Arduino - SPIusingInterrupt says
interruptNumber: the associated interrupt number
I was asking
- What is an interruptNumber?
The question is still a interesting to me, but it moot to me now given that the 255 I am using (thinking I was taking the lazy way out) is the way you do it with the timer compare A interrupt and all timer interrupts...
Seems odd that the timers would be all part of a generic case, but that is an easy thing to do once you find the magic 255.
This is from SPI.h:
// If SPI is used from within an interrupt, this function registers // that interrupt with the SPI library, so beginTransaction() can // prevent conflicts. The input interruptNumber is the number used // with attachInterrupt. If SPI is used from a different interrupt // (eg, a timer), interruptNumber should be 255. static void usingInterrupt(uint8_t interruptNumber);