PDM - Pulse Density Modulation

Description

Pulse Density Modulation (PDM) peripheral API.

PDM API functions provide full support for the PDM peripheral. The PDM peripheral accepts PDM bitstreams and produces PCM encoded output.

The following is an example PDM usage when interfacing to two PDM microphones:

Configure clocks and GPIO pins:

PDM_Init_TypeDef pdmInit = PDM_INIT_DEFAULT ;
CMU_DPLLInit_TypeDef pllInit = CMU_DPLL_LFXO_TO_40MHZ ;
CMU_OscillatorEnable ( cmuOsc_LFXO , true , true );
// Lock PLL to 1,411,209 Hz to achieve 44,100 kHz PCM sampling rate
// when using 32x PDM oversampling
pllInit. frequency = 1411209;
pllInit. m = 14;
pllInit. n = 645;
CMU_DPLLLock (&pllInit);
// Setup all GPIO's.
GPIO_PinModeSet (MIC_CLK_PORT, MIC_CLK_PIN, gpioModePushPull , 0);
GPIO_PinModeSet (MIC_DATA_PORT, MIC_DATA_PIN, gpioModeInput , 0);
// Set fast slew rate on PDM mic CLK and DATA pins
GPIO_SlewrateSet (MIC_CLK_PORT, 7U, 7U);
// Enable PDM peripheral clock.
CMU_ClockEnable ( cmuClock_PDM , true );
// Select PDM reference clock source and enable it.
CMU_ClockSelectSet ( cmuClock_PDMREF , cmuSelect_HFRCO);
CMU_ClockEnable ( cmuClock_PDMREF , true );
// Route PDM signals to correct GPIO's.
PDM->ROUTELOC0 = (PDM->ROUTELOC0 & ~_PDM_ROUTELOC0_DAT0LOC_MASK)
| (MIC_DATA_PDM_LOC << _PDM_ROUTELOC0_DAT0LOC_SHIFT);
PDM->ROUTELOC1 = MIC_CLK_PDM_LOC << _PDM_ROUTELOC1_CLKLOC_SHIFT;
PDM->ROUTEPEN |= PDM_ROUTEPEN_CLKPEN | PDM_ROUTEPEN_DAT0PEN;

Initialize and start PDM, then read PCM samples from FIFO:

PDM_Init_TypeDef init = PDM_INIT_DEFAULT ;
PDM_Init (PDM, &init);
while ( true ) {
*pBuffer++ = PDM_Rx (PDM);
}

Data Structures

struct PDM_Init_TypeDef
PDM initialization structure.

Functions

void PDM_DeInit (PDM_TypeDef *pdm)
De-initialize the PDM peripheral.
void PDM_Init (PDM_TypeDef *pdm, const PDM_Init_TypeDef *init)
Initialize the PDM peripheral.
void PDM_Reset (PDM_TypeDef *pdm)
Initialize PDM registers with reset values.
void PDM_Clear (PDM_TypeDef *pdm)
Clear the PDM filter.
void PDM_FifoFlush (PDM_TypeDef *pdm)
Flush the PDM sample FIFO.
void PDM_IntClear (PDM_TypeDef *pdm, uint32_t flags)
Clear one or more pending PDM interrupts.
void PDM_IntDisable (PDM_TypeDef *pdm, uint32_t flags)
Disable one or more PDM interrupts.
void PDM_IntEnable (PDM_TypeDef *pdm, uint32_t flags)
Enable one or more PDM interrupts.
uint32_t PDM_IntGet (PDM_TypeDef *pdm)
Get pending PDM interrupt flags.
uint32_t PDM_IntGetEnabled (PDM_TypeDef *pdm)
Get enabled and pending PDM interrupt flags.
void PDM_IntSet (PDM_TypeDef *pdm, uint32_t flags)
Set one or more pending PDM interrupts.
uint32_t PDM_Rx (PDM_TypeDef *pdm)
Read one entry from the PDM FIFO.
void PDM_Start (PDM_TypeDef *pdm)
Start the PDM operation (start the PDM filter).
uint32_t PDM_StatusGet (PDM_TypeDef *pdm)
Get the PDM STATUS register.
void PDM_Stop (PDM_TypeDef *pdm)
Stop the PDM operation (stop the PDM filter).

Macros

#define PDM_INIT_DEFAULT
Default configuration for PDM.

Enumerations

enum PDM_Ch1ClkPolarity_Typedef {
pdmCh1ClkPolarityRisingEdge = _PDM_CFG0_CH1CLKPOL_NORMAL,
pdmCh1ClkPolarityFallingEdge = _PDM_CFG0_CH1CLKPOL_INVERT
}
Configure CH1 CLK Polarity.
enum PDM_Ch0ClkPolarity_Typedef {
pdmCh0ClkPolarityRisingEdge = _PDM_CFG0_CH0CLKPOL_NORMAL,
pdmCh0ClkPolarityFallingEdge = _PDM_CFG0_CH0CLKPOL_INVERT
}
Configure CH0 CLK Polarity.
enum PDM_FifoValidWatermark_Typedef {
pdmFifoValidWatermarkOne = _PDM_CFG0_FIFODVL_ONE,
pdmFifoValidWatermarkTwo = _PDM_CFG0_FIFODVL_TWO,
pdmFifoValidWatermarkThree = _PDM_CFG0_FIFODVL_THREE,
pdmFifoValidWatermarkFour = _PDM_CFG0_FIFODVL_FOUR
}
Configure FIFO Data valid level water-mark.
enum PDM_DataFormat_TypeDef {
pdmDataFormatRight16 = _PDM_CFG0_DATAFORMAT_RIGHT16,
pdmDataFormatDouble16 = _PDM_CFG0_DATAFORMAT_DOUBLE16,
pdmDataFormatRight24 = _PDM_CFG0_DATAFORMAT_RIGHT24,
pdmDataFormatFull32bit = _PDM_CFG0_DATAFORMAT_FULL32BIT,
pdmDataFormatLeft16 = _PDM_CFG0_DATAFORMAT_LEFT16,
pdmDataFormatLeft24 = _PDM_CFG0_DATAFORMAT_LEFT24,
pdmDataFormatRaw32bit = _PDM_CFG0_DATAFORMAT_RAW32BIT
}
Configure PDM filter data output format.
enum PDM_NumberOfChannels_TypeDef {
pdmNumberOfChannelsOne = _PDM_CFG0_NUMCH_ONE,
pdmNumberOfChannelsTwo = _PDM_CFG0_NUMCH_TWO
}
Configure number of PDM channels.
enum PDM_FilterOrder_TypeDef {
pdmFilterOrderSecond = _PDM_CFG0_FORDER_SECOND,
pdmFilterOrderThird = _PDM_CFG0_FORDER_THIRD,
pdmFilterOrderFourth = _PDM_CFG0_FORDER_FOURTH,
pdmFilterOrderFifth = _PDM_CFG0_FORDER_FIFTH
}
Configure order of the PDM filter.

Function Documentation

◆ PDM_DeInit()

void PDM_DeInit ( PDM_TypeDef * pdm )

De-initialize the PDM peripheral.

This function will stop the PDM filter and set PDM control registers to their reset values.

Parameters
[in] pdm A pointer to the PDM peripheral register block.

◆ PDM_Init()

void PDM_Init ( PDM_TypeDef * pdm,
const PDM_Init_TypeDef * init
)

Initialize the PDM peripheral.

This function will configure basic settings in PDM according to values in the initialization data structure.

Notice that enabling of PDM clock, setup of PDM pins and setup of PRS is not covered by this function.

Parameters
[in] pdm A pointer to the PDM peripheral register block.
[in] init A pointer to the initialization structure used to configure the PDM.

◆ PDM_Reset()

void PDM_Reset ( PDM_TypeDef * pdm )

Initialize PDM registers with reset values.

Parameters
[in] pdm A pointer to the PDM peripheral register block.

◆ PDM_Clear()

void PDM_Clear ( PDM_TypeDef * pdm )
inline

Clear the PDM filter.

Parameters
[in] pdm A pointer to the PDM peripheral register block.

◆ PDM_FifoFlush()

void PDM_FifoFlush ( PDM_TypeDef * pdm )
inline

Flush the PDM sample FIFO.

Parameters
[in] pdm A pointer to the PDM peripheral register block.

◆ PDM_IntClear()

void PDM_IntClear ( PDM_TypeDef * pdm,
uint32_t flags
)
inline

Clear one or more pending PDM interrupts.

Parameters
[in] pdm A pointer to the PDM peripheral register block.
[in] flags Pending PDM interrupt sources to clear. Use one or more valid interrupt flags for the PDM module. The flags are PDM_IFC_DV, PDM_IFC_DVL, PDM_IFC_OF and PDM_IFC_UF.

◆ PDM_IntDisable()

void PDM_IntDisable ( PDM_TypeDef * pdm,
uint32_t flags
)
inline

Disable one or more PDM interrupts.

Parameters
[in] pdm A pointer to the PDM peripheral register block.
[in] flags PDM interrupt sources to disable. Use one or more valid interrupt flags for the PDM module. The flags are PDM_IEN_DV, PDM_IEN_DVL, PDM_IEN_OF and PDM_IEN_UF.

◆ PDM_IntEnable()

void PDM_IntEnable ( PDM_TypeDef * pdm,
uint32_t flags
)
inline

Enable one or more PDM interrupts.

Note
Depending on the use, a pending interrupt may already be set prior to enabling the interrupt. To ignore a pending interrupt, consider using PDM_IntClear() prior to enabling the interrupt.
Parameters
[in] pdm A pointer to the PDM peripheral register block.
[in] flags PDM interrupt sources to enable. Use one or more valid interrupt flags for the PDM module. The flags are PDM_IEN_DV, PDM_IEN_DVL, PDM_IEN_OF and PDM_IEN_UF.

◆ PDM_IntGet()

uint32_t PDM_IntGet ( PDM_TypeDef * pdm )
inline

Get pending PDM interrupt flags.

Note
Event bits are not cleared by the use of this function.
Parameters
[in] pdm A pointer to the PDM peripheral register block.
Returns
PDM interrupt sources pending. Returns one or more valid interrupt flags for PDM module. The flags are PDM_IF_DV, PDM_IF_DVL, PDM_IF_OF and PDM_IF_UF.

◆ PDM_IntGetEnabled()

uint32_t PDM_IntGetEnabled ( PDM_TypeDef * pdm )
inline

Get enabled and pending PDM interrupt flags.

Useful for handling more interrupt sources in the same interrupt handler.

Note
Interrupt flags are not cleared by the use of this function.
Parameters
[in] pdm A pointer to the PDM peripheral register block.
Returns
Pending and enabled PDM interrupt sources Return value is the bitwise AND of
  • the enabled interrupt sources in PDM_IEN and
  • the pending interrupt flags PDM_IF

◆ PDM_IntSet()

void PDM_IntSet ( PDM_TypeDef * pdm,
uint32_t flags
)
inline

Set one or more pending PDM interrupts.

Parameters
[in] pdm A pointer to the PDM peripheral register block.
[in] flags PDM interrupt sources to set to pending. Use one or more valid interrupt flags for the PDM module. The flags are PDM_IFS_DV, PDM_IFS_DVL, PDM_IFS_OF and PDM_IFS_UF.

◆ PDM_Rx()

uint32_t PDM_Rx ( PDM_TypeDef * pdm )
inline

Read one entry from the PDM FIFO.

Note
This function will wait until a sample is available in the FIFO. Depending on PDM configuration, a FIFO entry can consist of one or two samples.
Parameters
[in] pdm A pointer to the PDM peripheral register block.
Returns
The entry read from the FIFO.

◆ PDM_Start()

void PDM_Start ( PDM_TypeDef * pdm )
inline

Start the PDM operation (start the PDM filter).

Parameters
[in] pdm A pointer to the PDM peripheral register block.

◆ PDM_StatusGet()

uint32_t PDM_StatusGet ( PDM_TypeDef * pdm )
inline

Get the PDM STATUS register.

Parameters
[in] pdm A pointer to the PDM peripheral register block.
Returns
STATUS register value.

◆ PDM_Stop()

void PDM_Stop ( PDM_TypeDef * pdm )
inline

Stop the PDM operation (stop the PDM filter).

Parameters
[in] pdm A pointer to the PDM peripheral register block.

Macro Definition Documentation

◆ PDM_INIT_DEFAULT

#define PDM_INIT_DEFAULT
Value:
{ \
true, /* Start PDM filter after initialization. */ \
32U, /* PDM down sampling rate. */ \
5U, /* PDM gain. */ \
pdmCh1ClkPolarityFallingEdge, /* Input data clocked on falling clock edge. */ \
pdmCh0ClkPolarityRisingEdge, /* Input data clocked on rising clock edge. */ \
true, /* Enable stereo mode for channel pair CH0 and CH1. */ \
pdmFifoValidWatermarkOne, /* At least one word water-mark level. */ \
pdmDataFormatDouble16, /* Two 16-bit samples per FIFO entry. */ \
pdmNumberOfChannelsTwo, /* Two Channels. */ \
pdmFilterOrderFifth, /* Fifth order filter. */ \
0U /* No clock prescaling. */ \
}

Default configuration for PDM.

Stereo Ch0/1, 16bit samples, 44,100 Hz sampling rate, 32 times oversampling (requires 1,411,209 Hz PDM clock).

Enumeration Type Documentation

◆ PDM_Ch1ClkPolarity_Typedef

enum PDM_Ch1ClkPolarity_Typedef

Configure CH1 CLK Polarity.

Enumerator
pdmCh1ClkPolarityRisingEdge

Input data clocked on rising clock edge.

pdmCh1ClkPolarityFallingEdge

Input data clocked on falling clock edge.

◆ PDM_Ch0ClkPolarity_Typedef

enum PDM_Ch0ClkPolarity_Typedef

Configure CH0 CLK Polarity.

Enumerator
pdmCh0ClkPolarityRisingEdge

Input data clocked on rising clock edge.

pdmCh0ClkPolarityFallingEdge

Input data clocked on falling clock edge.

◆ PDM_FifoValidWatermark_Typedef

enum PDM_FifoValidWatermark_Typedef

Configure FIFO Data valid level water-mark.

Enumerator
pdmFifoValidWatermarkOne

At least one word.

pdmFifoValidWatermarkTwo

Two words.

pdmFifoValidWatermarkThree

Three words.

pdmFifoValidWatermarkFour

Four words.

◆ PDM_DataFormat_TypeDef

enum PDM_DataFormat_TypeDef

Configure PDM filter data output format.

Enumerator
pdmDataFormatRight16

Right aligned 16-bit, left bits are sign extended.

pdmDataFormatDouble16

Pack two 16-bit samples into one 32-bit word.

pdmDataFormatRight24

Right aligned 24bit, left bits are sign extended.

pdmDataFormatFull32bit

32 bit data.

pdmDataFormatLeft16

Left aligned 16-bit, right bits are zeros.

pdmDataFormatLeft24

Left aligned 24-bit, right bits are zeros.

pdmDataFormatRaw32bit

RAW 32 bit data from integrator.

◆ PDM_NumberOfChannels_TypeDef

enum PDM_NumberOfChannels_TypeDef

Configure number of PDM channels.

Enumerator
pdmNumberOfChannelsOne

Only one Channel.

pdmNumberOfChannelsTwo

Two Channels.

◆ PDM_FilterOrder_TypeDef

enum PDM_FilterOrder_TypeDef

Configure order of the PDM filter.

Enumerator
pdmFilterOrderSecond

Second order filter.

pdmFilterOrderThird

Third order filter.

pdmFilterOrderFourth

Fourth order filter.

pdmFilterOrderFifth

Fifth order filter.