[Bulk] Re: [Diy_efi] Modular approach to EFI controllers
Mon Oct 1 09:30:10 UTC 2007
On Mon, 2007-10-01 at 10:49 +0800, Mike wrote:
> Is the FPGA that necessary, I mean, with a fast enough processor
> and the appropriate software it should be a chince, even if you had
> a second CPU doing nothing but the timing and ion sensing etc,
> you are not going to have the spark events coincident so surely
> with a CPU even doing 4Mhz there is enough time, these beasts
> are cheap have good a/d and run 20Mhz etc...
Oh yes. very necessary.
ok, so we overspecc'd it a bit so it can handle (in theory) a W16 engine
configuration with twin spark and twin injector multiport injection, but
the math worked out upwards of 90,000 events per second at redline.
you *could* handle all that on a 20Mz CPU perhaps, but then if theres
one error in that and you lean out at 15,000 RPM or so its bye-bye
engine. much better to have a nice simple state machine do the job
predictably and without bothering the CPU.
if you actually want to _do_ anything with the ion sense data you're
looking at doing thousands of FFTs per second, which starts to really
rack up the amount of CPU grunt you need - and with heavy processing
would come high latency, or the need to design _very_ tight real time
Much easier to have the FPGA do the critical stuff and simply pass data
to the ARM for analysis and receive feedback to modify its controll
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