PDM

概述

PDM 是对连续变化的模拟信号进行抽样、量化和编码产生的数字信号的信号调制方式。

PDM 通过合适的算法将典型的 24 比特的脉冲编码调制（Pulse Code Modulation，PCM）信号转换为 1 比特的音频信号，其为 1 位数字采样的高频数据流，脉冲的相对密度对应于模拟信号的幅度。原理图如下：

PDM SAMPLE 架构图

在 PDM 信号中，脉冲的相对密度对应于模拟信号的幅度。大量的 ‘1’ 对应于高（正）幅度值，而大量的 ‘0’ 对应于低（负）幅度值，交替的 ‘1’ 与 ‘0’ 对应于幅度值 ‘0’。

WQ7036 有 4 个 PDM Rx 模块和 1 个 PDM Tx 模块，支持最多 4 对（或 8 路）1 比特 PDM 格式数字信号输入和 1 对（或 2 路）1 比特 PDM 格式数字信号输出。每个 PDM 模块可以工作在不同时钟。

功能特性

PDM 模块特性如下：

支持双声道数据输入/输出，即上升沿（左声道），下降沿（右声道）。
支持 Tx/Rx 配置成 master 或者 slave。
master 模式下，输出时钟为 audio 工作时钟整数倍分频。
支持输入/输出数据时延配置（0~3 拍）。
支持 Tx/Rx 独立运行。
支持 4 MHz、3.2 MHz、2 MHz、1 MHz 等采样率（audio 工作时钟为 16 MHz）。
支持 3.84 MHz、3.072 MHz、1.92 MHz、1.56 MHz、0.96 MHz 等采样率（audio 工作时钟为 15.36 MHz）。

PDM RX 架构

PDM RX 的架构图如下图所示。

PDM RX 架构图

一个 PDM Rx 模块可以支持两路 PDM 数据传输和单路 PDM 数据传输：

两路数据传输时，在时钟上升沿和下降沿进行数据分离，得到两路独立的数字信号，再分别进行下采样和滤波处理，得到多比特高精度音频信号。
单路数据传输时，在任意时钟沿（上升沿或下降沿）提取数据，再分别进行下采样和滤波处理，得到多比特高精度音频信号。

WQ7036 最大支持 8 路 PDM MIC 数据输入。

PDM TX 架构

PDM TX 架构图如下图所示。

PDM TX 架构图

WQ7036 支持两路 PDM 数据输出。两路 PCM 数据经过上采样和滤波等处理之后，经过 PDM Tx 模块得到两路 1 比特数字信号，在时钟上升沿和下降沿合并两路 1 比特数字信号，并输出到芯片 GPIO 管脚。

API 介绍

This section introduces the PDM module's enum, structure, functions and how to use this driver.

struct wq_pdm_gpio_cfg

Public Members

WQ_GPIO_ID clk: The gpio id used by pdm clk

WQ_GPIO_ID sd: The gpio id used by pdm data

struct wq_pdm_cfg

Public Members

WQ_PDM_FREQ_SAMPLE pdm_bck: PDM sample rate

bool pdm_slave: Is PDM in slave mode? True indicates slave mode, false indicates master mode

uint8_t pdm_phase: Value range 0~3, phase control achieved by controlling the delay of data sampling

wq_pdm_gpio_cfg_t pdm_gpio_cfg: GPIO configuration used by PDM

struct wq_pdm_rx_chn_cfg

Public Members

wq_rx_dfe_config_t dfe_cfg: Rxdfe receives pdm rx data, which is the relevant configuration of Rxdfe

WQ_AUDIO_TIMER_ID timer_id: Audio timer iid used by PDM RX

union wq_pdm_rx_en

Public Members

uint8_t pdm0_en: bit0: PDM_RX MODULE0 enable

uint8_t pdm1_en: bit1: PDM_RX MODULE1 enable

uint8_t pdm2_en: bit2: PDM_RX MODULE2 enable

uint8_t pdm3_en: bit3: PDM_RX MODULE3 enable

uint8_t reserved: bit4~bit7: reserve

struct wq_pdm_rx_en::[anonymous] _b

uint8_t bitmap

struct wq_pdm_rx_analog_param

Public Members

wq_pdm_rx_en_t pdm_en: PDM_RX MODULE enable bitmap

wq_mic_adc_micbias_u micbias: Micbias configuration corresponding to PDM RX module

wq_mic_adc_micbias_voltage_u micbias_voltage: Micbias voltage configuration corresponding to PDM RX module

Typedefs

typedef enum _WQ_PDM_PORT WQ_PDM_PORT: For specific definitions, please refer to the header file wq_audio_resource.h.

typedef enum _WQ_PDM_RX_CHANNEL WQ_PDM_RX_CHANNEL: For specific definitions, please refer to the header file wq_audio_resource.h.

typedef enum _WQ_PDM_FREQ_SAMPLE WQ_PDM_FREQ_SAMPLE: For specific definitions, please refer to the header file wq_audio_resource.h.

typedef enum _WQ_PDM_TX_CHANNEL WQ_PDM_TX_CHANNEL: For specific definitions, please refer to the header file wq_audio_resource.h.

typedef struct wq_pdm_gpio_cfg wq_pdm_gpio_cfg_t: For specific definitions, please refer to the header file wq_pdm.h.

typedef struct wq_pdm_cfg wq_pdm_cfg_t: For specific definitions, please refer to the header file wq_pdm.h.

typedef struct wq_pdm_rx_chn_cfg wq_pdm_rx_chn_cfg_t: For specific definitions, please refer to the header file wq_pdm.h.

typedef union wq_pdm_rx_en wq_pdm_rx_en_t: For specific definitions, please refer to the header file wq_pdm.h.

typedef struct wq_pdm_rx_analog_param wq_pdm_rx_analog_param_t: For specific definitions, please refer to the header file wq_pdm.h.

Functions

WQ_RET wq_pdm_rx_init(void)

This function is to initialize pdm rx.

返回:: WQ_RET_OK - success, other - failed

WQ_RET wq_pdm_rx_deinit(void)

This function is to deinitialize pdm rx.

返回:: WQ_RET_OK - success, other - failed

WQ_RET wq_pdm_tx_init(void)

This function is to initialize pdm tx.

返回:: WQ_RET_OK - success, other - failed

WQ_RET wq_pdm_tx_deinit(void)

This function is to deinitialize pdm tx.

返回:: WQ_RET_OK - success, other - failed

WQ_RET wq_rx_pdm_open(WQ_PDM_PORT port, WQ_PDM_RX_CHANNEL chn, const wq_pdm_cfg_t *pdm_cfg)

Open pdm rx and configure the hardware of pdm rx.

参数:

port -- pdm rx port
chn -- pdm rx channel
pdm_cfg -- the configuration of the selected pdm rx

返回:

WQ_RET_OK - success, other - failed

WQ_RET wq_rx_pdm_close(WQ_PDM_PORT port, WQ_PDM_RX_CHANNEL chn, const wq_pdm_gpio_cfg_t *pdm_gpio_cfg)

Close pdm rx and disable corresponding hardware.

参数:

port -- pdm rx port
chn -- pdm rx channel
pdm_gpio_cfg -- gpio configuration corresponding to pdm rx

返回:

WQ_RET_OK - success, other - failed

WQ_RET wq_rx_pdm_micbias_start(const wq_pdm_rx_analog_param_t *param)

Start pdm rx micbias.

参数:: param -- pdm mic and micbias parameter config
返回:: WQ_RET_OK - success, other - failed

WQ_RET wq_rx_pdm_micbias_stop(const wq_pdm_rx_analog_param_t *param)

Stop pdm rx micbias.

参数:: param -- pdm mic and micbias parameter config
返回:: WQ_RET_OK - success, other - failed

WQ_RET wq_rx_pdm_start(WQ_PDM_RX_CHANNEL chn, const wq_pdm_rx_chn_cfg_t *cfg)

Start pdm rx.

参数:

chn -- pdm rx channel
cfg -- pdm rx channels config

返回:

WQ_RET_OK - success, other - failed

WQ_RET wq_rx_pdm_stop(WQ_PDM_RX_CHANNEL chn)

Stop pdm rx.

参数:: chn -- pdm rx channel
返回:: WQ_RET_OK - success, other - failed

void wq_rx_pdm_data_start(WQ_PDM_RX_CHANNEL chn)

Trigger adc data for pdm rx.

参数:: chn -- pdm rx channel

WQ_RET wq_rx_pdm_gain_set(WQ_PDM_RX_CHANNEL chn, int16_t gain)

Set pdm rx gain, the gain pre step is 0.1875dB.

参数:

chn -- : pdm rx channel
gain -- target gain

返回:

WQ_RET_OK - success, other - failed

WQ_RET wq_rx_pdm_sample_rate_set(WQ_PDM_RX_CHANNEL chn, uint32_t out_fs, bool less_delay_mode_en)

Set pdm rx sample rate.

备注

Please call this interface after PDM open, and before RX-FIFO link. If set the sample rate after PDM started, some dirty data should be discarded, it is recommended to discard no less than 10 sample points.

参数:

chn -- pdm rx channel
out_fs -- Output sample rate
less_delay_mode_en -- Less delay mode enable

返回:

WQ_RET_OK - success, other - failed

uint32_t wq_rx_pdm_get_chn_clk(uint8_t chn)

Get the rx dfe clk corresponding to pdm.

参数:: chn -- is pdm rx channel
返回:: uint32_t return clk

WQ_RET wq_tx_pdm_open(const wq_tx_dfe_digtal_config_t *dfe_cfg, const wq_pdm_cfg_t *pdm_cfg)

This function is to open pdm tx and digital part of corresponding tx dfe. and does not work with output as spk.

参数:

dfe_cfg -- is txdfe configuration.
pdm_cfg -- is pdm tx configuration.

返回:

WQ_RET_OK - success, other - failed

WQ_RET wq_tx_pdm_close(WQ_PDM_TX_CHANNEL chn, const wq_pdm_gpio_cfg_t *pdm_gpio_cfg)

This function is to clsoe tx pdm and corresponding tx dfe.

参数:

chn -- is pdm tx channel
pdm_gpio_cfg -- is pdm gpio configuration.

返回:

WQ_RET_OK - success, other - failed

WQ_RET wq_tx_pdm_start(WQ_PDM_TX_CHANNEL chn)

This function is to start pdm tx and corresponding tx dfe.

参数:: chn -- is pdm tx channel
返回:: WQ_RET_OK - success, other - failed

WQ_RET wq_tx_pdm_stop(WQ_PDM_TX_CHANNEL chn)

This function is to stop pdm tx and corresponding tx dfe.

参数:: chn -- is pdm tx channel
返回:: WQ_RET_OK - success, other - failed