Detailed Description

PDM driver implementation for a CC26XX PDM controller.

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

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

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)

This 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.

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.

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.

While using PDM on CC26XX:

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 around 2ms, unless an error occurs. The system is allowed to enter standby again after PDMCC26XX_stopStream() is called.

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.

Lost Frames

If the application fails to consume buffers in a timely manner and consequently the heap is full when driver tries to allocate a new buffer for new incoming data, 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.

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

PDMCC26XX_stopStream Failing

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

The driver is not currently streaming
The I2S driver could not gracefully shut down

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.

Supported Functions

API function	Description
PDMCC26XX_init()	Initialize PDM driver
PDMCC26XX_open()	Set system dependencies, configure pins
PDMCC26XX_startStream()	Turn on mic, start stream and prevent standby
PDMCC26XX_stopStream()	Stop stream and release standby hold, turn off mic
PDMCC26XX_requestBuffer()	Request a buffer from the driver
PDMCC26XX_close()	Disable HW and release system dependencies

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 *pStreamNotification)
{
    PDMCC26XX_Status streamStatus = pStreamNotification->status;
    if (streamStatus == PDMCC26XX_STREAM_BLOCK_READY || streamStatus == PDMCC26XX_STREAM_BLOCK_READY_BUT_PDM_OVERFLOW){
        Semaphore_post(Semaphore_handle(&bufferReadySemaphore));
    }
    else {
        // Handle the error
    }
}
static void applicationTask(UArg a0, UArg a1){
    Semaphore_Params semParams;
    PDMCC26XX_BufferRequest bufferRequest;
    const uint16_t returnBufferSize = 64;
    const uint8_t numberOfPcmBuffersToRequest = 128;
    // Initialize semaphore
    Semaphore_Params_init(&semParams);
    semParams.mode = Semaphore_Mode_BINARY;
    Semaphore_construct(&bufferReadySemaphore, 0, &semParams);
    // Set up parameters for PDM streaming with compression
    PDMCC26XX_Params pdmParams = {
        .callbackFxn = bufRdy_callback,
        .useDefaultFilter = true,
        .decimationFilter = NULL,
        .micGain = PDMCC26XX_GAIN_12,
        .micPowerActiveHigh = true,
        .applyCompression = true,
        .startupDelayWithClockInSamples = 0,
        .retBufSizeInBytes = returnBufferSize,
        .mallocFxn = &malloc,
        .freeFxn = &free,
        .custom = NULL
    };
    // 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
            Semaphore_pend(Semaphore_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
    }
}

Instrumentation

The PDM driver interface produces log statements if instrumentation is enabled.

Instrumentation	Description
Diags_USER1	Logs the start and end of each API call of the PDM driver and progress through events
Diags_USER2	Logs occurances in the I2S sub-module of the PDM driver
Warnings	Logs unexpected events such as initialisations or memory allocations failing

#include <ti/sysbios/knl/Semaphore.h>
#include <ti/drivers/PIN.h>
#include <ti/sysbios/family/arm/m3/Hwi.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	ti_sysbios_family_arm_m3_Hwi__nolocalnames

#define	PDM_TASK_STACK_SIZE 500

#define	PDM_NUM_OF_CHANNELS 2

#define	PDM_BLOCK_SIZE_IN_SAMPLES 64

#define	PDM_BUFFER_SIZE_IN_BLOCKS 3

#define	PCM_COMPRESSION_RATE 4

#define	PCM_METADATA_SIZE 4

#define	PDM_SAMPLE_SIZE 16

#define	PCM_SAMPLE_SIZE 16

#define	PDM_NUMBER_OF_PINS 1

#define	PDM_EVT_BLK_RDY Event_Id_00

#define	PDM_EVT_START Event_Id_01

#define	PDM_EVT_BLK_ERROR Event_Id_02

#define	PDM_EVT_CLOSE Event_Id_03

#define	PDM_DECIMATION_STARTUP_DELAY_IN_SAMPLES 32

#define	PDM_ROLLBACK_OPEN 1 << 0

#define	PDM_ROLLBACK_ACTIVE_PCM_BUFFER 1 << 1

#define	PDM_ROLLBACK_I2S_DRIVER 1 << 2

#define	PDM_ROLLBACK_PIN 1 << 3

#define	PDMCC26XX_COMPR_ITER_OUTPUT_SIZE 16

#define	PDMCC26XX_CPY_ITER_OUTPUT_SIZE 64

Typedefs
typedef uint16_t	pdmSample_t

typedef int16_t	pcmSample_t

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

typedef struct PDMCC26XX_HWAttrs	PDMCC26XX_HWAttrs
	PDMCC26XX Hardware attributes. More...

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

typedef enum PDMCC26XX_Status	PDMCC26XX_Status
	Status codes that are set by the PDM driver. More...

typedef enum PDMCC26XX_Gain	PDMCC26XX_Gain
	Predefined gain settings. More...

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

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

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

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

typedef struct PDMCC26XX_Object	PDMCC26XX_Object
	PDMCC26XX Object. 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_Gain { PDMCC26XX_GAIN_24, PDMCC26XX_GAIN_18, PDMCC26XX_GAIN_12, PDMCC26XX_GAIN_6, PDMCC26XX_GAIN_0, 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...

Variables
const PDMCC26XX_Config	PDMCC26XX_config []

Macro Definition Documentation

#define ti_sysbios_family_arm_m3_Hwi__nolocalnames

The following allows this header file to be included in an application file which also includes ti/sysbios/hal/Hwi.h.

#define PDM_TASK_STACK_SIZE 500

Defines TI-RTOS stack size allocation.

#define PDM_NUM_OF_CHANNELS 2

Use both word clock phases to get continuous PDM stream

Note: Internal use only

#define PDM_BLOCK_SIZE_IN_SAMPLES 64

PDM block size in number of 16bit samples. Each PDM sample actually consume 32 bits, given that we assume 16kHz sampling rate. Hence, the number of PDM samples are always twice the potential number of 16bit PCM samples.

Note: Internal use only

#define PDM_BUFFER_SIZE_IN_BLOCKS 3

PDM buffer size in number of blocks. We assume that we will be able to consume PDM samples in a timely manner. This allows us to use the minium number of blocks (3) for the PDMCC26XX driver.

#define PCM_COMPRESSION_RATE 4

Compression rate if compression is enabled

Note: Internal use only

#define PCM_METADATA_SIZE 4

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 differen information. The first byte is always an 8-bit sequence number.

Note: Internal use only

#define PDM_SAMPLE_SIZE 16

PDM sample size. Although there are 32 bits per sample at 16kHz we need to set it to 16 as part of the PDMCC26XX module configuration.

Note: Internal use only

#define PCM_SAMPLE_SIZE 16

PCM sample size in bits

Note: Internal use only since only 16 bits are supported

#define PDM_NUMBER_OF_PINS 1

Number of GPIOs used. When in debug mode 4 pins are used in addition to the pin to control power to the microphone.

Note: Internal use only

#define PDM_EVT_BLK_RDY Event_Id_00

PDM event set in the callback from the PDMCC26XX driver every time a block is ready for PDM2PCM conversion.

Note: Internal use only

#define PDM_EVT_START Event_Id_01

PDM event set to kick off stream from PDM thread context.

Note: Internal use only

#define PDM_EVT_BLK_ERROR Event_Id_02

PDM event set in the callback from the PDMCC26XX driver in case an error occurs.

Note: Internal use only

#define PDM_EVT_CLOSE Event_Id_03

PDM event set in the callback from the PDMCC26XX driver when the application calls PDMCC26XX_close().

Note: Internal use only

#define PDM_DECIMATION_STARTUP_DELAY_IN_SAMPLES 32

This value defines how many samples are discarded at minimum each time the PDM stream starts. The first few samples that are processed by the driver will not be representative of their actual value as the decimation filter has not sufficiently updated its internal state. A value < 8 is not reccomended, as the distortion of the signal is greatest there.

Note: Internal use only

#define PDM_ROLLBACK_OPEN 1 << 0

Reverses the driver being set to open in the object

Note: Internal use only

#define PDM_ROLLBACK_ACTIVE_PCM_BUFFER 1 << 1

Reverses the allocation of the activePcmBuffer

Note: Internal use only

#define PDM_ROLLBACK_I2S_DRIVER 1 << 2

Reverses the opening of the I2S driver

Note: Internal use only

#define PDM_ROLLBACK_PIN 1 << 3

Reverses the allocation of the PDM pin in the PIN driver

Note: Internal use only

#define PDMCC26XX_COMPR_ITER_OUTPUT_SIZE 16

Number of compressed bytes produced by each PDM->PCM conversion and compression

Note: Internal use only

#define PDMCC26XX_CPY_ITER_OUTPUT_SIZE 64

Number of uncompressed bytes produced by eahc PDM->PCM conversion and memcpy

Note: Internal use only

Typedef Documentation

typedef uint16_t pdmSample_t

PDM sample type. Prepared for future support of 24 sample size.

Note: Internal use only

typedef int16_t pcmSample_t

PCM sample type.

Note: Internal use only

typedef void*(* PDMCC26XX_MallocFxn) (size_t memSize)

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

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.

typedef struct PDMCC26XX_Config PDMCC26XX_Config

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

typedef struct PDMCC26XX_HWAttrs PDMCC26XX_HWAttrs

PDMCC26XX Hardware attributes.

These fields are used by the PDM driver

typedef struct PDMCC26XX_Config* PDMCC26XX_Handle

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

typedef enum PDMCC26XX_Status PDMCC26XX_Status

Status codes that are set by the PDM driver.

typedef enum PDMCC26XX_Gain PDMCC26XX_Gain

Predefined gain settings.

Gain is controlled by modifying the first coefficient of the PDM filter. Use these defines to get correct gain setting. All these values are in dB. Default filter will add 12dB gain. In fact this is not an amplification, this setting uses all the information in the PDM samples, so if use case allows it this will have the least compromised range. PDM2PCM algotrithm 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.

typedef struct PDMCC26XX_StreamNotification PDMCC26XX_StreamNotification

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

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

typedef struct PDMCC26XX_BufferRequest PDMCC26XX_BufferRequest

A PDMCC26XX_BufferRequest data structure is used with PDMCC26XX_requestBuffer().

buffer is a pointer to the requested buffer. It is NULL if no buffer is available. Each buffer contains a metadata header of size PCM_METADATA_SIZE. The first byte of the metadata is always an 8 bit sequence number. The other bytes depends on mode.

Mode	Interpretation of bufferIn being NULL after returning
Blocking mode	Request timed out and still no buffer available
Non-Blocking mode	No buffer available

typedef struct PDMCC26XX_Params PDMCC26XX_Params

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

See also: PDMCC26XX_Params_init

typedef struct PDMCC26XX_Object PDMCC26XX_Object

PDMCC26XX Object.

The application must not access any member variables of this structure!

Enumeration Type Documentation

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 PDMCC26XX driver is impending failure if not serviced in time. Stream is likely to stop now.
PDMCC26XX_STREAM_ERROR	Driver error
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

enum PDMCC26XX_Gain

Predefined gain settings.

Gain is controlled by modifying the first coefficient of the PDM filter. Use these defines to get correct gain setting. All these values are in dB. Default filter will add 12dB gain. In fact this is not an amplification, this setting uses all the information in the PDM samples, so if use case allows it this will have the least compromised range. PDM2PCM algotrithm 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

void PDMCC26XX_init ( PDMCC26XX_Handle handle )

PDM CC26XX initialization.

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()

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

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.

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()

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()

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()

Variable Documentation

const PDMCC26XX_Config PDMCC26XX_config[]

PDMCC26XX_Config struct defined in the board file

Detailed Description

Overview

General Behaviour

Error Handling

Lost Frames

PDMCC26XX_open Failing

PDMCC26XX_startStream Failing

PDMCC26XX_stopStream Failing

Power Management

Supported Functions

Standard Use Case

Instrumentation

Data Structures

Macros

Typedefs

Enumerations

Functions

Variables

Macro Definition Documentation

Typedef Documentation

Enumeration Type Documentation

Function Documentation

Variable Documentation