Question about SAI data format when using i2s 24bit 16ksps

Younjun · ‎2022-04-28

Hi,

I'm implementing SAI(I2S format) audio project using STM32H7B3-discovery.

I checked data input and output of CS42L51.

Input wave : 100Hz 10mVpp square wave(to CN6 Left pin)
output wave (from CN5 Left pin)

The SAI frame size is 64bit and slot size is 32bit.

SAI and CS42L51 work properly.

But, when i convert input data to integer value, the result was not square wave.

I sent data to desktop using uart. Below picture is result.

First question.

I think the dma and SAI buffer work as below.

Is it right?

Second question.

I sent 32bit 16k sample to desktop using uart.

64bit(left 4byte, right 4byte) x 16,000 = 1,024,000bps = 1.024Mbps

I set uart baud rate to 1.5Mbps.

desktop os is windows 10 and i implemeted serial program using pyserial.

Is this baud rate enough?

Last question.

I convert 24bit data using below code.

def byte3_to_integer(value1, value2, value3):
    d1 = value1 & 0x7F
    d2 = value2 & 0xFF
    d3 = value3 & 0xFF
 
    result = (d1 << 16) + (d2 << 8) + d3
    if (value1 & 0x80) == 0x80:
        result -= 0x800000
 
    return result

Is there anything wrong in the process of converting sample?

This is my previous question(link)

Regards,

Youngjun