Implementing FIFO using XIAO BLE Sense

[msfujino]

I recommend connecting an IMU to XIAO_BLE via SPI.
The SPI transfer rate is 19.5 uS/byte for mbed or 5.6 uS/byte for non-mbed, based on the actual measurements in the link below.
When reading 12 bytes (6 data) from the FIFO, I think the FIFO can be sampled at 4.2 kHz or 14.8 kHz.

What is WCS?

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…