How does AMC burn flash with engine running?

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GrahamB
MegaSquirt Newbie
Posts: 6
Joined: Wed Oct 20, 2010 12:25 pm

How does AMC burn flash with engine running?

Post by GrahamB »

Hello,
Just a naive question as I try to understand how the microsquirt/MSII code (2.891) works.
I get the basic idea that there are two copies of the structs, one each in flash and ram
(haven't quite figured out how they are placed appropriately, but maybe when I eventually understand memory paging...
:RTFM: :? :RTFM: ... do :RTFM: until(0); )

... but, if the AMC can burn the fuel tables live, why are all there all those large red-print bits in the Megatune manual saying
I must not burn tables with the engine running?
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grippo
Site Admin
Posts: 286
Joined: Mon Feb 16, 2004 6:55 pm

Re: How does AMC burn flash with engine running?

Post by grippo »

When a flash sector is burned, there is no access to flash (where code is). Unfortunately it takes time to erase a flash sector (a few ms as I recall) because it must be done all at once, so nothing can go on and you might experience a miss, less likely if you are at low rpm. Then repogramming back the flash is not a problem. It can be done word by word without stopping the program for any significant period.
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GrahamB
MegaSquirt Newbie
Posts: 6
Joined: Wed Oct 20, 2010 12:25 pm

Re: How does AMC burn flash with engine running?

Post by GrahamB »

Ah! So to be clear, if I'm erasing one sector, I can't read any sector... and this is why the assembler jump to the burn program in ram is necessary?

So typically, a 20ms glitch would be enough to lose synch to a toothed wheel, and an ign_reset will be needed before things can get back to normal,
and hence the outpc.rpm <= 1200 condition on burning.
Ok, thanks. A few more lights have come on :)
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