@supscientist As a place to start, take a look at how Particle’s SPI Library works and see how you can replace the calls to the Arduino SPI Library with calls to the Particle SPI Library in FLASHIO.cpp. Every function in SPIFlash is built on top of the private functions in FLASHIO.cpp that make calls to the SPI Library - so the majority of your work should be done with this step. You might also have to modify some defines in defines.h.