Am 03.03.20 um 22:27 schrieb Basil Hussain: > Hi all, > >> Ideally, there would be some kind of fmemcpy function that dealt with >> 'far' pointers. This is what the docs for ST's SPL instructs Raisonance >> users to use, but I don't think any such thing exists in SDCC's standard >> C library. Would it be possible to write an equivalent in assembly? > > Further to this, having now done some experimentation, it appears to me > that with the current state of SDCC it is not actually possible to write > plain C code that will read from or write to flash memory past 32KB, due > to the limitation of memory pointers being 16-bit even in large memory > model mode. > > Using an STM8S208RB, which has 128KB of flash, I attempted writing to > the last block of flash, at address 0x27F7F. It didn't work, and just > hung the processor. I presume this was because the pointer to this > address got truncated to 0x7F7F, which is not within the flash memory > range, and is actually a reserved area (with the SWIM and debug > registers following). > > Would it be possible for SDCC to add 'far' pointers? Then, when using > large memory model, one could choose between conventional 'near' 16-bit > pointers and 'far' 24-bit pointers as and when the code dictates. >
We have an open feature request: https://sourceforge.net/p/sdcc/feature-requests/560/ > I will have to see if I can put together some inline assembly code to > deal with reading and writing from memory locations that need a 24-bit > address, because at present it doesn't seem to be possible with just C > code. Does anyone have any suggestions for that? The easiest is probably to use ldf. It can only read a byte at a time, so it is somewhat slow, and it needs the pointer at a fixed location in memory (i.e. like a static or global variable) so it makes your function non-reentrant. Philipp
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