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Role for FPGA or CPLD with Raspberry Pi

michaelkellett

Interesting - we obviously move in rather different circles despite being in the same business:

 

Take the current project:

 

One master processor (ARM Cortex M4 with ARM serial debugging port and 4 wire trace, Ethernet, USB and serial for debugging)

One supervisor processor (ARM Cortext M0 with ARM serial debugging port)

FPGA with JTAG port

Up to 6 slave processors (ARM Cortex M4s with ARM serial debugging ports)

All in one little box about 25cm x 160cm x 5cm

 

Now to bring up the Ethernet on the master processor I can use its serial port for "printf" error messages (from the Ethernet/TCP/IP library) and the ARM debugging port to load/run/trace the processor. The ARM trace interace box (Keil Ulink Pro) is a USB interface to the development PC.

The superivisor processor is connected via another Ulink to another PC.

The FPGA JTAG interface is USB to yet another PC.

The fourth PC runs Wiresharc and is connected by Ethernet to see what's coming out.

 

It would be nice if the debug tools had Ethernet rather than USB interfaces but they don't.

I could isolate the serial debug port but since I must have three other non-isolated connections it's not worth the effort.

 

This system is all quite low power - so certainly safe to humans and fairly safe to computers. (The really exposed parts are the debug interfaces and there is nothing to be done about that since they need fast conenctions to the hardware.)

In the last 10 years I've lost one debugger and one PC due to my mistakes and in the same time at least 10 PCs have just died (as they do) so it's a cost effective approach.

 

Of course when these things connect to external systems handling real power different rules apply.

 

(AFIK most Ethernet interfaces are not specifically tested for mains safety - either during qualification or as part of normal regular safety checks (and the flash test requirement for Ethernet magnetics is 1500V AC which is OK for some equipment but not for all)).

 

Michael Kellett

Parents

  • Hi all,

     

    Thanks for pointing me at this Morgaine.

     

    I think there are a few point to consider here I want to throw in. However I want to be clear that I'm very pro getting schools, collages and Uni's more hands on and involved with things like Raspi and FPGA/CPLDs.

     

    First off from a education point of view we have to consider what you guys are talking about and the target audiance. As someone who has teached kids in electroincs clubs and takes part in school engineering contests (as a judge) I had written this blog on my first views of the Raspi in educations. This was followed up by a head of ICT who poested this on Deaign Spark too.

     

    My point is however that education is just not geared up for the Raspi and certanlly not for FPGAs. I ahve spoken to a teacher only yeasterday about this and she confirmed that they have no idea what they are doing. So throwing FPGAs at them will scary them off. The key point she picked up from my blog above is that unless a package is supplied to schools that is clear and simple to use then it will not get past the teachers desk. This sounds harsh, but its so true. Its take two years for the Arduino to apear in school contests.

     

    Moving on to haveing a CPLD or FPGA attached to a Raspi I think is a good idea. The Raspi is limit in GPIO and anything that can help expand this will be good. As a first off I would use somthing like a simple CPLD as a direct access to the GPIO as this will hold its configuration at power up, allow simple patcheing and basic logic circuits to be run from it.

     

    The XAPP058 is a great starting point for someone to generate a JTAP programmer for the Raspi. This can then use XSVF files to program either the CPLD or another FPGA if attached.

     

    At this basic level I think you could then start offering not only programming but some simple VHDL / Verilog to schools and collages. However as pointed out you can't run the tools on the Raspi so will HAVE to have another machine for this. You then have to ask if this is protical. What is the Raspi really doing in this project that you can't do with a PC or some of the specially designed education kits like ther terasic DE2. Find that answer and argue it and then you can push Raspi and FPGA tech togetter into schools. However in my view, use pre complied XSVF files to teach logic and basic electroincs via the Raspi.

     

    Moving up as I said you can then add larger FPGAs like the Spartan-3, good price point and enough flex for entry levels. However I think what your offering is a high end education kit or a really nice development kit.

     

    Anyway just some of my ideas tio throw in - truned intoa long answer so sorry about that but would be intrested to see anyones developments and hear your views too.

     

    Paul

    (@monpjc)

  • in reply to pjclarke

    I fear that Paul is right about the difficulty of the Pi in schools, and even more so when it comes to stuff like FPGAs. But I do think that their are plenty of people who could help out  - why can't schools get practising engineers in from industry or Unis to help. The schools my kids go to have always been keen to ask for money or fund raising help but never seem to show any desire to tap into parents/supporters brains. If on the back of the Pi wave some kind of support network could be built that we be a good thing. But it would need schools to accept the principle of outsiders doing 'teaching' .

     

    Michael Kellett

  • in reply to michaelkellett

    One thing that would put me off visiting a school would be the requirement to get a 'working with children' card and its equivalents in other countries, and all the drama of insurance and saying approved things. But (never begin a sentence with 'BUT' ), my views seem to be stuck in the 60 and 70's when I was at school.

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