nRF5 PDM microphone

Microphone implementation for the nRF5 PDM peripheral. More...

Data Structures
struct	MicDevice
	nRF5 PDM microphone device. More...

Macros
#define	PDM_BUFFER_SIZE_SAMPLES   (320)
	Samples per PDM DMA buffer.
#define	PDM_BUFFER_COUNT   (2)
	Number of PDM DMA buffers.
#define	PDM_GAIN_DEFAULT   (NRF_PDM_GAIN_DEFAULT)
	Default PDM gain.
#define	CIRCULAR_BUF_SIZE_MS   (320)
	Preferred length of the queue between DMA and the data handler, in milliseconds.
#define	CIRCULAR_BUF_SIZE_SAMPLES   ((MIC_SAMPLE_RATE * CIRCULAR_BUF_SIZE_MS) / 1000)
	Preferred queue length, in samples.
#define	CIRCULAR_BUF_SIZE_BYTES   (CIRCULAR_BUF_SIZE_SAMPLES * sizeof(int16_t))
	Preferred queue size, in bytes.
#define	CIRCULAR_BUF_MIN_SIZE_MS   (128)
	Minimum queue length, in milliseconds, accepted when the heap is too fragmented for the preferred one.
#define	CIRCULAR_BUF_MIN_SIZE_SAMPLES   ((MIC_SAMPLE_RATE * CIRCULAR_BUF_MIN_SIZE_MS) / 1000)
	Minimum queue length, in samples.
#define	CIRCULAR_BUF_MIN_SIZE_BYTES   (CIRCULAR_BUF_MIN_SIZE_SAMPLES * sizeof(int16_t))
	Minimum queue size, in bytes.
#define	CIRCULAR_BUF_STEP_MS   (32)
	Queue shrink per allocation retry, in milliseconds.
#define	CIRCULAR_BUF_STEP_SAMPLES   ((MIC_SAMPLE_RATE * CIRCULAR_BUF_STEP_MS) / 1000)
	Queue shrink per allocation retry, in samples.
#define	CIRCULAR_BUF_STEP_BYTES   (CIRCULAR_BUF_STEP_SAMPLES * sizeof(int16_t))
	Queue shrink per allocation retry, in bytes.

Detailed Description

Microphone implementation for the nRF5 PDM peripheral.

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Data Structure Documentation

MicDevice

struct MicDevice

nRF5 PDM microphone device.

SF32LB52 PDM microphone device.

QEMU microphone device.

Data Fields
uint32_t	channel_depth	PDM channel depth in bits.
uint32_t	channels	Number of channels, 1 or 2. Number of channels.
Pinmux	clk_gpio	PDM clock pin.
uint32_t	clk_pin	PDM clock pin.
Pinmux	data_gpio	PDM data pin.
uint32_t	data_pin	PDM data pin.
uint16_t	default_volume	Default volume scalar (max 128); not used by the driver.
IRQn_Type	pdm_dma_irq	PDM DMA interrupt.
const nrfx_pdm_t	pdm_instance	PDM instance.
PDM_TypeDef *	pdm_instance	PDM instance.
IRQn_Type	pdm_irq	PDM interrupt.
uint32_t	sample_rate	PDM sample rate in Hz.
MicDeviceState *	state	Driver runtime state.

Macro Definition Documentation

CIRCULAR_BUF_MIN_SIZE_BYTES

#define CIRCULAR_BUF_MIN_SIZE_BYTES   (CIRCULAR_BUF_MIN_SIZE_SAMPLES * sizeof(int16_t))

Minimum queue size, in bytes.

CIRCULAR_BUF_MIN_SIZE_MS

#define CIRCULAR_BUF_MIN_SIZE_MS   (128)

Minimum queue length, in milliseconds, accepted when the heap is too fragmented for the preferred one.

Transcription quality degrades noticeably below it.

CIRCULAR_BUF_MIN_SIZE_SAMPLES

#define CIRCULAR_BUF_MIN_SIZE_SAMPLES   ((MIC_SAMPLE_RATE * CIRCULAR_BUF_MIN_SIZE_MS) / 1000)

Minimum queue length, in samples.

CIRCULAR_BUF_SIZE_BYTES

#define CIRCULAR_BUF_SIZE_BYTES   (CIRCULAR_BUF_SIZE_SAMPLES * sizeof(int16_t))

Preferred queue size, in bytes.

CIRCULAR_BUF_SIZE_MS

#define CIRCULAR_BUF_SIZE_MS   (320)

Preferred length of the queue between DMA and the data handler, in milliseconds.

CIRCULAR_BUF_SIZE_SAMPLES

#define CIRCULAR_BUF_SIZE_SAMPLES   ((MIC_SAMPLE_RATE * CIRCULAR_BUF_SIZE_MS) / 1000)

Preferred queue length, in samples.

CIRCULAR_BUF_STEP_BYTES

#define CIRCULAR_BUF_STEP_BYTES   (CIRCULAR_BUF_STEP_SAMPLES * sizeof(int16_t))

Queue shrink per allocation retry, in bytes.

CIRCULAR_BUF_STEP_MS

#define CIRCULAR_BUF_STEP_MS   (32)

Queue shrink per allocation retry, in milliseconds.

Gives about 7 attempts between the preferred and the minimum length.

CIRCULAR_BUF_STEP_SAMPLES

#define CIRCULAR_BUF_STEP_SAMPLES   ((MIC_SAMPLE_RATE * CIRCULAR_BUF_STEP_MS) / 1000)

Queue shrink per allocation retry, in samples.

PDM_BUFFER_COUNT

#define PDM_BUFFER_COUNT   (2)

Number of PDM DMA buffers.

PDM_BUFFER_SIZE_SAMPLES

#define PDM_BUFFER_SIZE_SAMPLES   (320)

Samples per PDM DMA buffer.

PDM_GAIN_DEFAULT

#define PDM_GAIN_DEFAULT   (NRF_PDM_GAIN_DEFAULT)

Default PDM gain.