Multiplexing ICSP to multiple processors...

[richcj10]

Hi,

I am working on a car project and have pic microcontrollers in a few places on the car. On request of the software team, I need to develop a way to multiplex the ICSP to 7-9 processors on the car. Any ideas?

[David_AVD]

How far are the PICs away from each other?

[T3sl4co1l]

Can you not arrange a bootloader or software update function?

Routing ICSP signals across a car is a blatant invitation to awful problems.

Tim

[richcj10]

Some are within inches of each other, some more than 4-5 feet... It depends on the device.
Using a bootloader was my first idea, but making it capable of sending over RS485 the way it is laid out in our system is a lot of work. It would require some smart resetting (soft resetting) and state management...   It was thinking of adding a "hardware cap" to the programing distribution to keep it in a locked out (the actual pins held in a high / low state) state when the car is in normal running mode. You wouldn't program the device while the car was being driven around anyway...

[Jeroen3]

CAN bus bootloader 
Or some addressable bus.

[RABeng224]

Microchip offers a pretty good bootloader, AN1310 I think its called.  I have modified it to run on RS485 and have deployed it on several projects.  We have never had issues with it.  It is written totally in ASM but it is fairly clean so it is easy to follow.  Our micros (PIC18F) have built in EEPROM so we used it to store flags so that a particular micro can be reset into boot mode.  From there, you can use the serial protocol and just add some addressing capabilities.

Good Luck!

[SL4P]

I suspect you could get away with 'sending' ICSP code pretty safely with appropriate buffering and worst case reset/write timing, however the verify pass would require a bit more thinking to be sure each processor is at the party..

Perhaps if this is really necessary without a bootloader, your code could execute a code verification before 'running' - and 'not' blink a LED or whatever to let you know a specific processor is not actively participating.

Why multiple processors running the same code in close proximity in a dirty, high-rel environment?
Other than a very specific application, I can see many ways this might go wrong.

Let us know what you come up with!