Tx Polling

This sample application note describes how to use I2S to implement TX data.

With an external logic analyzer, it can see the waveforms of the sent data.

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

Connect P3_2, P3_3, and P4_0 on the EVB to the logic analyzer. P3_2 is LRCK, P3_3 is BCLK, and P4_0 is DATA.

Building and Downloading

This sample can be found in the SDK folder:

Keil

Project file: samples\peripheral\i2s\tx_polling\proj\rtl87x2g\mdk

GCC

Project file: samples\peripheral\i2s\tx_polling\proj\rtl87x2g\gcc

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

Open sample project file.
To build the target, follow the steps listed on the Generating App Image in Quick Start.
After a successful compilation, the app bin app_MP_xxx.bin will be generated in the directory mdk\bin or gcc\bin.
To download app bin into EVB board, follow the steps listed on the MP Tool Download in Quick Start.
Press reset button on EVB board and it will start running.

Experimental Verification

Preparation Phase

Connect P3_2, P3_3, and P4_0 on the EVB to the logic analyzer.

Testing Phase

Observe the i2s output waveform in the logic analyzer.

Here should be a picture of the I2S waveform — i2s output waveform

Code Overview

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

Source Code Directory.
Peripheral initialization will be introduced in chapter Initialization.
Functional implementation after initialization will be introduced in chapter Functional Implementation.

Source Code Directory

Project Directory: sdk\samples\peripheral\i2s\tx_polling\proj
Source Code Directory: sdk\samples\peripheral\i2s\tx_polling\src

Source files are currently categorized into several groups as below.

└── Project: tx_polling
    └── 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_i2s.c
        └── APP                      includes the ble_peripheral user application implementation
            ├── main_ns.c
            └── io_i2s.c

Initialization

The initialization process includes board_i2s_init and driver_i2s_init.

board_i2s_init contains the PAD and PINMUX settings.

Config PAD: Set pin as PINMUX mode, PowerOn, internal Pull-None.
Config PINMUX: Assign pins for BCLK_SPORT0, LRC_SPORT0, DACDAT_SPORT0 functions respectively.

driver_i2s_init contains the initialization of i2s peripherals.

Enable PCC clock.
Set the I2S clock source.
Set I2S_TxBClockMi and I2S_TxBClockNi to determine the BCLK and LRCK frequencies.
Set I2S_DeviceMode to master device mode.
Set I2S_TxChannelType to stereo channel mode.
Set the data width and data format.
Enable I2S TX mode.

Note

BCLK=I2S_ClockSource*(I2S_BClockNi/I2S_BClockMi)=1024K，LRCK=BCLK/64=16K

RCC_PeriphClockCmd(APB_I2S, APB_I2S_CLOCK, ENABLE);
...
I2S_InitStruct.I2S_ClockSource      = I2S_CLK_40M;
I2S_InitStruct.I2S_TxBClockMi         = 0x271;    /* <!LRCK = 16K */
I2S_InitStruct.I2S_TxBClockNi         = 0x10;     /* <!BCLK = 1024K */
I2S_InitStruct.I2S_DeviceMode         = I2S_DeviceMode_Master;
I2S_InitStruct.I2S_TxChannelType      = I2S_Channel_stereo;
I2S_InitStruct.I2S_TxDataWidth        = I2S_Width_16Bits;
I2S_InitStruct.I2S_TxDataFormat       = I2S_Mode;
I2S_Init(I2S_NUM, &I2S_InitStruct);
I2S_Cmd(I2S_NUM, I2S_MODE_TX, ENABLE);

Functional Implementation

Define the data to be sent, execute I2S_SendData() send the data cyclically.

void i2s_senddata(void)
{
    uint32_t i = 0x12348800;

    while (1)
    {
        if (I2S_GetTxFIFOFreeLen(I2S_NUM))
        {
            /* 16bit format, lower half word send first! */
            I2S_SendData(I2S_NUM, i++);
        }
    }
}