The provided module spi_master.c has timeout code and error returns from spi_master_tx_rx(...)
Given that there are no external control signals to the SPI block, only a data input, it should be impossible for this hardware to timeout. I checked the current PAN V2.0 and there are no problems listed for the SPI section.
Please explain why there is timeout code.
My research:
In my application, I am not using PPI or interrupts with SPI.
In using the SPI hardware, I do indeed see timeout problems. My research seems to show that the problems are related to faster rather than slower SPI frequency (I see a problem if it is 2 MHz, but not if 250 KHz), and also seems to be related to the double buffer on the TX path.
If I send the first two bytes one immediately after the other (as shown on page 131 Ref Manual V1.1 (matches my silicon rev), or page 138 on Ref Manual V2.1) it times out on EVERY transfer at 2 MHz.
If I only TX another byte after the prior data has been completed, and the received byte read, it does not time out. While this works, it is much slower than what should be possible. My application is an AD7680 ADC, and I need to read 3 bytes, preferably at 2 MHz.
Please explain what is really going on.
