Microphone_PDM_nRF52 Class Reference

#include <Microphone_PDM_nRF52.h>

Inheritance diagram for Microphone_PDM_nRF52:

Static Public Attributes
static const size_t	BUFFER_SIZE_SAMPLES = 512
static const size_t	NUM_BUFFERS = 2

Protected Member Functions
	Microphone_PDM_nRF52 ()
virtual	~Microphone_PDM_nRF52 ()
virtual int	init ()
virtual int	uninit ()
virtual int	start ()
virtual int	stop ()
virtual bool	samplesAvailable () const
virtual bool	copySamples (void *pSamples)
virtual bool	noCopySamples (std::function< void(void *pSamples, size_t numSamples)>callback)
size_t	getNumberOfSamples () const
size_t	copySrcIncrement () const
Protected Member Functions inherited from Microphone_PDM_Base
	Microphone_PDM_Base (size_t numSamples)
virtual	~Microphone_PDM_Base ()
void	copySamplesInternal (const int16_t *src, uint8_t *dst) const
virtual size_t	copySrcIncrement () const

Additional Inherited Members
Public Types inherited from Microphone_PDM_Base
enum class	OutputSize { UNSIGNED_8 , SIGNED_16 , RAW_SIGNED_16 }
enum class	Range {   RANGE_128 = 0 , RANGE_256 , RANGE_512 , RANGE_1024 ,   RANGE_2048 , RANGE_4096 , RANGE_8192 , RANGE_16384 ,   RANGE_32768 }
Public Member Functions inherited from Microphone_PDM_Base
int	getSampleRate () const
Protected Attributes inherited from Microphone_PDM_Base
pin_t	clkPin = A0
pin_t	datPin = A1
bool	stereoMode = false
int	sampleRate
OutputSize	outputSize = OutputSize::SIGNED_16
Range	range = Range::RANGE_2048
size_t	numSamples

Detailed Description

MCU-specific implementation of PDM for the nRF52.

This class is used on the Boron, B Series SoM, Tracker, and Argon.

You do not instantiate this class directly; it's automatically created when you use the Microphone_PDM singleton.

Member Function Documentation

copySamples()

virtual bool Microphone_PDM_nRF52::copySamples ( void *  pSamples )

protectedvirtual

Copy samples from the DMA buffer to your buffer.

Parameters

pSamples

Pointer to buffer to copy samples to. It must be at least getNumberOfSamples() samples in length.

Returns

true There were samples available and they were copied.

false There were no samples available. Your buffer is unmodified.

The size of the buffer in bytes will depend on the outputSize. If UNSIGNED_8, then it's getNumberOfSamples() bytes. If SIGNED_16 or RAW_SIGNED_16, then it's 2 * getNumberOfSamples().

You can skip calling samplesAvailable() and just call copySamples which will return false in the same cases where samplesAvailable() would have returned false.

Reimplemented in Microphone_PDM.

copySrcIncrement()

size_t Microphone_PDM_nRF52::copySrcIncrement ( ) const

protectedvirtual

How much to increment src in copySamplesInternal. Used internally.

Returns

size_t number of bytes

This is almost always 1. The exception is if you are using 8000 Hz sampling on the nRF52. In this case, every other sample is skipped and the subclass overrides this to return 2.

Override of virtual method in base class Microphone_PDM_Base

Reimplemented from Microphone_PDM_Base.

getNumberOfSamples()

size_t Microphone_PDM_nRF52::getNumberOfSamples ( ) const

inlineprotected

Return the number of int16_t samples that copySamples will copy.

Returns

size_t Number of uint16_t samples. Number of bytes is twice that value

You will never get a partial buffer of data. The number of samples is a constant that is determined by the MCU type at compile time and does not change.

On the nRF52, it's 512 samples (1024 bytes), except in one case: If you set a sample rate of 8000 Hz, it will be 256 samples because the hardware only samples at 16000 Hz but the code will automatically discard every other sample so there will only be 256 samples.

init()

virtual int Microphone_PDM_nRF52::init ( )

protectedvirtual

Initialize the PDM module.

This is often done from setup(). You can defer it until you're ready to sample if desired, calling right before start().

Reimplemented in Microphone_PDM.

noCopySamples()

virtual bool Microphone_PDM_nRF52::noCopySamples ( std::function< void(void *pSamples, size_t numSamples)>  callback )

protectedvirtual

Alternative API to get samples.

Parameters

callback

Callback function or lambda

Returns

true

false

Alternative API that does not require a buffer to be passed in. You should only use this if you can consume the buffer immediately without blocking.

The callback function or lamba has this prototype:

void callback(void *pSamples, size_t numSamples)

It will be called with a pointer to the samples (in the DMA buffer) and the number of samples (not bytes!) of data. The number of bytes will vary depending on the outputSize.

You can skip calling samplesAvailable() and just call noCopySamples which will return false in the same cases where samplesAvailable() would have returned false.

Reimplemented in Microphone_PDM.

samplesAvailable()

virtual bool Microphone_PDM_nRF52::samplesAvailable ( ) const

protectedvirtual

Return true if there is data available to be copied using copySamples.

Returns

true

false

Reimplemented in Microphone_PDM.

start()

virtual int Microphone_PDM_nRF52::start ( )

protectedvirtual

Start sampling.

Reimplemented in Microphone_PDM.

stop()

virtual int Microphone_PDM_nRF52::stop ( )

protectedvirtual

Stop sampling.

Reimplemented in Microphone_PDM.

uninit()

virtual int Microphone_PDM_nRF52::uninit ( )

protectedvirtual

Uninitialize the PDM module.

You normally will just initialize it once and only start and stop it as necessary, however you can completely uninitialize it if desired. The clkPin will be reset to INPUT mode.

Reimplemented in Microphone_PDM.

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The documentation for this class was generated from the following file:

• src/Microphone_PDM_nRF52.h