DAC Direct Digital Synthesis

Detailed Description

Files
file	dac_dds.h
	Use a DAC to play a buffer of samples.

Data Structures
struct	dac_dds_params_t
	Configuration struct for a DAC DDS channel. More...

Macros
#define	DAC_FLAG_8BIT   (0x0)
	A sample has a resolution of 8 bit.
#define	DAC_FLAG_16BIT   (0x1)
	A sample has a resolution of 16 bit.

Typedefs
typedef void(*	dac_dds_cb_t) (void *arg)
	The callback that will be called when the end of the current sample buffer has been reached.
typedef uint8_t	dac_dds_t
	Index of the DAC DDS channel.

Functions
void	dac_dds_init (dac_dds_t dac, uint16_t sample_rate, uint8_t flags, dac_dds_cb_t cb, void *cb_arg)
	Initialize a DAC for playing audio samples A user defined callback can be provided that will be called when the next buffer can be queued.
void	dac_dds_set_cb (dac_dds_t dac, dac_dds_cb_t cb, void *cb_arg)
	Change the 'buffer done' callback.
bool	dac_dds_play (dac_dds_t dac, const void *buf, size_t len)
	Play a buffer of (audio) samples on a DAC.
void	dac_dds_stop (dac_dds_t dac)
	Stop playback of the current sample buffer.

Macro Definition Documentation

DAC_FLAG_16BIT

#define DAC_FLAG_16BIT   (0x1)

A sample has a resolution of 16 bit.

Definition at line 90 of file dac_dds.h.

DAC_FLAG_8BIT

#define DAC_FLAG_8BIT   (0x0)

A sample has a resolution of 8 bit.

Definition at line 83 of file dac_dds.h.

Typedef Documentation

dac_dds_cb_t

typedef void(* dac_dds_cb_t) (void *arg)

The callback that will be called when the end of the current sample buffer has been reached.

Should be used to start filling the next sample buffer with dac_dds_play.

Note

Will be called in interrupt context. Only use the callback to signal a thread. Don't directly fill the sample buffer in the callback.

Definition at line 61 of file dac_dds.h.

dac_dds_t

typedef uint8_t dac_dds_t

Index of the DAC DDS channel.

Definition at line 77 of file dac_dds.h.

Function Documentation

dac_dds_init()

void dac_dds_init	(	dac_dds_t	dac,
		uint16_t	sample_rate,
		uint8_t	flags,
		dac_dds_cb_t	cb,
		void *	cb_arg
	)

Initialize a DAC for playing audio samples A user defined callback can be provided that will be called when the next buffer can be queued.

Warning

This feature is experimental!

Parameters

[in]	dac	The DAC to initialize
[in]	sample_rate	The sample rate in Hz
[in]	flags	Optional flags (DAC_FLAG_16BIT)
[in]	cb	Will be called when the next buffer can be queued
[in]	cb_arg	Callback argument

dac_dds_play()

bool dac_dds_play	(	dac_dds_t	dac,
		const void *	buf,
		size_t	len
	)

Play a buffer of (audio) samples on a DAC.

     If this function is called while another buffer is already
     being played, the new `buf` will be played when the current
     buffer has finished playing.

     The DAC implementations allows one buffer to be queued
     (double buffering).

     Whenever a new buffer can be queued, the @ref dac_dds_cb_t
     callback function will be executed.

Warning

This feature is experimental!

Parameters

[in]	dac	The DAC to play the sample on
[in]	buf	A buffer with (audio) samples
[in]	len	Number of bytes to be played

Returns

true if the buffer was queued while another buffer is currently playing. false if the new buffer is played immediately. That means playing was just started or an underrun occurred.

dac_dds_set_cb()

void dac_dds_set_cb	(	dac_dds_t	dac,
		dac_dds_cb_t	cb,
		void *	cb_arg
	)

Change the 'buffer done' callback.

A user defined callback can be provided that will be called when the next buffer can be queued. This function can be used to change the callback on the fly.

Passing in a cb of NULL can be used to only update the arg without updating the cb. Conversely, to clear the callback, both cb and cb_arg need to be passed in as NULL.

Warning

This feature is experimental!

Parameters

[in]	dac	The DAC to configure
[in]	cb	Called when the played buffer is done
[in]	cb_arg	Callback argument

dac_dds_stop()

void dac_dds_stop

(

dac_dds_t

dac

)

Stop playback of the current sample buffer.

Parameters

[in]

dac

The DAC to stop