Detailed Description

PDM driver implementation for a CC26XX PDM controller.

============================================================================

The PDM header file should be included in an application as follows:

#include <ti/drivers/pdm/PDMCC26XX.h>

Overview

This driver is written to be able to perform continuous audio streaming of PDM data from a microphone. It also controls one DIO to be able to turn on power to the microphone.

This PDM driver performs two operations that requires processing

PDM to PCM conversion
PCM compression (optional)

When producing 16kHz output, the driver is configured to process 256 bytes of PDM data provided by the I2S hardware module at a time, sampled at 1.024 Mbps. The PDM driver consequently receives such a buffer approximately every 2ms. A frame of PDMCC26XX_Params.retBufSizeInBytes PCM data bytes minus four metadata bytes is provided to the application after being filled by all or part of one or more 64 byte buffers of PCM data derived from the 256 bytes of PDM data. The resulting PCM frame provided to the application is a 16bit PCM signal sampled at 16kHz.

When providing 8kHz PCM output, the driver processes 512 bytes of PDM data at a time. At a sample rate of 1.024 Mbps, this yields a PDM buffer to process ever 4ms. These 512 bytes of PDM data are filtered and decimated to yield 64 bytes of PCM output.

The driver creates a separate task to run in.

Note: The application must allow for the PDM driver task to run often enough to process the data received from I2S driver approximately every 2ms in 16kHz PCM output mode or 4ms in 8kHz PCM output mode. The amount of processing is approximately equal but the latency requirements differ.

The driver currently only samples on a single edge of the I2S clock.

General Behaviour

Before using PDM on CC26XX:

The PDM driver is initialized by calling PDMCC26XX_init(). This should be done in main before BIOS_start() is called.
The PDM system dependencies are set by calling PDMCC26XX_open(). The driver is also marked as taken. Prior to this the system should call PDMCC26XX_init(). The driver also automatically allocates the first PDMCC26XX_pcmBuffer of the size specified by the application in PDMCC26XX_Params.retBufSizeInBytes. This call also reserves the pins for the microphone signal and power specified in the board file.
Do not start steaming data until the device is running off of the high frequency external oscilator (XOSC_HF). The XOSC_HF is required to generate a jitter-free I2S audio clock. When switching to XOSC_HF, several SCLK_HF clock cycles and thus audio clock cycles are missed. Both jitter and missing audio clock cycles causes severe degredation in audio noise performance! After booting, the device runs off of the high frequency RC oscillator (RCOSC_HF) by default. Set a dependency on the XOSC_HF to turn it on and switch to it when it is ready. Register a power notification for the XOSC_HF having switched. Wait until after this notification occurs to call PDMCC26XX_startStream(). When waking up from standby, the XOSC_HF will automatically be turned on and switched to if the dependency was set before going into standby. Again, only call PDMCC26XX_startStream() after the application was notified of the switch to XOSC_HF. PDMCC26XX_open() may be called before running off of XOSC_HF.

While using PDM on CC26XX:

When PDMCC26XX_open() is called, the driver allocates one PCM buffer on the heap and the I2S module tries to allocate enough memory for its PDM buffers.
When PDMCC26XX_startStream() is called, the I2S driver starts processing the pdm stream, the PDM driver resets the internal state of the decimation filter, sets the driver to drop the first MAX(PDM_DECIMATION_STARTUP_DELAY_IN_SAMPLES, PDMCC26XX_Params.startupDelayWithClockInSamples), and resets the metaData (including the sequence number). The driver will keep allocating PDMCC26XX_pcmBuffers on the heap and keep them in a queue until they are requested by the application. From now on, callbacks are generated every time a buffer is ready; if callbacks are asked for.
Data is acquired by the application by calling PDMCC26XX_requestBuffer(). After processing the buffer, the application is responsible for freeing the memory allocated for the buffer in a timely manner.
The stream is stopped when PDMCC26XX_stopStream() is called. Note that this is a blocking call that will wait until the I2S hardware has gracefully shut down. This will take at most 4ms, unless an error occurs. Any PCM buffers remaining must be released by the application as usual. The system is allowed to enter standby again after PDMCC26XX_stopStream() is called.
The memory held by the I2S module is freed upon calling PDMCC26XX_close(). Any completed PCM buffers must be processed and freed by the application.

After PDM operation has ended:

Release system dependencies and free up all memory on the heap allocated for the PDM driver by calling PDMCC26XX_close().

Error Handling

The application is notified of errors via the registered callback function.

Heap Full

If the application fails to consume PCM buffers fast enough and the heap is full when driver tries to allocate a new buffer, the driver will drop all new incoming data until a buffer can be allocated to store it. Data is dropped one PCM data buffer at a time , even though it is streamed into the device and copied into the buffer in smaller chunks. This is done to keep the data expected in any buffer in sync with the sequence number of the buffer that keeps incrementing even when the buffer is dopped. The application may keep track of lost frames by comparing sequence numbers.

Hence, the PDM stream will never have a buffer overflow, but if the memory available in the heap is too low it may lose frames because because there is nowhere to put the incoming

If the heap frees up again and the PDM task runs, it will automatically resume normal operation again. The only application-observable difference is the incremented version number.

PDM Task Not Serviced In Time

The application must permit the PDM task to run often enough that it can process a PDM buffer every 2ms on average. If the application requires a larger contiguous segment of processing time, the I2S hwi may run out of empty buffers to fill with new PDM data. When the I2S driver runs out of empty PDM buffers it will pop a buffer from the full buffer queue and overwrite its old data. The I2S driver notifies the PDM driver that it has dropped a PDM buffer. Once it runs again, the PDM driver will drop enough additional PCM samples such that the sequence numbers of the PCM buffers remain aligned with the data in the audio stream. The latency between when the PDM task was last serviced and when it must be serviced again to avoid losing data is specified by PDMCC26XX_Params::pdmBufferQueueDepth. This permitted latency increases by 2ms or 4ms for each increment of pdmBufferQueueDepth.

PDMCC26XX_open Failing

PDMCC26XX_open() returns NULL and rolls back all prior parts of the initialisation if any part of the initialisation fails. The following can cause PDMCC26XX_open() to fail:

The driver is already open
The heap is full when the application calls PDMCC26XX_open()
The PIN driver could not allocate the requested pins for the PDM driver
The I2S driver failed to initialise

PDMCC26XX_startStream Failing

PDMCC26XX_startStream() returns false if it fails. The following can cause PDMCC26XX_startStream() to fail:

The driver is already streaming
The I2S driver could not successfully start reading the pdm stream
The I2S driver could not allocate enough memory for the specified number of PDM buffers

PDMCC26XX_stopStream Failing

PDMCC26XX_stopStream() returns false if it fails. The following can cause PDMCC26XX_stopStream() to fail:

The driver is not currently streaming

Power Management

The PDMCC26XX driver sets a power constraint while streaming to keep the device out of standby. When the stream has ended, the power constraint is released.

The following statements are valid:

After PDMCC26XX_open(): the device is still allowed to enter standby.
During PDMCC26XX_startStream(): the device cannot enter standby.
After PDMCC26XX_stopStream() succeeds: the device can enter standby.
If PDMCC26XX_close() is called: the device can enter standby.

Standard Use Case

The standard use case involves calling PDMCC26XX_open() once and calling PDMCC26XX_startStream() and PDMCC26XX_stopStream() to start and stop the stream as needed. PDMCC26XX_close() is called when the PDM driver will no longer be needed again. In order for the PDM driver task to run, the application pends on a semaphore that is posted in the PDMCC26XX_Params::callbackFxn. In this example, the application requests 128 buffers. In a real application, the process of pending on a semaphore, requesting a buffer, and freeing it would be repeated as often as required by the use case before stopping the stream.

void bufRdy_callback(PDMCC26XX_Handle handle, PDMCC26XX_StreamNotification *streamNotification)
{
    if (streamNotification->status == PDMCC26XX_STREAM_BLOCK_READY || streamNotification->status == PDMCC26XX_STREAM_BLOCK_READY_BUT_PDM_OVERFLOW){
        SemaphoreP_post(SemaphoreP_handle(&bufferReadySemaphore));
    }
    else {
        // Handle the error
    }
}
static void applicationTask(UArg a0, UArg a1){
    SemaphoreP_Params semParams;
    PDMCC26XX_BufferRequest bufferRequest;
    PDMCC26XX_Params pdmParams;
    const uint16_t returnBufferSize = 64;
    const uint8_t numberOfPcmBuffersToRequest = 128;
    // Initialize semaphore
    SemaphoreP_Params_init(&semParams);
    semParams.mode = SemaphoreP_Mode_BINARY;
    SemaphoreP_construct(&bufferReadySemaphore, 0, &semParams);
    // Set up parameters for PDM streaming with compression
    PDMCC26XX_Params_init(&pdmParams);
    pdmParams.callbackFxn = bufRdy_callback;
    pdmParams.micPowerActiveHigh = true;
    pdmParams.applyCompression = true;
    pdmParams.retBufSizeInBytes = returnBufferSize;
    pdmParams.mallocFxn = &malloc;
    pdmParams.freeFxn = &free;
    // Try to open the PDM driver
    if(pdmHandle = PDMCC26XX_open(&pdmParams) == NULL){
        // Handle PDMCC26XX_open() failing
    }
    // Try to start streaming
    if(PDMCC26XX_startStream(pdmHandle)){
        uint8_t pcmBuffersRequestedSoFar;
        // Request numberOfPcmBuffersToRequest buffers and then stop the stream
        for (pcmBuffersRequestedSoFar = 0; pcmBuffersRequestedSoFar < numberOfPcmBuffersToRequest; pcmBuffersRequestedSoFar++){
            // Pend on the semaphore until a buffer is available from the PDM driver
            SemaphoreP_pend(SemaphoreP_handle(&bufferReadySemaphore), BIOS_WAIT_FOREVER);
            // Now request a buffer as it was indicated that one is available
            PDMCC26XX_requestBuffer(pdmHandle, &bufferRequest);
            // Process bufferRequest
            // Free the buffer
            my_free(bufferRequest.buffer, returnBufferSize);
        }
        // Try to stop the stream
        if(!PDMCC26XX_stopStream(pdmHandle)){
            // Handle PDMCC26XX_stopStream() failing
        }
    }
    else{
        // Handle PDMCC26XX_startStream() failing
    }
}

8kHz PCM output

By default, the PCM output of the driver has a sampling frequency of fs = 16kHz. There is an alternate signal processing chain that returns PCM output with fs = 8kHz. This example shows how to alter the standard use-case to set this up.

void bufRdy_callback(PDMCC26XX_Handle handle, PDMCC26XX_StreamNotification *streamNotification)
{
    if (streamNotification->status == PDMCC26XX_STREAM_BLOCK_READY || streamNotification->status == PDMCC26XX_STREAM_BLOCK_READY_BUT_PDM_OVERFLOW){
        SemaphoreP_post(SemaphoreP_handle(&bufferReadySemaphore));
    }
    else {
        // Handle the error
    }
}
static void applicationTask(UArg a0, UArg a1){
    SemaphoreP_Params semParams;
    PDMCC26XX_BufferRequest bufferRequest;
    PDMCC26XX_Params pdmParams;
    const uint16_t returnBufferSize = 64;
    const uint8_t numberOfPcmBuffersToRequest = 128;
    // Initialize semaphore
    SemaphoreP_Params_init(&semParams);
    semParams.mode = SemaphoreP_Mode_BINARY;
    SemaphoreP_construct(&bufferReadySemaphore, 0, &semParams);
    // Set up parameters for PDM streaming with compression
    PDMCC26XX_Params_init(&pdmParams);
    pdmParams.callbackFxn = bufRdy_callback;
    pdmParams.micPowerActiveHigh = true;
    pdmParams.applyCompression = true;
    pdmParams.retBufSizeInBytes = returnBufferSize;
    pdmParams.mallocFxn = &malloc;
    pdmParams.freeFxn = &free;
    // Configure the params to use 8kHz PCM output
    pdmParams.pcmSampleRate = PDMCC26XX_PCM_SAMPLE_RATE_8K
    // Try to open the PDM driver
    if(pdmHandle = PDMCC26XX_open(&pdmParams) == NULL){
        // Handle PDMCC26XX_open() failing
    }
    // Try to start streaming
    if(PDMCC26XX_startStream(pdmHandle)){
        uint8_t pcmBuffersRequestedSoFar;
        // Request numberOfPcmBuffersToRequest buffers and then stop the stream
        for (pcmBuffersRequestedSoFar = 0; pcmBuffersRequestedSoFar < numberOfPcmBuffersToRequest; pcmBuffersRequestedSoFar++){
            // Pend on the semaphore until a buffer is available from the PDM driver
            SemaphoreP_pend(SemaphoreP_handle(&bufferReadySemaphore), BIOS_WAIT_FOREVER);
            // Now request a buffer as it was indicated that one is available
            PDMCC26XX_requestBuffer(pdmHandle, &bufferRequest);
            // Process bufferRequest
            // Free the buffer
            my_free(bufferRequest.buffer, returnBufferSize);
        }
        // Try to stop the stream
        if(!PDMCC26XX_stopStream(pdmHandle)){
            // Handle PDMCC26XX_stopStream() failing
        }
    }
    else{
        // Handle PDMCC26XX_startStream() failing
    }
}

#include <ti/drivers/dpl/HwiP.h>
#include <ti/drivers/dpl/SemaphoreP.h>
#include <ti/drivers/PIN.h>
#include <ti/drivers/Power.h>
#include <ti/drivers/power/PowerCC26XX.h>

Include dependency graph for PDMCC26XX.h:

Go to the source code of this file.

Data Structures
struct	PDMCC26XX_metaData
	Metadata associated with an array of PCM data. More...

struct	PDMCC26XX_pcmBuffer
	PCM buffer pointed to in a PDMCC26XX_BufferRequest. More...

struct	PDMCC26XX_Config
	The PDMCC26XX_Config structure contains a set of pointers used to characterize the PDMCC26XX driver implementation. More...

struct	PDMCC26XX_HWAttrs
	PDMCC26XX Hardware attributes. More...

struct	PDMCC26XX_StreamNotification
	A PDMCC26XX_StreamNotification data structure is used with PDMCC26XX_CallbackFxn(). Provides notification about available buffers and potential errors. More...

struct	PDMCC26XX_BufferRequest
	A PDMCC26XX_BufferRequest data structure is used with PDMCC26XX_requestBuffer(). More...

struct	PDMCC26XX_Params
	PDMCC26XX Parameters are used to with the PDMCC26XX_open() call. Default values for these parameters are set using PDMCC26XX_Params_init(). More...

struct	PDMCC26XX_Object
	PDMCC26XX Object. More...

Macros
#define	PDM_TASK_STACK_SIZE 850

#define	PCM_SAMPLE_SIZE 16

#define	PCM_COMPRESSION_RATE 4

#define	MINIMUM_PDM_BUFFER_QUEUE_DEPTH 3

#define	PCM_METADATA_SIZE sizeof(PDMCC26XX_metaData)

Typedefs
typedef void (	PDMCC26XX_MallocFxn) (size_t memSize)
	PDMCC26XX_MallocFxn is a function pointer for the malloc function to be used by the driver. More...

typedef void(*	PDMCC26XX_FreeFxn) (void *ptr, size_t memSize)
	PDMCC26XX_FreeFxn is a function pointer for the free function to be used by the driver. This is needed for memory clean up, if something goes wrong. More...

typedef bool(*	PDMCC26XX_Pdm2PcmFxn) (const void pdmInBuffer, uint32_t decimationState, const int32_t biquadCoefficients, int16_t pcmOutBuffer)
	Function that converts PDM input buffer to PCM output. More...

typedef PDMCC26XX_Config *	PDMCC26XX_Handle
	A handle that is returned from a PDMCC26XX_open() call. More...

typedef void(*	PDMCC26XX_CallbackFxn) (PDMCC26XX_Handle handle, PDMCC26XX_StreamNotification *streamNotification)
	The definition of a callback function used when buffers are ready. More...

Enumerations
enum	PDMCC26XX_Status { PDMCC26XX_STREAM_IDLE, PDMCC26XX_STREAM_BLOCK_READY, PDMCC26XX_STREAM_BLOCK_READY_BUT_PDM_OVERFLOW, PDMCC26XX_STREAM_ERROR, PDMCC26XX_STREAM_STOPPING, PDMCC26XX_STREAM_STOPPED, PDMCC26XX_STREAM_FAILED_TO_STOP }
	Status codes that are set by the PDM driver. More...

enum	PDMCC26XX_PcmSampleRate { PDMCC26XX_PCM_SAMPLE_RATE_16K = 0, PDMCC26XX_PCM_SAMPLE_RATE_8K }
	PCM output sample rates supported by the driver. More...

enum	PDMCC26XX_Gain { PDMCC26XX_GAIN_24 = 1318, PDMCC26XX_GAIN_18 = 660, PDMCC26XX_GAIN_12 = 331, PDMCC26XX_GAIN_6 = 166, PDMCC26XX_GAIN_0 = 83, PDMCC26XX_GAIN_END }
	Predefined gain settings. More...

Functions
void	PDMCC26XX_init (PDMCC26XX_Handle handle)
	PDM CC26XX initialization. More...

PDMCC26XX_Handle	PDMCC26XX_open (PDMCC26XX_Params *params)
	Function to initialize the CC26XX PDM peripheral specified by the particular handle. The parameter specifies which mode the PDM will operate. More...

void	PDMCC26XX_close (PDMCC26XX_Handle handle)
	Function to close a given CC26XX PDM peripheral specified by the PDM handle. More...

bool	PDMCC26XX_startStream (PDMCC26XX_Handle handle)
	Function to start streaming PDM data. More...

bool	PDMCC26XX_stopStream (PDMCC26XX_Handle handle)
	Function to stop streaming PDM data. More...

bool	PDMCC26XX_requestBuffer (PDMCC26XX_Handle handle, PDMCC26XX_BufferRequest *bufferRequest)
	Function for requesting buffer. More...

void	PDMCC26XX_Params_init (PDMCC26XX_Params *params)

Variables
const PDMCC26XX_Config	PDMCC26XX_config []

Macro Definition Documentation

§ PDM_TASK_STACK_SIZE

#define PDM_TASK_STACK_SIZE 850

Defines TI-RTOS stack size allocation. It is a conservative estimate. Change this to save a few bytes of RAM on stack allocation. The stack usage is independent of the PCM return buffer size specified by the application. When using logging, increase this value. This value is also dependent on the malloc and free function implementations provided by the application as both are called from PDM task context.

§ PCM_SAMPLE_SIZE

#define PCM_SAMPLE_SIZE 16

Uncompressed PCM sample size in bits

Note: Internal use only since only 16 bits are supported

§ PCM_COMPRESSION_RATE

#define PCM_COMPRESSION_RATE 4

Compression rate if compression is enabled

§ MINIMUM_PDM_BUFFER_QUEUE_DEPTH

#define MINIMUM_PDM_BUFFER_QUEUE_DEPTH 3

Minimum number of PDM buffers required by the driver to safely use the I2S module

§ PCM_METADATA_SIZE

#define PCM_METADATA_SIZE sizeof(PDMCC26XX_metaData)

PCM data metadata size. When a buffer is requested there will be metadata prepended. In other words the pointer returned points to the metadata header. Depending on the mode, this contains different information. The first byte is always an 8-bit sequence number.

Typedef Documentation

§ PDMCC26XX_MallocFxn

typedef void*(* PDMCC26XX_MallocFxn) (size_t memSize)

PDMCC26XX_MallocFxn is a function pointer for the malloc function to be used by the driver.

§ PDMCC26XX_FreeFxn

typedef void(* PDMCC26XX_FreeFxn) (void *ptr, size_t memSize)

PDMCC26XX_FreeFxn is a function pointer for the free function to be used by the driver. This is needed for memory clean up, if something goes wrong.

§ PDMCC26XX_Pdm2PcmFxn

typedef bool(* PDMCC26XX_Pdm2PcmFxn) (const void *pdmInBuffer, uint32_t *decimationState, const int32_t *biquadCoefficients, int16_t *pcmOutBuffer)

Function that converts PDM input buffer to PCM output.

Parameters

pdmInBuffer	Input PDM buffer
decimationState	CIC decimator state
biquadCoefficients	Coefficient table for the n-stage biquad IIR filter
pcmOutBuffer	Output PCM buffer

§ PDMCC26XX_Handle

typedef PDMCC26XX_Config* PDMCC26XX_Handle

A handle that is returned from a PDMCC26XX_open() call.

§ PDMCC26XX_CallbackFxn

typedef void(* PDMCC26XX_CallbackFxn) (PDMCC26XX_Handle handle, PDMCC26XX_StreamNotification *streamNotification)

The definition of a callback function used when buffers are ready.

Parameters

PDMCC26XX_Handle PDMCC26XX_Handle

Enumeration Type Documentation

§ PDMCC26XX_Status

enum PDMCC26XX_Status

Status codes that are set by the PDM driver.

Enumerator
PDMCC26XX_STREAM_IDLE	Idle mode. Stream not started
PDMCC26XX_STREAM_BLOCK_READY	Buffer ready
PDMCC26XX_STREAM_BLOCK_READY_BUT_PDM_OVERFLOW	Buffer ready, but the I2S module has had to drop data .
PDMCC26XX_STREAM_ERROR	The I2S module encountered a hardware error. Likely because the target address for the I2S DMA was NULL
PDMCC26XX_STREAM_STOPPING	A stop was requested and this is the last buffer to be produced.
PDMCC26XX_STREAM_STOPPED	Unused
PDMCC26XX_STREAM_FAILED_TO_STOP	Buffer ready

§ PDMCC26XX_PcmSampleRate

enum PDMCC26XX_PcmSampleRate

PCM output sample rates supported by the driver.

The driver will default to 16kHz output. Switching to 8kHz switches the signal processing chain used internally.

Enumerator
PDMCC26XX_PCM_SAMPLE_RATE_16K
PDMCC26XX_PCM_SAMPLE_RATE_8K

§ PDMCC26XX_Gain

enum PDMCC26XX_Gain

Predefined gain settings.

Gain is controlled by modifying the first coefficient of the PDM filter. Use these defines to set the correct gain setting in the default filter. This setting does not affect any non-default filters! All values are in dB. Default prefilter stages will add 12dB gain. PDM2PCM algorithm returns false if any of the samples decimated goes above 2^16 - 1, i.e. the sample clipped during decimation. This information can be used for automatic gain control.

Enumerator
PDMCC26XX_GAIN_24	24dB gain
PDMCC26XX_GAIN_18	18dB gain
PDMCC26XX_GAIN_12	12dB gain. Default
PDMCC26XX_GAIN_6	6dB gain
PDMCC26XX_GAIN_0	0dB gain
PDMCC26XX_GAIN_END	Internal use only

Function Documentation

§ PDMCC26XX_init()

void PDMCC26XX_init ( PDMCC26XX_Handle handle )

PDM CC26XX initialization.

§ PDMCC26XX_open()

PDMCC26XX_Handle PDMCC26XX_open ( PDMCC26XX_Params * params )

Function to initialize the CC26XX PDM peripheral specified by the particular handle. The parameter specifies which mode the PDM will operate.

The function will set a dependency on the PDM module, which in turn powers up the module and enables the clock. IOs are also allocated, however the PDM driver will not begin streaming audio until PDMCC26XX_startStream() is called.

Precondition: PDM controller has been initialized

Parameters

params Pointer to a parameter block. Will use default parameters if NULL

Returns: A PDMCC26XX_Handle on success or a NULL on an error or if it has been already opened

See also: PDMCC26XX_close()

§ PDMCC26XX_close()

void PDMCC26XX_close ( PDMCC26XX_Handle handle )

Function to close a given CC26XX PDM peripheral specified by the PDM handle.

Posts an event that shuts down the I2S hardware, frees all memory used by the driver on the heap, releases the pins back to the PIN driver, and releases the dependency on the corresponding power domain.

Precondition: PDMCC26XX_open() has to be called first.

Postcondition: The PDM task must be allowed to run to synchronously shut down the driver

Parameters

handle A PDMCC26XX_Handle returned from PDMCC26XX_open()

See also: PDMCC26XX_open

§ PDMCC26XX_startStream()

bool PDMCC26XX_startStream ( PDMCC26XX_Handle handle )

Function to start streaming PDM data.

Posts an event that tells the I2S hardware to start streaming and the PDM task to start processing incoming data.

Precondition: PDMCC26XX_open() has to be called first.; The device must be deriving SCLK_HF from XOSC_HF or noise performance will be significantly degraded.

Postcondition: The PDM task must be allowed to run (by e.g. pending on a semaphore in the application task) to process incoming PDM data from the I2S module.

Parameters

handle A PDM handle returned from PDMCC26XX_open()

Returns: true if transfer is successful and false if not

See also: PDMCC26XX_open(), PDMCC26XX_stopStream()

§ PDMCC26XX_stopStream()

bool PDMCC26XX_stopStream ( PDMCC26XX_Handle handle )

Function to stop streaming PDM data.

Blocks while the I2S module shuts down gracefully. Subsequently posts an event to let the PDM task process any remaining data.

Precondition: PDMCC26XX_startStream() has to be called first.

Parameters

handle A PDM handle returned from PDMCC26XX_open()

Returns: True if stream stopped successfully and false if not

Postcondition: Process all available PCM buffers by calling PDMCC26XX_requestBuffer() until it returns false. Otherwise, the available PCM buffers will take up space on the heap until PDMCC26XX_close() or PDMCC26XX_startStream() are called.

See also: PDMCC26XX_open(), PDMCC26XX_startStream()

§ PDMCC26XX_requestBuffer()

bool PDMCC26XX_requestBuffer	(	PDMCC26XX_Handle	handle,
		PDMCC26XX_BufferRequest *	bufferRequest
	)

Function for requesting buffer.

PDMCC26XX_requestBuffer returns immediately even if no buffer is available. The caller is notified through events each time a buffer is available. However, more than one buffer may be available. Hence, the caller should request even without notification if the caller is ready to process.

Precondition: PDMCC26XX_open() and PDMCC26XX_startStream() has to be called first.

Parameters

handle	A PDM handle returned from PDMCC26XX_open()
*bufferRequest	Pointer to PDMCC26XX_BufferRequest struct

Returns: True if request is successful and false if not

See also: PDMCC26XX_open(), PDMCC26XX_startStream()

§ PDMCC26XX_Params_init()

void PDMCC26XX_Params_init ( PDMCC26XX_Params * params )

Variable Documentation

§ PDMCC26XX_config

const PDMCC26XX_Config PDMCC26XX_config[]

PDMCC26XX_Config struct defined in the board file

Detailed Description

Overview

General Behaviour

Error Handling

Heap Full

PDM Task Not Serviced In Time

PDMCC26XX_open Failing

PDMCC26XX_startStream Failing

PDMCC26XX_stopStream Failing

Power Management

Standard Use Case

8kHz PCM output

Data Structures

Macros

Typedefs

Enumerations

Functions

Variables

Macro Definition Documentation

§ PDM_TASK_STACK_SIZE

§ PCM_SAMPLE_SIZE

§ PCM_COMPRESSION_RATE

§ MINIMUM_PDM_BUFFER_QUEUE_DEPTH

§ PCM_METADATA_SIZE

Typedef Documentation

§ PDMCC26XX_MallocFxn

§ PDMCC26XX_FreeFxn

§ PDMCC26XX_Pdm2PcmFxn

§ PDMCC26XX_Handle

§ PDMCC26XX_CallbackFxn

Enumeration Type Documentation

§ PDMCC26XX_Status

§ PDMCC26XX_PcmSampleRate

§ PDMCC26XX_Gain

Function Documentation

§ PDMCC26XX_init()

§ PDMCC26XX_open()

§ PDMCC26XX_close()

§ PDMCC26XX_startStream()

§ PDMCC26XX_stopStream()

§ PDMCC26XX_requestBuffer()

§ PDMCC26XX_Params_init()

Variable Documentation

§ PDMCC26XX_config