Board-To-Board abstraction protocol (MUX, eRPC..)

[Davide Dalfra]

Hi Folks

I'm running a design where i have a sort "Expansions" board where all the Analog inputs and RS485 / UARTS port are located.

This board is running a STM32F107 mcu.

Then i have another board running a STM32F429NIH6 MCU, where we handle LCDs, ETH, External Flash & RAM.

The two boards are connected over a SPI-BUS.

The brain of the system is located on the STM32F429, and we can think the F107 is just a "smart" I/O Expansion. I was looking at a sort of abstraction layer which can "simplify" the dialog between the two boards in the more versatile way.

I have some idea in mind, but i'm not sure i'm on the right way:

Before doing all the exchange protocol myself, i would prefer some stable architecture/system.

1. MUX (used in automotive industries). So far i did not find a good implementation online
2. eRPC (https://github.com/EmbeddedRPC/erpc)

Any suggestion from your side?

[Uwe Bonnes]

If the F107 (why such an old part? ) is just a smart IO Expansion, i would connect via serial, I2C, CAN or SPI according to my speed needs.

[Davide Dalfra]

We have stock of that MCU, in this period is like having god sit in front of us.

However connecting it over SPI , CAN, I2C it's quite ok.

My question was more on which protocol can be used over that bus. ISO-TP ported over SPI could be also an idea.

[Uwe Bonnes]

Having stock is always a good thing, especially in these times. Sorry, I did not see "SPI". Filling up all pins of a 216 pin device seems like some bigger effort. Before starting with the F107, reconsider if not some of the pins used on the F7 could be handled by a port extender (slow GPIO, PWM) ,and so get pins free for other task. Having the need for software on both ends (F7 and F1) gives a lot of headaches I would like to not have. If using SPI, connect Chip Select so that commands get an easy visible frame and are independant from each other. I used somethinmg like that to controll an FPGA with many registers from an AVR8.