Bluetooth Controllers historically provide SCO data via PCM/I2S interview. While most Embedded Linux systems have an I2S interface, most desktop systems don't have one.
This project aims to provide a mimimal I2S Interface over a regular UART connection using off-the-shelve hardware, like the STM32L432KC Nucleo dev kit.
| Signal | GPIO | Header | Pin | Arduino | Logic |
|---|---|---|---|---|---|
| GND | CN3 | 4 | GND | Gray | |
| SAI-SCK | PA8 | CN3 | 12 | D9 | Black |
| SAI-FS | PA9 | CN3 | 1 | D1 | Brown |
| SAI_SDO | PA10 | CN3 | 2 | D0 | Red |
| SAI-SDI | PB5 | CN3 | 14 | D11 | Orange |
| VCP_TX | PA2 | CN4 | 5 | A7 | Yello |
| VCP_RX | PA15 | Green |
PA15 (VCP_RX) is only available at SB3 on the bottom of the Nucleo board
- Slave
- Philips I2S
- 16 bit PCM
- 8 bit mSBC
- 230400 baud (sufficient for 1 Channel, 8 kHz, 16 bit = 128 kbps)
- 8N1 (8 Bit data, 1 Stop Bit, No Parity)
The bridge will buffer a fixed amount of data from UART before it starts sending data over I2S. This allows the host to send one block for each received block without additional buffering. If I2S clock stops for 100 ms, the state is reset.
Compile the project using Cmake and flash onto the L432. As I2S is configured as slave, it will only start sending data once the clock starts.
In main.c, you choose choose one of the following I2S output modes either by setting it in the code or via the SEGGER RTT Terminal:
- '1' Forward UART to I2S (default)
- '2' Sine PCM 8 kHz/16 bit, 266 Hz
- '3' Sine PCM 16 kHz/16 bit, 266 Hz
- '4' Sine mSBC 266 Hz
- '5' Silence PCM 8 kHz/16 bit
- '6' Silence mSBC
Similarly, you can choose one of the following modes for the data sent over UART in big-endian format.
- 'a' Forward Left I2S Channel data (default)
- 'b'. Sine PCM 8 kHz/16 bit, 266 Hz
- 'c'. Sine PCM 16 kHz/16 bit, 266 Hz
- 'd'. Sine mSBC 266 Hz
- 'e'. Silence PCM 8 kHz/16 bit
- 'f'. Silence mSBC
- 'g'. Test Data Counter