Support for using the ATmega1284P as standalone board. More...

Detailed Description

Support for using the ATmega1284P as standalone board.

Overview

As the ATmega1284P can run from the internal oscillator, placing it on a breadboard, connecting an USB-UART adapter and power is enough to run RIOT on it. (An ISP programmer will be needed to program it; or to program a bootloader to subsequently allow programming via UART.)

MCU

MCU	ATmega1284p
Family	AVR/ATmega
Vendor	Microchip (previously Atmel)
RAM	16KiB
Flash	128KiB
EEPROM	4KiB
Frequency	8MHz (up to 20MHz with external clock)
Timers	3 (2x 8bit, 1x 16bit)
ADCs	6 analog input pins
UARTs	1
SPIs	1
I2Cs	1 (called TWI)
Vcc	2.7V - 5.5V (when clocked at 8MHz)
Datasheet	Official datasheet

Pinout

Pinout of the ATmega1284P

The pinout image was posted in the Arduino Forum. All credit goes to its poster, hansibull.

Clock Frequency

The ATmega1284P has two internal oscillators clocked at 8MHz and at 128kHz that allow it to be operated without any external clock source or crystal. By default the fuses are configured to use the internal 8MHz oscillator, but the CKDIV8 fuse is set, so that the clock is divided down to 1MHz. By disabling the CKDIV8 fuse the clock will operate at 8MHz. This is highly encouraged, and can be done with:

avrdude -c atmelice -p m1284p -B 32 -U lfuse:w:0xc2:m

(Replace atmelice with the programmer you are using. The -B 32 might be needed for some programmers to successfully communicate with ATmegas clocked at less than 2MHz. It will no longer be needed after disabling CKDIV8.)

By setting the environment variable ATMEGA1284P_CLOCK to a custom frequency in Hz (e.g. 1000000 for 1MHz), this core clock can be changed easily. Refer to the datasheet on how to configure the ATmega1284p to use an external crystal, an external clock source or the clock divider.

Relation Between Supply Voltage, Clock Frequency and Power Consumption

A higher supply voltage results in a higher current drawn. Thus, lower power consumption can be achieved by using a lower supply voltage. However, higher clock frequencies require higher supply voltages for reliable operation.

The lowest possible supply voltage at 8 MHz is 2.7V (with some safety margin).

Flashing the Device

In order to flash the ATmega1284P without a bootloader, an ISP programmer is needed. Connect the programmer as follows:

ISCP pin	ATmega1284P
MISO	7/PB6/MISO
VCC	10/VCC
SCK	8/PB7/SCK
MOSI	6/PB5/MOSI
RESET	9/RESET
Ground	11/GND

The tool avrdude needs to be installed. When using the Atmel ICE for connected via JTAG for programming, running

make BOARD=atmega1284p flash

will take care of everything. To use the programmer <FOOBAR> instead, run

make BOARD=atmega1284p PROGRAMMER=<FOOBAR> flash

Serial Terminal

Connect a TTL adapter with pins 14/RXD0 and 15/TXD0 an run

make BOARD=atmega1284p term

Please note that the supply voltage should be compatible with the logic level of the TTL adapter. Usually everything between 3.3 V and 5 V should work.

On-Chip Debugging

In order to debug the ATmega1284P, an compatible debugger is needed. The Atmel ICE is the ~~cheapest~~ least expensive option currently available. (But at least it can program and debug pretty much all Atmel AVR and ARM chips.)

Once the Atmel ICE is correctly connected, the ATmega1284P has the JTAG interface enabled, and the required software is installed, debugging can be started using

make debug

Note: If you are using a different debugger than the Atmel ICE, you have to export the AVR_DEBUGDEVICE environment variable to the required flag to pass to AVaRICE, e.g. when using the AVR Dragon you have to export AVR_DEBUGDEVICE=--dragon. If the debug device is not connected via USB, you also need to export AVR_DEBUGINTERFACE to the correct value.

Software Requirements

In order to debug you'll need an GDB version with AVR support and AVaRICE. Note that AVaRICE sadly is not being actively maintained and the latest release will not compile on most systems. Thus, unless your distribution already ships a package of the SVN version of AVaRICE, you'll have to build the tool from source.

JTAG Pin Mapping

Pin Name	Pin	Signal	Atmel ICE Pin
PC5	27	TDI	JTAG-9
PC4	26	TDO	JTAG-3
PC3	25	TMS	JTAG-5
PC2	24	TCK	JTAG-1
VCC	10	VTG	JTAG-4
GND	11	GND	JTAG-2

Fuse Settings

The JTAGEN fuse has to be set in order to use the JTAG interface. The JTAG pins will no longer be available as GPIOs when this fuse is set. With the default settings the MCUs are preprogrammed during manufacturing, the JTAGEN fuse is already set. So with a new and unused package, you're ready directly ready to go.

Files
file	board.h
	Board specific definitions for the standalone ATmega1284P "board".

file	periph_conf.h
	Peripheral MCU configuration for the ATmega1284p standalone "board".