Digital Microphone

This example code collects DMIC data and encodes it into PCM voice data using the CODEC.

DMIC collects analog voice data, which is encoded by CODEC and sent to the I2S receive FIFO. The data is then transferred to UART using GDMA.

On the PC side, a serial assistant receives the data transmitted by UART. Audio parsing software is used to analyze the data and play the recorded voice. In this example, the audio parsing software used is Audacity.

Requirements

For requirements, please refer to the Requirements.

In addition, you need to install PuTTY or UartAssist serial assistant tools and audio parsing tools like Audacity on the PC terminal.

Wiring

Connect the DMIC module to the EVB, connecting P2_2 to CLK and P2_3 to DATA.

Connect the FT232 module to the EVB to receive UART data, connecting P3_2 to RXD, and P3_3 to TXD.

Building and Downloading

For building and downloading, please refer to the Building and Downloading.

Experimental Verification

Preparation Stage

Start the PC terminal with PuTTY or UartAssist, use ASCII to receive data, open the UART COM port, and make the following UART settings:

Baud rate: 3000000

8 data bits

1 stop bit

No parity

No hardware flow control

Set the output data bytes to redirect to a file.

Start the audio parsing software and select the parsing format according to the settings in CODEC. In this example, you can refer to the following Audacity settings.

Encoding: 16-bit PCM

Endianness: Little Endian

Channels: 1 channel

Sample rate: 1600 Hz

Testing Stage

From start to finish of recording, the collected voice data is encoded by Codec as PCM data and sent to the PC terminal via UART.
Use the audio parsing software to view the decoded voice waveform and play the voice.

Code Overview

This section introduces the code and process description for initialization and corresponding function implementation in the sample.

Initialization

The initialization flow for peripherals can refer to Initialization Flow in General Introduction.

The initialization process includes initializing the CODEC / UART / I2S / GDMA modules as follows.

Call Pad_Config() and Pinmux_Config() to configure the PAD and PINMUX of the corresponding pins. The I2S pin multiplexing functions are BCLK_SPORT0, LRC_RX_SPORT0, SDI_CODEC_SLAVE, and SDO_CODEC_SLAVE.

void board_codec_init(void)
{
    Pad_Config(DMIC_MSBC_CLK_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_DISABLE,PAD_OUT_LOW);
    Pad_Config(DMIC_MSBC_DAT_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_DISABLE,PAD_OUT_LOW);
    Pinmux_Config(DMIC_MSBC_CLK_PIN, DMIC1_CLK);
    Pinmux_Config(DMIC_MSBC_DAT_PIN, DMIC1_DAT);

    Pad_Config(CODEC_BCLK_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_ENABLE,PAD_OUT_LOW);
    Pad_Config(CODEC_LRCLK_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_ENABLE, PAD_OUT_LOW);
    Pad_Config(CODEC_TX_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_ENABLE, PAD_OUT_LOW);
    Pad_Config(CODEC_RX_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_ENABLE, PAD_OUT_LOW);

    Pinmux_Config(CODEC_BCLK_PIN, BCLK_SPORT0);
    Pinmux_Config(CODEC_LRCLK_PIN, LRC_RX_SPORT0);
    Pinmux_Config(CODEC_TX_PIN,    SDI_CODEC_SLAVE);
    Pinmux_Config(CODEC_RX_PIN,    SDO_CODEC_SLAVE);
}

For the initialization configuration of UART, I2S, and GDMA peripherals, refer to the amic initialize.
Initialize the CODEC peripheral.
1. Call RCC_PeriphClockCmd() to enable the CODEC clock.
2. Execute CODEC_StructInit() and CODEC_Init() to initialize the CODEC peripheral. The configuration parameters for the CODEC initialization are as follows:

CODEC Initialization Parameters
CODEC Hardware Parameters	Setting in the `CODEC_InitStruct`	CODEC
Mic Type	`CODEC_InitTypeDef::CODEC_Ch0MicType`	`CODEC_CH_DMIC`
DMIC Clock	`CODEC_InitTypeDef::CODEC_DmicClock`	`DMIC_Clock_2500KHz`
SampleRate	`CODEC_InitTypeDef::CODEC_SampleRate0`	`SAMPLE_RATE_16KHz`
DMIC Data Latch	`CODEC_InitTypeDef::CODEC_Ch0DmicDataLatch`	`DMIC_Ch_Rising_Latch`
I2S Data Format	`CODEC_InitTypeDef::CODEC_I2SFormat`	`CODEC_I2S_DataFormat_I2S`
I2S Channel Len	`CODEC_InitTypeDef::CODEC_I2SChannelLen`	`I2S_CHANNELLEN_32`
I2S Data Width	`CODEC_InitTypeDef::CODEC_I2SRxDataWidth`	`CODEC_I2S_Rx_DataWidth_16Bits`
I2S Channel Sequence	`CODEC_InitTypeDef::CODEC_I2SChSequence`	`CODEC_I2S_CH_L_R`

Call I2S_Cmd() to enable the I2S receive mode. Call GDMA_Cmd() to enable GDMA transfer.

Functional Implementation

After DMIC collects the voice data, the CODEC module AD conversion puts the voice data into the I2S RX FIFO. The data in the I2S RX FIFO is then transferred to the UART TX FIFO via GDMA. In the serial assistant, save the data sent by UART to a file, and parse the file data using audio parsing software. The data transmission order in each module is shown in the figure below.

this should be DMIC waveform — Data Transfer Module (DMIC)

When the GDMA transfer amount reaches the set BlockSize, it triggers the GDMA_INT_Transfer interrupt. As the audio data undergoes AD conversion via CODEC, the data size is relatively large and a single GDMA transfer cannot meet the demand. The source address, destination address, and BlockSize are reset in the interrupt handler, and GDMA transfer is re-enabled to ensure the transmission of a large amount of data continuously.
```
GDMA_SetSourceAddress(GDMA_Channel_DMIC, (uint32_t)(&(I2S0->I2S_RX_FIFO_RD_ADDR)));
GDMA_SetDestinationAddress(GDMA_Channel_DMIC, (uint32_t)(&(UART5->UART_RBR_THR)));

GDMA_SetBufferSize(GDMA_Channel_DMIC, AUDIO_FRAME_SIZE / 4);

GDMA_ClearINTPendingBit(GDMA_Channel_DMIC_NUM, GDMA_INT_Transfer);
GDMA_Cmd(GDMA_Channel_DMIC_NUM, ENABLE);
```