I2S Audio out on XIAO NRF52840 Sense distorted

[msfujino]

If you use mbed for BSP, the SPI clock is only 8MHz even if you set SD.begin(SD_CS, 32000000).
Please also refer to the following link.

XIAO_nRF52840 mbed's SPI performance is only 1/3.5 of non-mbed's

I knew that there were differences between “mbed” and “non-mbed” in terms of maximum SPI clock frequency (mbed:8MHz non-mbed:32MHz) and port drive mode (mbed:standard drive non-mded:high drive). However, when I used an OLED display at the same 8 MHz, I found that there was a big difference in frame rate. I investigated and found that the main reason is that the 1-byte transfer time is 5.6uS for “non-mbed” and 19.5uS for “mbed”. The data transfer throughput is only 1/3.5. Be careful when using S…