[fpc-devel] Realtime systems using FPC

Mark Morgan Lloyd markMLl.fpc-devel at telemetry.co.uk
Wed Jul 3 12:36:58 CEST 2013

Michael Schnell wrote:
> On 07/03/2013 10:11 AM, Mark Morgan Lloyd wrote:
>> Do you have any URLs etc. for the BBB in this context? 
> This has close to nothing to do with the BeagleBone board: it's just a 
> processor feature. The BeagleBone board in fact supports it as several 
> pins of the chips that can internally be connected to the peripherals 
> that are in "vicinity" of the M3s "PRUS" (="Programmable Real-Time Unit 
> Subsystem"). In fact all peripherals are accessible by all CPUs and DMA 
> controllers, but there might be performance degradation when traversing 
> bus bridges.

So there's a (slight) risk that a careless kernel on the main CPU could 
mess up something safety-critical, or at least (as you've said) could 
have a small effect on timing.

> To learn more, you might want to read the "AM335x Applications Processor 
> Technical Reference Manual" by TI (4788 pages).

That I'll leave to the colleague who hassles me on this sort of thing :-)

>> Could the realtime stuff realistically be coded in FPC, or would this 
>> effectively mandate a distinct target?
> I don't know if fpc can generate ARM M3 code. This might be possible. 
> You need to ask the compiler experts on that.
> I also don't know (yet) what development support is provided by TI for 
> the PRUS. Of course a gcc is available. I do hope that there is support 
> for GDB either vie JTAG or somehow via the main processor. In fact the 
> PRUS does include Ethernet hardware, so I suppose TI should provide a 
> TCP/IP stack for this purpose. Hopefully they have an Eclipse based IDE 
> to do PRUS development.
> I suppose in most cases you will need to do just very small programs to 
> run on the PRUS and provide the very hard realtime stuff. Thus extremely 
> comfortable development tools are not that critical.

So something like a ladder logic interpreter would be entirely viable, 
even if the guts had to be written in C.

Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]

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