I am wondering if with daisy chaining or 4 conductor wiring (shielded) in parallel that a Arduino IDE program revision or update could be multicast to 32 Arduino Unos somehow?
I have been told that using I2C would require writing a bootloader (not easy) & that electrical noise vulnerability would be high risk.
I guess Ethernet would work but that would require 32 Ethernet shields that seem would drive up cost more than necessary ... especially if the update of program is all that is needed.
In the subject title ... I meant to say the mostly unused(?) 2x3 six pin header labeled ISP.
The programming protocols are two-way - the target responds to the programmer. That greatly complicates multicast programming!
it doesnt have to be two way. miso is actually optional. i use a custom program to do up to 20 at a time. however most utilities like avrdude do not recognize this and therefor less useful for programming multiple units. I suspect if you wired miso to just one chip and the rest in parallel it could be tricked into doing that.