Hi Raphael!

Accesing via generic pointers would be amazing. If you had time, I would love to see it implemeted.
The __eeprom keyword can wait, hehe!

Maybe I could help you with implementation of eeprom reads and writes. I could start with device/lib/pic16/libsdcc/gptr/*.c which I think that I understand, and send the patch to you so you can check if it's ok. I don't know what to do in src/pic16/gen.c, though.

After reading the code in the repository, I think that code memory reads via pointers are implemented but code memory writes are not, right?

Thank you very much.

On Sat, Apr 14, 2012 at 11:59 PM, Raphael Neider <rneider@web.de> wrote:
Hi,

> I had always used a library with the following functions to read/write
> eeprom memory:
>
> uint8_t eeprom_read(uint8_t address);
> void eeprom_write(uint8_t address, uint8_t value);
> uint8_t eeprom_write_and_verify(uint8_t address, uint8_t value);
>
> Reading the SDCC manual again, I started thinking that it may also be done
> using pointers without needing this functions. Can it be done? If yes, how?

It is planned (but obviously not yet implemented) to allow access to
EEPROM via the generic pointer mechanism. EEPROM would be mapped into
the generic address space at 0x40.0000..0x7F.FFFF; 0x00.0000-0x3F.FFFF
is code/program memory, 0x40.0000-0x7F.FFFF is supposed to be EEPROM,
and 0x80.0000-0xFF.FFFF is data memory. Once this feature is
implemented, access to EEPROM is as simple as

uint8_t __at(0x400000) eeprom_start;
uint8_t * const eeprom = &eeprom_start;

uint8_t eeprom_read(uint8_t address) {
 return eeprom[address];
}

void eeprom_write(uint8_t address, uint8_t value) {
 eeprom[address] = value;
}

uint8_t eeprom_write_and_verify(uint8_t address, uint8_t value) {
 volatile uint8_t *ee = (volatile uint8_t *)eeprom;
 ee[value] = value;
 return (ee[value] ^ value); /* or whatever is desired for verification */
}

If desired, I can try to implement this. Basically, adjustments need
to be done in two places: device/lib/pic16/libsdcc/gptr/*.c must
certainly be adjusted to actually implement EEPROM access, and
src/pic16/gen.c must probably be adjusted to generate EEPROM access on
certain pointer dereferences. One might want to introduce/enable some
keyword (__eeprom?) to allocate objects in EEPROM space like
__eeprom uint8_t in_eeprom; /* initialisers will be more difficult */
but that may not be too urgent.

Best regards
Raphael

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