Emulator (was EFI control)

[Chris Conlon]

At 05:53 PM 2/7/01 -0400, Bill Shaw wrote:

>You've got at least one interested,  but it would need to support the
>'749,  so 128K bits.
>
>1 Flash,  1 static ram, muxes and PIC? I can do the PIC stuff,  I have a
>PICmaster.  It does get more complicated,  but with surface mount it
>can still be reasonably sized.
>
>On startup,  copy the flash to ram and run the ecu out of ram.  When
>changes come in the serial port switch the ecu to flash,  make changes
>to ram,   then switch the ecu back to ram.

This will work well if only a few bytes are changed, so that the changes
can be stored in PIC memory. (After you switch the ECU back to RAM you
have to reapply the same changes to the flash.)

Personally I'd use 2 128k SRAMs, and 128k of whatever nonvolatile you
prefer. This lets you d/l a complete rom image to the PIC's SRAM,
burn it to NV (which may be slowish depending on what you use),
swap the SRAMs (giving the ECU the new image) and then update the PICs
SRAM from NVRAM. You'll need 74xx244s + 74xx245s (or equivalent) so
that either the PIC "bus" or the ECU bus can talk to either SRAM. The
NVRAM, assuming it's flash or parallel eeprom, can also hang off the
PIC bus via 244/245s. This is more HW than you need the other way,
but not a lot more, and it opens up your choice of NVRAM to just
about anything.

Speaking of the PIC "bus", are there PICs available that support an
external data bus with 18+ address lines? If not you'll need to do a
simple fake data bus thing, where you have some output latches for the
addr bus and control bits (/CS, /OE, /WE) and 8 i/o bits for the data
bus. Nothing too tricky. If you want to do the address bits via SPI,
the 'xx595 works very nicely.


   Chris C.

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