Serial comms: Point me in the right direction please

[groundFungus]

@jimmer

The sensor boards need to do the following every approx 1ms:
Look for mode change instruction from the main board (single integer).
Do 8 channels of Analog to digital.
Do some calcs.
Send a message (single integer) to the main board.

That is a lot to do in 1ms. Each analogRead takes about 100us. Are the calcs floating point? How long is the message that is sent (number of characters)?

@jimmer

I see that the MOSI/MISO/SCK channels on the TINY24 are the same pins as the ADC channels, does that affect things? ie do I need to use the digital pins instead for my comms.

You can use those pins for either ADC or SPI, not both.

Since the 32u4 has only 1 serial port it is not easy to use serial for comms. You could use I2C or SPI if you have those pins free on the TINYs and the boards are not too far apart.