I am answering my own question, with an answer. I managed to strip all the unnecessary parts from SPI.h and fit into a very basic uSpi class that I can run in RTC_IRAM_ATTR. This class directly access the SPI3 bus without any manual GPIO. Can be used in wakeup stub, and as far as I tested works grea...

Hi, I am looking for help on a very niche topic, use the SPI in deep_sleep_wake_stub. I have a low power application, where I want to access a display via SPI and send a quick "2 Byte" transfer, then go back to sleep. If I can do this from the deep_sleep_wake_stub, then I measured a save of 33% of p...