PlayBack

Implement the function of outputting audio by encoding a 1KHz sine wave signal through the CODEC.

Use DMA to transfer I2S data from memory to the Transmit FIFO of I2S, and then encode it into a PDM signal through the CODEC.

By connecting an external PDM player, it can play a fixed frequency sine wave voice.

Requirements

The sample supports the following development kits:

Development Kits

Hardware Platforms

Board Name

RTL87x2G HDK

RTL87x2G EVB

For more requirements, please refer to Quick Start.

Wiring

EVB external recording and playback module, connect P4_3 and CLK, P4_2 and DATA.

Building and Downloading

This sample can be found in the SDK folder:

Project file: samples\peripheral\codec\playback\proj\rtl87x2g\mdk

Project file: samples\peripheral\codec\playback\proj\rtl87x2g\gcc

To build and run the sample, follow the steps listed below:

  1. Open sample project file.

  2. To build the target, follow the steps listed on the Generating App Image in Quick Start.

  3. After a successful compilation, the app bin app_MP_xxx.bin will be generated in the directory mdk\bin or gcc\bin.

  4. To download app bin into EVB board, follow the steps listed on the MP Tool Download in Quick Start.

  5. Press reset button on EVB board and it will start running.

Experimental Verification

You can hear the sound of a 1KHz sine wave in the PDM player.

Code Overview

This chapter will be introduced according to the following several parts:

  1. Source Code Directory.

  2. Peripheral initialization will be introduced in chapter Initialization.

  3. Functional implementation after initialization will be introduced in chapter Functional Implementation.

Source Code Directory

  1. Project Directory: sdk\samples\peripheral\codec\playback\proj

  2. Source Code Directory: sdk\samples\peripheral\codec\playback\src

Source files are currently categorized into several groups as below.

└── Project: playback
    └── secure_only_app
        └── Device                   includes startup code
            ├── startup_rtl.c
            └── system_rtl.c
        ├── CMSIS                    includes CMSIS header files
        ├── CMSE Library             Non-secure callable lib
        ├── Lib                      includes all binary symbol files that user application is built on
            └── rtl87x2g_io.lib
        ├── Peripheral               includes all peripheral drivers and module code used by the application
            ├── rtl_rcc.c
            ├── rtl_pinmux.c
            ├── rtl_gdma.c
            ├── rtl_nvic.c
            ├── rtl_codec.c
            └── rtl_i2s.c
        └── APP                      includes the ble_peripheral user application implementation
            ├── main_ns.c
            └── io_codec.c

Initialization

The initialization process includes the initialization of the CODEC, UART, I2S, and DMA modules as follows.

board_codec_init contains the PAD and PINMUX settings for PDM.

  1. Configure PAD: set pins, PINMUX mode, PowerOn, no internal Pull-Up.

  2. Configure PINMUX: Assign pins to PDM_CLK, PDM_DATA functions respectively.

board_i2s_init contains the PAD and PINMUX settings for I2S.

  1. Configure PAD: set pins, PINMUX mode, PowerOn, no internal Pull-Up.

  2. Configure PINMUX: Assign pins to BCLK_SPORT0, LRC_SPORT0, DACDAT_SPORT0 functions respectively.

driver_i2s_init contains the initialization of I2S peripherals.

  1. Enable PCC clock.

  2. Set the I2S bit clock to 16kHz.

  3. Set master device mode, dual channel output, data format to I2S mode.

  4. Set data width to 24 bits and channel width to 32 bits.

driver_gdma_init contains the initialization of GDMA peripherals.

  1. Enable PCC clock.

  2. Use GDMA channel 0.

  3. GDMA transfer direction is memory to peripheral transfer.

  4. Source address is codec_drv_cos_table and destination address is (&(I2S0->I2S_TX_FIFO_WR_ADDR).

  5. Enable GDMA channel 0 total transfer completion interrupt GDMA_INT_Transfer.

driver_codec_init contains the initialization of CODEC peripherals.

  1. Enable PCC clock.

  2. Initialize the configuration of the CODEC’s analog circuit.

  3. Set the playback mode to un-muted.

  4. Set the playback gain.

  5. Set DAC dither to DISABLE.

  6. Set data format to I2S format.

  7. Set channel length, data width, and channel order.

RCC_PeriphClockCmd(APBPeriph_CODEC, APBPeriph_CODEC_CLOCK, ENABLE);
CODEC_AnalogCircuitInit();
...
CODEC_InitStruct.CODEC_DaMute = CODEC_UNMUTE;
CODEC_InitStruct.CODEC_DaGain = 0xAF;
CODEC_InitStruct.CODEC_DaC_Dither = DAC_DA_DITHER_DISABLE;
CODEC_InitStruct.CODEC_I2SFormat = CODEC_I2S_DataFormat_I2S;
CODEC_InitStruct.CODEC_I2SChannelLen = I2S_CHANNELLEN_32;
CODEC_InitStruct.CODEC_I2STxDataWidth = CODEC_I2S_Tx_DataWidth_24Bits;
CODEC_InitStruct.CODEC_I2SChSequence = CODEC_I2S_CH_L_R;

Functional Implementation

  1. Execute preload_cos_table to prepare the sine wave data to be sent.

  2. Enable I2S transmit mode and receive mode; enable GDMA channel 0.

I2S_Cmd(I2S0, I2S_MODE_TX | I2S_MODE_RX, ENABLE);
GDMA_Cmd(GDMA_Channel_DMIC_NUM, ENABLE);

  1. Use GDMA to carry the sine wave data to the I2S0 transmit FIFO; when the data transfer is complete, trigger the GDMA_INT_Transfer interrupt and enter the interrupt handler function CODEC_GDMA_Channel_Handler.

    1. Reset the source and destination addresses.

    2. Reset the GDMA transfer data size.

    3. Clear the GDMA channel 0 GDMA_INT_Transfer interrupt pending bit and enable GDMA channel 0.

GDMA_SetSourceAddress(CODEC_GDMA_Channel, (uint32_t)codec_drv_cos_table);
GDMA_SetDestinationAddress(CODEC_GDMA_Channel, (uint32_t)(&(I2S0->I2S_TX_FIFO_WR_ADDR)));
GDMA_SetBufferSize(CODEC_GDMA_Channel, CODEC_DRV_COS_TABLE_SAMPLE);
GDMA_ClearINTPendingBit(CODEC_GDMA_Channel_NUM, GDMA_INT_Transfer);
GDMA_Cmd(CODEC_GDMA_Channel_NUM, ENABLE);