PDM rx service which uses a streaming channel to send a block of data by pointer. More...

#include <PdmRx.hpp>

Inheritance diagram for mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >:

Public Member Functions
uint32_t	ReadPort ()
	Read a word of PDM data from the port. More...

void	SendBlock (uint32_t block[CHANNELS_IN *SUBBLOCKS])
	Send a block of PDM data to a listener. More...

void	Init (port_t p_pdm_mics)
	Initialize this object with a channel and port. More...

void	MapChannels (unsigned map[CHANNELS_OUT])
	Set the input-output mapping for all output channels. More...

void	MapChannel (unsigned out_channel, unsigned in_channel)
	Set the input-output mapping for a single output channel. More...

void	InstallISR ()
	Install ISR for PDM reception on the current core. More...

void	UnmaskISR ()
	Unmask interrupts on the current core.

uint32_t *	GetPdmBlock ()
	Get a block of PDM data. More...

Public Member Functions inherited from mic_array::PdmRxService< CHANNELS_IN *SUBBLOCKS, StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS > >
void	SetPort (port_t p_pdm_mics)
	Set the port from which to collect PDM samples.

void	ProcessNext ()
	Perform a port read and if a new block has completed, signal.

void	ThreadEntry ()
	Entry point for PDM processing thread. More...

Additional Inherited Members
Static Public Attributes inherited from mic_array::PdmRxService< CHANNELS_IN *SUBBLOCKS, StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS > >
static constexpr unsigned	BlockSize
	Number of words of PDM data per block.

Protected Attributes inherited from mic_array::PdmRxService< CHANNELS_IN *SUBBLOCKS, StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS > >
port_t	p_pdm_mics
	Port from which to collect PDM data.

unsigned	phase
	Number of words left to capture for the current block.

uint32_t	block_data [2][BLOCK_SIZE]
	Buffers for PDM data blocks.

uint32_t *	blocks [2]
	PDM block redirection pointers. More...

Detailed Description

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>
class mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >

PDM rx service which uses a streaming channel to send a block of data by pointer.

This class can run the PDM rx service either as a stand-alone thread or through an interrupt.

Inter-context Transfer

A streaming channel is used to transfer control of the PDM data block between contexts (i.e. thread->thread or ISR->thread).

The MicArray unit receives blocks of PDM data from an instance of this class by calling GetPdmBlock(), which blocks until a new PDM block is available.

Layouts

The buffer transferred by SendBlock() contains CHANNELS_IN*SUBBLOCKS words of PDM data forCHANNELS_INmicrophone channels. The words are stored in reverse order of arrival. Seedeinterleave_pdm_samples<>()` for additional details on this format.

Within GetPdmBlock() (i.e. mic array thread) the PDM data block is deinterleaved and copied to another buffer in the format required by the decimator component, which is returned by GetPdmBlock(). This buffer contains samples for CHANNELS_OUT microphone channels.

Channel Filtering

In some cases an application may be required to capture more microphone channels than should actually be processed by subsequent processing stages (including the decimator component). For example, this may be the case if 4 microphone channels are desired but only an 8 bit wide port is physically available to capture the samples.

This class template has a parameter both for the number of channels to be captured by the port (CHANNELS_IN), as well as for the number of channels that are to be output for consumption by the MicArray's decimator component (CHANNELS_OUT).

When the PDM microphones are in an SDR configuration, CHANNELS_IN must be the width (in bits) of the xCore port to which the microphones are physically connected. When in a DDR configuration, CHANNELS_IN must be twice the width (in bits) of the xCore port to which the microphones are physically connected.

CHANNELS_OUT is the number of microphone channels to be consumed by the decimator unit (i.e. must be the same as the MIC_COUNT template parameter of the decimator component). If all port pins are connected to microphones, this parameter will generally be the same as CHANNELS_IN.

Channel Index (Re-)Mapping

The input channel index of a microphone depends on the pin to which it is connected. Each pin connected to a port has a bit index for that port, given in the 'Signal Description and GPIO' section of your package's datasheet.

Suppose an N-bit port is used to capture microphone data, and a microphone is connected to bit B of that port. In an SDR microphone configuration, the input channel index of that microphone is B – the same as the port bit index.

In a DDR configuration, that microphone will be on either input channel index B or B+N, depending on whether that microphone is configured for in-phase capture or out-of-phase capture.

Sometimes it may be desirable to re-order the microphone channel indices. This is likely the case, for example, when CHANNELS_IN > CHANNELS_OUT.

By default output channels are mapped from the input channels with the same index. If CHANNELS_IN > CHANNELS_OUT, this means that the input channels with the highest CHANNELS_IN-CHANNELS_OUT indices are dropped by default.

The MapChannel() and MapChannels() methods can be used to specify a non-default mapping from input channel indices to output channel indices. It takes a pointer to a CHANNELS_OUT-element array specifying the input channel index for each output channel.

Template Parameters

CHANNELS_IN	The number of microphone channels to be captured by the port.
CHANNELS_OUT	The number of microphone channels to be delivered by this `StandardPdmRxService` instance.
SUBBLOCKS	The number of 32-sample sub-blocks to be captured for each microphone channel.

Member Function Documentation

◆ GetPdmBlock()

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>

uint32_t * mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >::GetPdmBlock

Get a block of PDM data.

Because blocks of PDM samples are delivered by pointer, the caller must either copy the samples or finish processing them before the next block of samples is ready, or the data will be clobbered.

Note: This is a blocking call.

Returns: Pointer to block of PDM data.

◆ Init()

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>

void mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >::Init ( port_t p_pdm_mics )

Initialize this object with a channel and port.

Parameters

p_pdm_mics Port to receive PDM data on.

◆ InstallISR()

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>

void mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >::InstallISR

Install ISR for PDM reception on the current core.

Note: This does not unmask interrupts.

◆ MapChannel()

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>

void mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >::MapChannel	(	unsigned	out_channel,
		unsigned	in_channel
	)

Set the input-output mapping for a single output channel.

By default, input channel index k maps to output channel index k.

This method overrides that behavior for a single output channel, configuring output channel out_channel to be derived from input channel in_channel.

Note: Changing the channel mapping while the mic array unit is running is not recommended.

Parameters

out_channel	Output channel index to be re-mapped.
in_channel	New source channel index for `out_channel`.

◆ MapChannels()

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>

void mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >::MapChannels ( unsigned map[CHANNELS_OUT] )

Set the input-output mapping for all output channels.

By default, input channel index k maps to output channel index k.

This method overrides that behavior for all channels, re-mapping each output channel such that output channel k is derived from input channel map[k].

Note: Changing the channel mapping while the mic array unit is running is not recommended.

Parameters

map	Array containing new channel map.

◆ ReadPort()

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>

uint32_t mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >::ReadPort

Read a word of PDM data from the port.

Returns: A uint32_t containing 32 PDM samples. If MIC_COUNT >= 2 the samples from each port will be interleaved together.

◆ SendBlock()

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>

void mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >::SendBlock ( uint32_t block[CHANNELS_IN *SUBBLOCKS] )

Send a block of PDM data to a listener.

Parameters

block PDM data to send.

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

/build/modules/io/modules/mic_array/lib_mic_array/api/mic_array/cpp/PdmRx.hpp

Public Member Functions

Additional Inherited Members

Detailed Description

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS> class mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >

Member Function Documentation

◆ GetPdmBlock()

◆ Init()

◆ InstallISR()

◆ MapChannel()

◆ MapChannels()

◆ ReadPort()

◆ SendBlock()

template<unsigned CHANNELS_IN, unsigned CHANNELS_OUT, unsigned SUBBLOCKS>
class mic_array::StandardPdmRxService< CHANNELS_IN, CHANNELS_OUT, SUBBLOCKS >