Using a PIC together with an ARM for industrial control?

[Zer0flag]

Hi all!

What do you think of the idea to use an ARM CPU together with a PIC for industrial control.
The ARM CPU would run embedded Linux to control a color TFT display with a nice GUI and a touchscreen, a PC interface (RS232, USB and Ethernet).
The PIC would do the actual industrial control, e.g. A/D and D/A as well as monitoring some IO pins.
Through the separation of the interface/display electronics (done by ARM) form the real control (done by PIC) there would be no need to use an RTOS. The PIC would take care of all the "real time" stuff and just get instructions from the ARM what to do and deliver some data for the ARM to display. IMHO embedded (non real-time) Linux would be enough for that.
Both microcontrollers could communicate through SPI or RS232. Which one would you prefer?
Optocouplers could be used to separate the interface board (with ARM) from the control board (with PIC).

What do you think about my idea?

Regards,
Zer0flag

[SET]

Already did that - we used SPI and RS232, each has it's benefits and issues. RS232 works well receiving bursty data from the PIC due to the ARM's large FIFO, and DMA transfers if required (we used XScale devices). SPI is useful too - ARM acting as master and PIC as slave. In our case optical isolation and DC/DC isolation was used due to the appplication.

[Zer0flag]

Thank you for the info SET. That sounds very encouraging. Can you tell me what kind of OS you used on the ARM side? I looked at the eCos RTOS first which looks very nice. Unfortunately I don't have experience with driver porting/programming and I could not find any single board computer with color TFT / touchscreen interface supported by eCos so far.

Regards,
Zer0flag

[SET]

We looked at eCos as well - in the end, we didnt bother with an OS, as the application was relatively simple (just used Redboot to load the app). The screen work was simply displaying a bitmap graphic and then doing some manipulation of that image.
We are now working on a project using Linux (this one involves a lot more network connectivity, and OS are good for that) - still has a 'co-processor' but this time it's not a PIC (same principle though).

[Zer0flag]

I am afraid I will not manage to make a board work with embedded Linux + TFT + touchscreen - sounds too complicated for me. And all I want is to make the interface "in front of the PIC" just a bit nicer ;)
I see there are boards with e.g. the Intel PXA255 which has onboard LCD controller but looks like these are not supported by eCos :(

[SET]

Microchip do a graphics library (I think its for the PIC24 range) that interfaces to SPI graphic modules - if you want to do simple menus and so on, (no animation!) then thats a simpler route.

Edit - also, checkout ST Cortex based ARMs, they do a graphical library also, again using an SPI display.

[Ken Johnson]

We use QSI Corp color graphic touchscreens with small pics, for a very nice user interface. A bit pricey, but versatile.

Ken

[Zer0flag]

Thank you SET and Ken,

I'm going to check both possibilities.

Zer0flag