GPIOS as PWM_DEV(0).
  • The order of the GPIOs in these macros determines the mapping between RIOT's PWM channels and the GPIOs.
  • As long as the GPIOs listed in PWM0_GPIOS, PWM1_GPIOS, PWM2_GPIOS and PWM3_GPIOS are not initialized as PWM channels with the pwm_init function, they can be used other purposes.

Back to table of contents

SPI Interfaces

ESP32x SoCs have up to four SPI controllers dependent on the specific ESP32x SoC variant (family):

The controllers SPI0 and SPI1 share the same bus signals and can only operate in memory mode on most ESP32x SoC variants. Therefore, depending on the specific ESP32x SoC family, a maximum of two SPI controllers can be used as peripheral interfaces:

In former ESP-IDF versions, SPI interfaces were identified by the alias names FSPI, HSPI and VSPI, which are sometimes also used in data sheets. These alias names have been declared obsolete in ESP-IDF.

SPI interfaces could be used in quad SPI mode, but RIOT's low level device driver doesn't support it.

The board-specific configuration of the SPI interface SPI_DEV(n) requires the definition of

where n can be 0 and 1. If they are not defined, the according SPI interface SPI_DEV(n) is not used, for example:

#define SPI0_CTRL SPI3_HOST // VSPI could also be used on ESP32 variant
#define SPI0_SCK GPIO18 // SCK signal
#define SPI0_MISO GPIO19 // MISO signal
#define SPI0_MOSI GPIO23 // MOSI signal
#define SPI0_CS0 GPIO5 // CS0 signal
#define SPI1_CTRL SPI2_HOST // HSPI could also be used here on ESP32 variant
#define SPI1_SCK GPIO14 // SCK Camera
#define SPI1_MISO GPIO12 // MISO Camera
#define SPI1_MOSI GPIO13 // MOSI Camera
#define SPI1_CS0 GPIO15 // CS0 Camera

The pin configuration of SPI interfaces can be changed by application specific configurations by overriding the according SPIn_* symbols.

The default configuration of SPI interface for ESP32x SoC boards depend on used ESP32x SoC family, for details see:

Note
  • To ensure that the SPIn_* symbols define the configuration for SPI_DEV(n), the definition of the configuration of SPI interfaces SPI_DEV(n) must be in continuous ascending order of n. That is, if SPI_DEV(1) is used by defining the SPI1_* symbols, SPI_DEV(0) must also be used by defining the SPI0_* symbols.
  • The order in which the available interfaces SPI2_HOST (alias HSPI or FSP) and SPI3_HOST (alias HSPI) are assigned doesn't matter.
  • The GPIOs listed in the configuration are only initialized as SPI signals when the periph_spi module is used. Otherwise they are not allocated and can be used for other purposes.

#SPI_NUMOF is determined automatically from the board-specific peripheral definitions of SPI_DEV(n).

Back to table of contents

Timers

There are two different implementations for hardware timers.

By default, the timer module is used. To use the counter implementation, add

USEMODULE += esp_hw_counter

to application's makefile.

The number of timers and available timer implementations depend on used ESP32x SoC family, for details see:

Timers are MCU built-in features and not board-specific. There is nothing to be configured.

Back to table of contents

RTT implementation

The RTT peripheral low-level driver provides a RTT (Real Time Timer) with a frequency of 32.768 kHz. It either uses the RTC hardware timer if an external 32.768 kHz crystal is connected to the ESP32x SoC or the PLL-controlled 64-bit microsecond system timer to emulate the RTC timer.

Whether an external 32.768 kHz crystal is connected to the ESP32x SoC is specified as a feature by the board definition using the pseudomodule esp_rtc_timer_32k. If the feature esp_rtc_timer_32k is defined but the external 32.768 kHz crystal is not recognized during startup, the PLL controlled 64 bit microsecond system timer is used to emulate the RTC timer.

The RTT is retained during light and deep sleep as well as during a restart. The RTC hardware timer is used for this purpose, regardless of whether an external 32.768 kHz crystal is connected to the ESP32x SoC or the internal 150 kHz RC oscillator is used. All current timer values are saved in the RTC memory before entering a sleep mode or restart and are restored after when waking up or restarting.

Note
The RTT implementation is also used to implement a RTC (Real Time Clock) peripheral. For this purpose the module rt_rtc is automatically enabled when the feature periph_rtc is used.

Back to table of contents

UART Interfaces

ESP32x SoCs integrate up to three UART devices, depending on the specific ESP32x SoC variant (family).

The pin configuration of the UART device UART_DEV(n) is defined in the board-specific peripheral configuration by

where n can be in range of 0 and UART_NUMOF_MAX-1. If they are not defined, the according UART interface UART_DEV(n) is not used, for example:

#define UART1_TX GPIO10 // TxD signal of UART_DEV(1)
#define UART1_RX GPIO9 // RxD signal of UART_DEV(1)

The pin configuration of UART interfaces can be changed by application specific configurations by overriding the according UARTn_* symbols.

The default configuration of the UART interfaces for ESP32x SoC boards depend on used ESP32x SoC family, for details see:

Note
To ensure that the UARTn_* symbols define the configuration for UART_DEV(n), the configuration of the UART interfaces UART_DEV(n) must be in continuous ascending order of n. That is, if UART_DEV(1) is to be used by defining the UART1_* symbols, UART_DEV(0) must also be used by defining the UART0_* symbols, and if UART_DEV(2) is to be used by defining the UART2_* symbols, UART_DEV(0) and UART_DEV(1) must also be used by defining the UART0_* and UART1_* symbols

UART_NUMOF is determined automatically from the board-specific peripheral configuration for UART_DEV(n).

UART_DEV(0) has usually a fixed pin configuration that is used by all ESP32x boards as standard configuration for the console. The GPIOs used for UART_DEV(0) depend on the ESP32x SoC family.

Back to table of contents

CAN Interfaces

ESP32x SoCs intregate a Two-Wire Automotive Interface (TWAI) controller which is compatible with the NXP SJA1000 CAN controller. Thus, it is CAN 2.0B specification compliant and supports two message formats:

Note
  • The TWAI controller does not support CAN-FD and is not CAN-FD tolerant.
  • The TWAI controller does not support SJA1000's sleep mode and wake-up functionality.

As with the SJA1000, the TWAI controller provides only the data link layer and the physical layer signaling sublayer. Therefore, depending on physical layer requirements, an external CAN transceiver is required which converts the CAN-RX and CAN-TX signals of the TWAI controller into CAN_H and CAN_L bus signals, e.g., the MCP2551 or SN65HVD23X transceiver for compatibility with ISO 11898-2.

If module periph_can is used, the low-level CAN driver for the TWAI controller is enabled. It provides a CAN DLL device that can be used with RIOT's CAN protocol stack. It uses the TWAI CANcontroller in SJA1000 PeliCAN mode. Please refer the SJA1000 Datasheet for detailed information about the TWAI controller and its programming.

The pin configuration of the CAN transceiver interface is usually defined in board specific peripheral configuration by

Example:

#define CAN_TX GPIO10 // CAN TX transceiver signal
#define CAN_RX GPIO9 // CAN RX transceiver signal

If the pin configuration is not defined, the following default configuration is used which can be overridden by the application, see section Application-Specific Configurations.

Device Signal Pin Symbol Remarks
CAN TX GPIO5 CAN_TX optional, can be overridden
CAN RX GPIO35 CAN_RX optional, can be overridden

If the board has an external transceiver module connected to the ESP32x SoC on-board, module periph_can should be provided as feature in board's Makefile.features

FEATURES_PROVIDED += periph_can # CAN peripheral interface

Otherwise, the application has to add the periph_can module in its makefile when needed.

Back to table of contents

Power Management

Power Modes

The RIOT port for ESP32x SoCs implements RIOT's layered power management. It supports the following operating modes:

Since the peripherals are not working during Light-sleep and Deep-sleep, the CPU cannot be woken up by internal interrupt sources such as timers. Therefore, RIOT's layered power management can't select them as idle power mode. They are therefore blocked for normal operation. The application has to select them explicitly using the #pm_set function. RIOT's layered power management can only select either Modem-sleep or Active as the lowest unblocked mode.

But also in Modem-sleep or Active mode, the lowest possible power level is used. For this purpose, the Xtensa ISA instruction waiti is used, which saves power by setting the current interrupt level, turning off the processor logic and waiting for an interrupt.

Back to table of contents

Using Power Modes

Modem-sleep mode and Active mode are the default operating modes dependent on whether the WiFi interface is used. They are selected automatically by the system.

To enter the Light-sleep or the Deep-sleep mode, function #pm_set has to be used with the according mode ESP_PM_LIGHT_SLEEP or ESP_PM_DEEP_SLEEP as parameter. To exit from these modes, several wake-up sources can be used.

Back to table of contents

Wake-up Sources in <em>Light-sleep</em>

Possible wake-up sources for the Light-sleep mode are:

Note
Since the digital core (MCU) is stalled during Light-sleep, it is not possible to use timers like periph_timer or ztimer as wake-up source.
Warning
Since only level interrupts are supported in Light-sleep mode, defined edge interrupts of type #GPIO_RISING and #GPIO_FALLING are implicitly mapped to GPIO_HIGH and GPIO_LOW, respectively, when entering Light-sleep mode.

Back to table of contents

Wake-up Sources in <em>Deep-sleep</em> Mode

Possible Wake-up sources for the Deep-sleep mode are:

Note
RTC GPIOs are the GPIOs that are realized by the RTC unit and can also be used as ADC channels. See section GPIO pins and ADC Channels for more information.

Back to table of contents

Configuration

Several definitions can be used during compile time to configure the Light-sleep and the Deep-sleep mode:

Parameter Default Mode Description
ESP_PM_GPIO_HOLD not defined Deep Hold GPIO output level if defined
ESP_PM_WUP_PINS none Deep GPIOs used as wake-up source
ESP_PM_WUP_LEVEL ESP_PM_WUP_PINS_ANY_HIGH Deep Level for wake-up pins to wake-up
ESP_PM_WUP_UART0 disabled Light Positive UART0 RxD signal edges to wake-up
ESP_PM_WUP_UART1 disabled Light Positive UART1 RxD signal edges to wake-up


Note
  • If ESP_PM_GPIO_HOLD is defined, GPIOs hold their last output level when entering Deep-sleep mode. Please note that only RTC GPIOs can hold their output value in Deep-sleep mode. When restarting after a deep sleep, the GPIOs are reset to their default configuration, which is usually the input-only mode. This means that the output level of the GPIOs in output mode may change for up to 150 ms until the GPIOs are reconfigured by the application in output mode. If a continuous output level for such GPIOs is important, external pullups/pulldowns should be used for these GPIOs to pull them to a specific level during deep sleep and restart instead of defining ESP_PM_GPIO_HOLD.
  • ESP_PM_WUP_PINS specifies either a single RTC GPIO or a comma separated list of RTC GPIOs that are used as wake-up source in Deep-sleep mode.
  • ESP_PM_WUP_LEVEL specifies the level for the wake-up pins in Deep-sleep mode:
    • ESP_PM_WUP_PINS_ANY_HIGH (default) - The system is woken up when any of the GPIOs specified in ESP_PM_WUP_PINS becomes HIGH.
    • ESP_PM_WUP_PINS_ANY_LOW - The system is woken up when any of the GPIOs specified in ESP_PM_WUP_PINS becomes LOW (only available with the ESP32-C3 variant).
    • ESP_PM_WUP_PINS_ALL_LOW - The system is woken up when all GPIOs specified in ESP_PM_WUP_PINS become LOW (not available with the ESP32-C3 variant).
  • ESP_PM_WUP_UART0 and ESP_PM_WUP_UART1 define the number of positive edges of the RxD signal of the respective UART that are necessary to wake up the system in the Light-sleep mode. The value must be greater than 2, otherwise UART is not activated as wake-up source. The specified value is reduced by 2 so that ESP_PM_WUP_UART0 or ESP_PM_WUP_UART1 plus 2 is the number of positive edges required to wake up.

In the following example the system shall be woken up from Deep-sleep if the pulled-up pin GPIO25 (ESP_PM_WUP_PINS=GPIO25) goes LOW (ESP_PM_WUP_LEVEL=ESP_PM_WUP_PINS_ALL_LOW). The last GPIO output values are held (ESP_PM_GPIO_HOLD) in Deep-sleep mode. From Light-sleep the system can be woken up by any of the GPIOs defined as input with enabled interrupt or if the RxD signal of UART0 goes HIGH at least 4 times (ESP_PM_WUP_UART0=6).

CFLAGS='-DESP_PM_WUP_PINS=GPIO25 -DESP_PM_WUP_LEVEL=ESP_PM_WUP_PINS_ALL_LOW \
-DESP_PM_WUP_UART0=6 -DESP_PM_GPIO_HOLD' \
make BOARD=esp32-wroom-32 -C tests/periph_pm

Back to table of contents

Saving Data in <em>Deep-sleep</em> Mode

In Deep-sleep mode the SRAM is powered down. However, the slow RTC memory can be retained. Therefore, data that must be retained during Deep-sleep and the subsequent system restart, must be stored in the slow RTC memory. For that purpose, use

For example:

static int _i_value __attribute__((section(".rtc.bss"))); // set to 0 at power on
static int _u_value __attribute__((section(".rtc.data"))) = 1; // initialized

Back to table of contents

Other Peripherals

The RIOT port for ESP32x SoCs also supports:

Back to table of contents

Special On-board Peripherals

SPI RAM Modules

Dependent on the ESP32x SoC variant (family), external SPI RAM can be connected to the SPI interface that is driven by the SPI1 controller (SPI1_HOST). For example, all boards that use the ESP32-WROVER modules have already integrated such SPI RAM. The connected SPI RAM is treated as PSRAM (pseudo-static RAM) and is integrated into the heap.

However, the external SPI RAM requires 4 data lines and thus can only be used in qout (quad output) or qio (quad input/output) flash mode, which makes GPIO9 and GPIO10 unavailable for other purposes. Therefore, if needed, the SPI RAM must be explicitly enabled in the makefile of the application.

USEMODULE += esp_spi_ram
Note
  • When the SPI RAM is enabled using the esp_spi_ram, the ESP32x SoC uses four data lines to access the external SPI RAM in qout (quad output) flash mode. Therefore, GPIO9 and GPIO10 are used as SPI data lines and are not available for other purposes.
  • Enabling SPI RAM for modules that don't have SPI RAM may lead to boot problems for some modules. For others it simply throws an error message.

Newer ESP32x SoC variants (families) like the ESP32-S3 support the Octal SPI mode for Flash and SPI RAMs. Depending on the chip or module used, it must be specified in the board definition whether the optional SPI RAM is used in Octal SPI mode (feature esp_spi_oct). In this case additional GPIOs are needed as data lines and are not available for other purposes. If the feature esp_spi_oct is defined for a board, the pseudomodule esp_spi_oct is automatically enabled when the SPI RAM is used.

Back to table of contents

SPIFFS Device

The RIOT port for ESP32x SoCs implements a MTD system drive mtd0 using the on-board SPI flash memory. This MTD system drive can be used together with SPIFFS and VFS to realize a persistent file system.

To use the MTD system drive with SPIFFS, the esp_spiffs module has to be enabled in the makefile of the application:

USEMODULE += esp_spiffs

When SPIFFS is enabled, the MTD system drive is formatted with SPIFFS the first time the system is started. The start address of the MTD system drive in the SPI flash memory is defined by the board configuration:

#define SPI_FLASH_DRIVE_START 0x200000

If this start address is set to 0, as in the default board configuration, the first possible multiple of 0x100000 (1 MiB) will be used in the free SPI flash memory determined from the partition table.

Please refer file $RIOTBASE/tests/unittests/test-spiffs/tests-spiffs.c for more information on how to use SPIFFS and VFS together with a MTD device mtd0 alias MTD_0.

Back to table of contents

Network Interfaces

ESP32x SoCs integrate different network interfaces:

Note
EMAC interface is only available in ESP32 SoCs.

Back to table of contents

Ethernet MAC Network Interface

ESP32 SoC variant (family) provides an Ethernet MAC layer module (EMAC) according to the IEEE 802.3 standard which can be used together with an external physical layer chip (PHY) to realize a 100/10 Mbps Ethernet interface. The following PHY layer chips are supported:

The RIOT port for ESP32 SoCs realizes a netdev driver for the EMAC (module esp_eth) which uses RIOT's standard Ethernet interface.

If the board has one of the supported PHY layer chips connected to the ESP32, feature esp_eth should be enabled.

FEATURES_PROVIDED += periph_eth

Furthermore, module esp_eth should be by default in board's Makefile.dep when module netdev_default is used.

ifneq (,$(filter netdev_default,$(USEMODULE)))
USEMODULE += esp_eth
endif

Otherwise, the application has to add the esp_eth module in its makefile when needed.

Note
The board has to have one of the supported PHY chips to be able to use the Ethernet MAC module.

Back to table of contents

WiFi Network Interface

The RIOT port for ESP32x SoC implements a netdev driver for the built-in WiFi interface. This netdev driver supports WPA2 personal mode as well as WPA2 enterprise mode.

Back to table of contents

WPA2 personal mode

To use the WiFi netdev driver in WPA2 personal mode with a preshared key (PSK), module esp_wifi has to be enabled.

USEMODULE += esp_wifi

Furthermore, the following configuration parameters have to be defined:

Parameter Default Description
ESP_WIFI_SSID "RIOT_AP" SSID of the AP to be used.
ESP_WIFI_PASS - Passphrase used for the AP as clear text (max. 64 chars).
ESP_WIFI_STACKSIZE THREAD_STACKSIZE_DEFAULT Stack size used for the WiFi netdev driver thread.


These configuration parameter definitions, as well as enabling the esp_wifi module, can be done either in the makefile of the project or at make command line, for example:

USEMODULE=esp_wifi \
CFLAGS='-DESP_WIFI_SSID=\"MySSID\" -DESP_WIFI_PASS=\"MyPassphrase\"' \
make -C examples/gnrc_networking BOARD=...
Note
  • Module esp_wifi is not enabled automatically when module netdev_default is used.
  • Leave 'ESP_WIFI_PASS' undefined to connect to an open WiFi access point.
  • The Wifi network interface (module esp_wifi) and the ESP-NOW network interface (module esp_now) can be used simultaneously, for example, to realize a border router for a mesh network which uses ESP-NOW.

Back to table of contents

WPA2 Enterprise Mode

To use the WiFi netdev driver in WPA2 enterprise mode with IEEE 802.1X/EAP authentication, module esp_wifi_enterprise has to be enabled.

USEMODULE += esp_wifi_enterprise

It supports the following EAP authentication methods:

As inner (phase 2) EAP authentication method, only MSCHAPv2 is supported.

To use module esp_wifi_enterprise with these authentication methods, the following configuration parameters have to be defined:

Parameter Default Description
ESP_WIFI_SSID "RIOT_AP" SSID of the AP to be used.
ESP_WIFI_EAP_ID none Optional anonymous identity used in phase 1 (outer) EAP authentication.[1]
ESP_WIFI_EAP_USER none User name used in phase 2 (inner) EAP authentication.
ESP_WIFI_EAP_PASS none Password used in phase 2 (inner) EAP authentication.
ESP_WIFI_STACKSIZE THREAD_STACKSIZE_DEFAULT Stack size used for the WiFi netdev driver thread.


[1] If the optional anonymous identy ESP_WIFI_EAP_ID is not defined, the user name ESP_WIFI_EAP_USER defined for phase 2 (inner) EAP authentication is used as identity in phase 1.

These configuration parameter definitions, as well as enabling the esp_wifi module, can be done either in the makefile of the project or at make command line, for example:

USEMODULE=esp_wifi_enterprise \
CFLAGS='-DESP_WIFI_SSID=\"MySSID\" -DESP_WIFI_EAP_ID=\"anonymous\" -DESP_WIFI_EAP_USER=\"MyUserName\" -DESP_WIFI_EAP_PASS=\"MyPassphrase\"' \
make -C examples/gnrc_networking BOARD=...
Note
  • Since there is no possibility to add the CA certificate to the RIOT image, the verification of the AP certificate is not yet supported.
  • Module esp_wifi_enterprise is not enabled automatically when module netdev_default is used.
  • The Wifi network interface (module esp_wifi_enterprise) and the ESP-NOW network interface (module esp_now) can be used simultaneously, for example, to realize a border router for a mesh network which uses ESP-NOW. In this case the ESP-NOW interface must use the same channel as the AP of the infrastructure WiFi network. All ESP-NOW nodes must therefore be compiled with the channel of the AP as value for the parameter 'ESP_NOW_CHANNEL'.

Back to table of contents

WiFi SoftAP Network Interface

The RIOT port for the ESP32x SoCs supports a netdev interface for the ESP WiFi SoftAP mode. Module esp_wifi_ap has to be enabled to use it.

The following parameters can be configured:

Parameter Default Description
ESP_WIFI_SSID "RIOT_AP" Static SSID definition for the SoftAP
ESP_WIFI_PASS none The password for the WiFi SoftAP network interface.[1]
ESP_WIFI_SSID_DYNAMIC 0 Defines whether dynamic SSID is used for the SoftAP [2].
ESP_WIFI_SSID_HIDDEN 0 Defines whether the SoftAP SSID should be hidden.
ESP_WIFI_MAX_CONN 4 The maximum number of connections for the SoftAP.
ESP_WIFI_BEACON_INTERVAL 100 The beacon interval time in milliseconds for the SoftAP.
ESP_WIFI_STACKSIZE THREAD_STACKSIZE_DEFAULT Stack size used for the WiFi netdev driver thread.


[1] If no password is provided, the interface will be "open", otherwise it uses WPA2-PSK authentication mode.
[2] If #ESP_WIFI_SSID_DYNAMIC is set to 1, a dynamic SSID is generated for the SoftAP by extending the defined SSID (ESP_WIFI_SSID) with the MAC address of the SoftAP interface used, e.g.: RIOT_AP_aabbccddeeff

These configuration parameter definitions, as well as enabling the esp_wifi_ap module, can be done either in the makefile of the project or at make command line, for example:

USEMODULE=esp_wifi_ap \
CFLAGS='-DESP_WIFI_SSID=\"MySSID\" -DESP_WIFI_PASS=\"MyPassphrase\" -DESP_WIFI_MAX_CONN=1' \
make -C examples/gnrc_networking BOARD=...
Note
  • The esp_wifi_ap module is not used by default when netdev_default is used.
  • Supports open and WPA2-PSK authentication modes.
  • The ESP-NOW network interface and the WiFi SoftAP network interface can not be used simultaneously.
Warning
The SoftAP may or may not be at all reliable sometimes, this is a known problem with the Wi-Fi network interface, even on the official ESP-IDF. The problem is that the AP doesn't cache multicast data for connected stations, and if stations connected to the AP are power save enabled, they may experience multicast packet loss. This affects RIOT, because NDP relies on multicast packets to work correctly. Refer to the SDK documentation from Espressif on AP Sleep for more information.

Back to table of contents

ESP-NOW Network Interface

With ESP-NOW, ESP32x SoCs provide a connectionless communication technology, featuring short packet transmission. It applies the IEEE802.11 Action Vendor frame technology, along with the IE function developed by Espressif, and CCMP encryption technology, realizing a secure, connectionless communication solution.

The RIOT port for ESP32x SoCs implements in module esp_now a netdev driver which uses ESP-NOW to provide a link layer interface to a meshed network of ESP32x nodes. In this network, each node can send short packets with up to 250 data bytes to all other nodes that are visible in its range.

Note
Module esp_nowmodule is not enabled automatically if the netdev_default module is used. Instead, the application has to add the esp_now module in its makefile when needed.
USEMODULE += esp_now

For ESP-NOW, ESP32x nodes are used in WiFi SoftAP + Station mode to advertise their SSID and become visible to other ESP32x nodes. The SSID of an ESP32x node is the concatenation of the prefix RIOT_ESP_ with the MAC address of its SoftAP WiFi interface. The driver periodically scans all visible ESP32x nodes.

The following parameters are defined for ESP-NOW nodes. These parameters can be overridden by application-specific board configurations.

Parameter Default Description
ESP_NOW_SCAN_PERIOD_MS 10000UL Defines the period in ms at which an node scans for other nodes in its range. The default period is 10 s.
ESP_NOW_SOFT_AP_PASS "ThisistheRIOTporttoESP" Defines the passphrase as clear text (max. 64 chars) that is used for the SoftAP interface of ESP-NOW nodes. It has to be same for all nodes in one network.
ESP_NOW_CHANNEL 6 Defines the channel that is used as the broadcast medium by all nodes together.
ESP_NOW_KEY NULL Defines a key that is used for encrypted communication between nodes. If it is NULL, encryption is disabled. The key has to be of type uint8_t[16] and has to be exactly 16 bytes long.


Note
The ESP-NOW network interface (module esp_now) and the Wifi network interface (module esp_wifi or esp_wifi_enterprise) can be used simultaneously, for example, to realize a border router for a mesh network which uses ESP-NOW. In this case the ESP-NOW interface must use the same channel as the AP of the infrastructure WiFi network. All ESP-NOW nodes must therefore be compiled with the channel of the AP asvalue for the parameter 'ESP_NOW_CHANNEL'.

Back to table of contents

Bluetooth Network Interface

The following ESP32x SoC variants (families) integrate a Bluetooth Link Controller and a Bluetooth baseband system:

The Bluetooth interface can be used with the Bluetooth host implementation of the NimBLE package. Use one of the nimble_* modules for different applications to enable the Bluetooth interface and the NimBLE host implementation. Please refer to the NimBle package documentation for details.

Back to table of contents

Other Network Devices

RIOT provides a number of driver modules for different types of network devices, e.g., IEEE 802.15.4 radio modules and Ethernet modules. The RIOT port for ESP32x SoCs has been tested with the following network devices:

Back to table of contents

Using MRF24J40 (module mrf24j40)

To use MRF24J40 based IEEE 802.15.4 modules as network device, the mrf24j40 driver module has to be added to the makefile of the application:

USEMODULE += mrf24j40

The driver parameters that have to be defined by the board configuration for the MRF24J40 driver module are:

Parameter Description
MRF24J40_PARAM_CS GPIO used as CS signal
MRF24J40_PARAM_INT GPIO used as interrupt signal
MRF24J40_PARAM_RESET GPIO used as reset signal

Since each board has different GPIO configurations, refer to the board documentation for the GPIOs recommended for the MRF24J40.

Note
The reset signal of the MRF24J40 based network device can be connected with the ESP32x RESET/EN pin which is broken out on most boards. This keeps the GPIO free defined by MRF24J40_PARAM_RESET free for other purposes.

Back to table of contents

Using ENC28J60 (module enc28j60)

To use ENC28J60 Ethernet modules as network device, the enc28j60 driver module has to be added to the makefile of the application:

USEMODULE += enc28j60

The parameters that have to be defined by board configuration for the ENC28J60 driver module are:

Parameter Description
ENC28J60_PARAM_CS GPIO used as CS signal
ENC28J60_PARAM_INT GPIO used as interrupt signal
ENC28J60_PARAM_RESET GPIO used as reset signal

Since each board has different GPIO configurations, refer to the board documentation for the GPIOs recommended for the ENC28J60.

Note
The reset signal of the ENC28J60 based network device can be connected with the ESP32x RESET/EN pin which is broken out on most boards. This keeps the GPIO free defined by #ENC28J60_PARAM_RESET free for other purposes.

Back to table of contents

Application-Specific Configurations

The board-specific configuration files board.h and periph_conf.h as well well as the driver parameter configuration files <driver>_params.h define the default configurations for peripherals and device driver modules. These are, for example, the GPIOs used, bus interfaces used or available bus speeds. Because there are many possible configurations and many different application requirements, these default configurations are usually only a compromise between different requirements.

Therefore, it is often necessary to change some of these default configurations for individual applications. For example, while many PWM channels are needed in one application, another application does not need PWM channels, but many ADC channels.

There are two ways to give the application the ability to change some of these default configurations:

Back to table of contents

Make Variable CFLAGS

Using the CFLAGS make variable at the command line, board or driver parameter definitions can be overridden.

Example:

CFLAGS='-DESP_LCD_PLUGGED_IN=1 -DLIS3DH_PARAM_INT2=GPIO4'

When a larger number of board definitions needs be overridden, this approach becomes impractical. In that case, an application-specific board configuration file located in application directory can be used, see sections below.

Back to table of contents

Application-Specific Board Configuration

To override default board configurations, simply create an application-specific board configuration file $APPDIR/board.h in the source directory $APPDIR of the application and add the definitions to be overridden. To force the preprocessor to include board's original board.h after that, add the include_next preprocessor directive as the last line.

For example to override the default definition of the GPIOs that are used as PWM channels, the application-specific board configuration file $APPDIR/board.h could look like the following:

#ifdef CPU_ESP32
#define PWM0_CHANNEL_GPIOS { GPIO12, GPIO13, GPIO14, GPIO15 }
#endif
#include_next "board.h"

It is important that the application-specific board configuration $APPDIR/board.h is included first. Insert the following line as the first line to the application makefile $APPDIR/Makefile.

INCLUDES += -I$(APPDIR)
Note
To make such application-specific board configurations dependent on a certain ESP32x SoC variant (family) or a particular ESP32x board, you should always enclose these definitions in the following constructs
#ifdef CPU_FAM_ESP32 // specific ESP32x SoC variant (family)
...
#endif
#ifdef BOARD_ESP32_WROVER_KIT // specific ESP32x board
...
#endif

Back to table of contents

Application-Specific Driver Configuration

Using the approach for overriding board configurations, the parameters of drivers that are typically defined in drivers/<device>/include/<device>_params.h can be overridden. For that purpose just create an application-specific driver parameter file $APPDIR/<device>_params.h in the source directory $APPDIR of the application and add the definitions to be overridden. To force the preprocessor to include driver's original <device>_params.h after that, add the include_next preprocessor directive as the last line.

For example, to override a GPIO used for LIS3DH sensor, the application-specific driver parameter file $APPDIR/<device>_params.h could look like the following:

#ifdef CPU_FAM_ESP32
#define LIS3DH_PARAM_INT2 (GPIO_PIN(0, 4))
#endif
#include_next "lis3dh_params.h"

It is important to ensure that the application-specific driver parameter file $APPDIR/<device>_params.h is included first. Insert the following line as the first line to the application makefile $APPDIR/Makefile.

INCLUDES += -I$(APPDIR)
Note
To make such application-specific board configurations dependent on a certain ESP32x SoC variant (family) or a particular ESP32x board, you should always enclose these definitions in the following constructs
#ifdef CPU_FAM_ESP32 // specific ESP32x SoC variant (family)
...
#endif
#ifdef BOARD_ESP32_WROVER_KIT // specific ESP32x board
...
#endif

Back to table of contents

Debugging

JTAG Debugging

ESP32x SoCs integrate a JTAG interface for On-Chip Debugging. The GPIOs connected to this JTAG interface depend on the ESP32x SoC variant (family). For details, see:

This JTAG interface can be used with OpenOCD and GDB for On-Chip debugging of your software on instruction level. When you compile your software with debugging information (module esp_gdb) you can debug on source code level as well.

Note
When debugging, the GPIOs used for the JTAG interface must not be used for anything else.

Some ESP32 boards like the ESP-WROVER-KIT V3 or the ESP32-Ethernet-Kit have a USB bridge with JTAG interface on-board that can be directly used for JTAG debugging.

Other ESP32x SoC variants (families) have an built in USB-to-JTAG bridge that can be used without additional chips. For details, see:

To use the JTAG debugging, the precompiled version of OpenOCD for ESP32 has to be installed using the toolchain install script while being in RIOT's root directory, see also section Using Local Toolchain Installation.

$ dist/tools/esptools/install.sh openocd

Before OpenOCD can be used, the PATH variable has to be set correctly and the OPENOCD variable has to be exported using the following command.

$ . dist/tools/esptools/export.sh openocd

Once the PATH variable as well as the OPENOCD variable are set, the debugging session can be started using either

$ PROGRAMMER=openocd USEMODULE=esp_jtag \
make debug BOARD=esp32-wrover-kit

if the board defines an OpenOCD board configuration file or using

$ PROGRAMMER=openocd USEMODULE=esp_jtag OPENOCD_CONFIG=board/esp-wroom-32.cfg \
make debug BOARD=esp32-wroom-32

if the board does not define an OpenOCD board configuration file.

Note
The board will be reset, but not flashed with this command. However, flashing would be also possible with OpenOCD and the JTAG interface using command:
$ PROGRAMMER=openocd USEMODULE=esp_jtag \
make flash BOARD=esp32-wrover-kit

Detailed information on how to configure the JTAG interface of the respective ESP32x SoC variant (family) can be found in ESP-IDF Programming Guide:

Back to table of contents

QEMU Mode and GDB

RIOT applications that do not require interaction with real hardware such as GPIOs, I2C or SPI devices, WiFi interface, etc. can also be debugged using QEMU for ESP32. For this purpose, either QEMU for ESP32 must be installed, see section Local Toolchain Installation or the RIOT Docker build image has to be used in which QEMU for ESP32 is already installed.

To use QEMU for ESP32, an application has to be built with esp_qemu module enabled, for example with local toolchain installation

$ USEMODULE=esp_qemu make flash BOARD=esp32-wroom-32 -C tests/shell

or with RIOT Docker build image

$ BUILD_IN_DOCKER=1 DOCKER="sudo docker" \
USEMODULE=esp_qemu make flash BOARD=esp32-wroom-32 -C tests/shell

Instead of flashing the image to the target hardware, a binary image named qemu_flash_image.bin is created in the target directory. In addition, two ROM files rom.bin and rom1.bin are copied to the target directory. These files can then be used with QEMU for ESP32 to debug the application in GDB without having the hardware. The binary image qemu_flash_image.bin represents a 4 MByte Flash image.

QEMU for ESP32 can then be started with command:

$ qemu-system-xtensa \
-s -machine esp32 \
-drive file=tests/shell/bin/esp32-wroom-32/qemu_flash_image.bin,if=mtd,format=raw \
-serial tcp::5555,server,nowait

To interact with the application on the emulated ESP32 in QEMU, a second terminal is required in which the telnet command is used to communicate with the application on localhost using TCP port 5555:

$ telnet localhost 5555
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
main(): This is RIOT! (Version: 2022.04)
test_shell.
> help
help
Command Description
---------------------------------------
bufsize Get the shell's buffer size
start_test starts a test
...

To debug the application in QEMU for ESP32, another terminal is required:

$ xtensa-esp32-elf-gdb tests/shell/bin/esp32-wroom-32/tests_shell.elf
GNU gdb (crosstool-NG crosstool-ng-1.22.0-80-g6c4433a5) 7.10
Copyright (C) 2015 Free Software Foundation, Inc.
...
Reading symbols from tests/shell/bin/esp32-wroom-32/tests_shell.elf...done.
(gdb) target remote :1234
Remote debugging using :1234
pm_set (mode=2) at cpu/esp32/periph/pm.c:117
117 return;
(gdb)
void pm_set(unsigned mode)
Switches the MCU to a new power mode.

QEMU for ESP32 can also be used in RIOT Docker build image. For that purpose QEMU has to be started in the Docker container.

$ sudo docker run --rm -i -t -u $UID -v $(pwd):/data/riotbuild riot/riotbuild
riotbuild@container-id:~$ USEMODULE=esp_qemu make flash BOARD=esp32-wroom-32 -C tests/shell
riotbuild@container-id:~$ qemu-system-xtensa \
-s -machine esp32 \
-drive file=tests/shell/bin/esp32-wroom-32/qemu_flash_image.bin,if=mtd,format=raw \
-serial tcp::5555,server,nowait

In a second and a third terminal, you need to execute a shell in the same RIOT Docker container where QEMU for ESP32 was started. The required container ID <container-id> is shown in the prompt of the terminal in which QEMU for ESP32 was started.

$ sudo docker docker exec -it <container-id> bash
riotbuild@container-id:~$telnet localhost 5555
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
main(): This is RIOT! (Version: 2022.04)
test_shell.
>
$ sudo docker docker exec -it <container-id> bash
riotbuild@container-id:~$ xtensa-esp32-elf-gdb tests/shell/bin/esp32-wroom-32/tests_shell.elf
GNU gdb (crosstool-NG crosstool-ng-1.22.0-80-g6c4433a5) 7.10
Copyright (C) 2015 Free Software Foundation, Inc.
...
Reading symbols from tests/shell/bin/esp32-wroom-32/tests_shell.elf...done.
(gdb) target remote :1234
Remote debugging using :1234
pm_set (mode=2) at cpu/esp32/periph/pm.c:117
117 return;
(gdb)

Back to table of contents

Modules

 ESP-IDF Interface API
 ESP-IDF Interface API.
 
 ESP-NOW netdev interface
 WiFi based ESP-NOW network device driver.
 
 ESP-WiFi netdev interface
 Network device driver for the ESP SoC WiFi interface.
 
 ESP32 Bluetooth LE HCI for NimBLE host
 ESP32 Bluetooth LE HCI implementation for NimBLE host.
 
 ESP32 CAN controller
 CAN controller driver for ESP32 (esp_can)
 
 ESP32 Ethernet netdev interface
 ESP32 ethernet network device driver.
 
 ESP32 compile configurations
 Compile-time configuration macros for ESP32x SoCs.
 
 ESP32 family
 Specific properties of ESP32 variant (family)
 
 ESP32-C3 family
 Specific properties of ESP32-C3 variant (family)
 
 ESP32-S2 family
 Specific properties of ESP32-S2 variant (family)
 
 ESP32-S3 family
 Specific properties of ESP32-S3 variant (family)
 

Files

file  sdkconfig_default_common.h
 Default SDK configuration for all ESP32x SoC bootloaders.
 
file  sdkconfig_default_esp32.h
 Default SDK configuration for the ESP32 SoC bootloader.
 
file  sdkconfig_default_esp32c3.h
 Default SDK configuration for the ESP32-C3 SoC bootloader.
 
file  sdkconfig_default_esp32s2.h
 Default SDK configuration for the ESP32-S2 SoC bootloader.
 
file  sdkconfig_default_esp32s3.h
 Default SDK configuration for the ESP32-S3 SoC bootloader.
 
file  esp_log.h
 Wrapper for source code compatibility of ESP-IDF log with RIOT's log module.
 
file  adc_arch.h
 Architecture specific ADC definitions and functions for ESP32.
 
file  adc_arch_private.h
 Architecture specific internal ADC functions for ESP32.
 
file  cpu_conf_esp32.h
 Compile-time configuration macros for ESP32 SoCs.
 
file  cpu_conf_esp32c3.h
 Compile-time configuration macros for ESP32-C3 SoCs.
 
file  cpu_conf_esp32s2.h
 Compile-time configuration macros for ESP32-S2 SoCs.
 
file  cpu_conf_esp32s3.h
 Compile-time configuration macros for ESP32-S3 SoCs.
 
file  FreeRTOSConfig.h
 FreeRTOS configuration for ESP32 as required by ESP-IDF.
 
file  gpio_arch.h
 Architecture specific GPIO functions for ESP32.
 
file  gpio_ll_arch.h
 CPU specific part of the Peripheral GPIO Low-Level API.
 
file  irq_arch.h
 Implementation of the kernels irq interface.
 
file  newlib.h
 Wrapper for sys/features.h.
 
file  periph_cpu.h
 Peripheral configuration that is common for all ESP32x SoCs.
 
file  periph_cpu_esp32.h
 ESP32 specific peripheral configuration.
 
file  periph_cpu_esp32c3.h
 ESP32-C3 specific peripheral configuration.
 
file  periph_cpu_esp32s2.h
 ESP32-S2 specific peripheral configuration.
 
file  periph_cpu_esp32s3.h
 ESP32-S3 specific peripheral configuration.
 
file  rtt_arch.h
 Architecture specific RTT functions for ESP32.
 
file  sdkconfig.h
 SDK configuration used by ESP-IDF for all ESP32x SoC variants (families)
 
file  sdkconfig_esp32.h
 SDK configuration used by the ESP-IDF for ESP32 SoC variant (family)
 
file  sdkconfig_esp32c3.h
 SDK configuration used by the ESP-IDF for ESP32-C3 SoC variant (family)
 
file  sdkconfig_esp32s2.h
 SDK configuration used by the ESP-IDF for ESP32-S2 SoC variant (family)
 
file  sdkconfig_esp32s3.h
 SDK configuration used by the ESP-IDF for ESP32-S3 SoC variant (family)
 
file  features.h
 Wrapper for sys/features.h.
 
file  lock.h
 Wrapper for sys/lock.h.
 
file  syscalls.h
 Implementation of required system calls.