In view of the silence on this subject, I'll just tell you about my (few)
experiences of PIC EEPROM programming. I was using the 16F series, but I would
imagine there are similarities.
Programming the EEPROM on PICs, as I understand it is a runtime thing, rather
than a program time (or compile time) thing. So, suppose that I wanted to
store "1234" as a default lock combination in EEPROM, I would have to have the
"1234" as a constant in the code space and program the EEPROM at the first
actual execution of the code on the PIC chip. I seem to recall that
programming the EEPROM is quirky too - and I think there's even an interrupt
to indicate the write cycle is complete! I seem to recall that I had to write
an assembler fragment to actually perform the write because the timing of the
compiled C code wasn't right.
There are issues which might be relevant to this, particularly if there's a
power interruption during the write cycle leaving you with a corrupt EEPROM. I
think I chose to ignore this scenario after due consideration, but it's
something you need to be aware of.
The code that I wrote was for a different compiler (and I haven't ported it to
SDCC), but if you continue to be stuck I'll try and dig it out for you - you
might glean something from it.
On Friday 15 October 2010 15:03:19 Alan Hourihane wrote:
> On Wed, 2010-10-13 at 16:24 +0100, Alan Hourihane wrote:
> > Hi,
> >
> > I wonder if someone can help.
> >
> > I'm using a PIC18F242 / PIC18F2420 and sdcc 2.9.0 and currently using
> > this code to pop things into EEPROM storage.
> >
> > __code unsigned char __at( 0xf00000 )
> > values[] = {
> > 0x00, 0x01,
> > 0x02, 0x03,
> > 0x04, 0x05,
> > };
> >
> > Unfortunately, when I use the EEPROM read commands for index 0, I get
> > 0x00, for index 1, I get 0x02, and index 2, I get 0x04.
> >
> > I've read articles that say the EEPROM needs to be padded to 16bits for
> > the above PICs, and was hoping that I could declare with __eeprom
> > instead of __code and sdcc would fix this up for me but it seems that
> > __eeprom isn't done for PIC16. I don't want to have to declare as a
> > 'short' as then it impacts the code itself to cater for /2 situations.
> >
> > Any help much appreciated ?
>
> Anyone got any clues ?
>
> Thanks,
>
> Alan.
<snip>
--
Richard.
PGP Key-id: 0x5AB3D350
Heuristics are bug ridden by definition. If they didn't have bugs,
then they'd be algorithms.
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