Post by thread:[PIC] C18 table stuff

On the subject of tables in C18, as I've been tinkering with C (instead of asm) for PICs, I'm going to get into tables soon. Off the top of my head right now, I can see how I'd use TBLPTRU/H/L to point to the correct data, but not sure yet how data is declared and held in memory efficiently, and how these will be 256-byte boundary aligned (though I would think that that's not necessary here). These will be pre-determined values. Anyone care to share an example of how this is done with C18? AFAIK, the mchip app notes all show this in assembly. Cheers, -Neil.

I should also point out that this is for an 18F PIC. Quoting PICdude <spam_OUTpicdude3TakeThisOuTnarwani.org>: {Quote hidden}> On the subject of tables in C18, as I've been tinkering with C > (instead of asm) for PICs, I'm going to get into tables soon. > > Off the top of my head right now, I can see how I'd use TBLPTRU/H/L to > point to the correct data, but not sure yet how data is declared and > held in memory efficiently, and how these will be 256-byte boundary > aligned (though I would think that that's not necessary here). These > will be pre-determined values. > > Anyone care to share an example of how this is done with C18? AFAIK, > the mchip app notes all show this in assembly. > > Cheers, > -Neil. > > >

Put a bit of time into this tonight, and partially answering my own question, I found that I can do it this way (simplified)... // Define data... unsigned char rom LookupTable[10] = { 1,2,3,5,7,9,11,13,17,19 }; // Access/retrieve data... a = LookupTable[5]; But still wondering, is there a more space-efficient way to do this if I directly manipulate TBLPTRU/H/L etc ? Cheers, -Neil. Quoting PICdude <.....picdude3KILLspam@spam@narwani.org>: {Quote hidden}> I should also point out that this is for an 18F PIC. > > > > Quoting PICdude <picdude3KILLspamnarwani.org>: > >> On the subject of tables in C18, as I've been tinkering with C >> (instead of asm) for PICs, I'm going to get into tables soon. >> >> Off the top of my head right now, I can see how I'd use TBLPTRU/H/L to >> point to the correct data, but not sure yet how data is declared and >> held in memory efficiently, and how these will be 256-byte boundary >> aligned (though I would think that that's not necessary here). These >> will be pre-determined values. >> >> Anyone care to share an example of how this is done with C18? AFAIK, >> the mchip app notes all show this in assembly. >> >> Cheers, >> -Neil. >> >> >> -

Hi Neil, I guess you can use these operations (hope someone has better algorithm for you): Initialize table pointer (traditional way): movlw upper ( table ) movwf TBLPTRU movlw high ( table ) movwf TBLPTRH movlw low ( table ) movwf TBLPTRL Initialize table pointer (cheat way, when you are absolutely sure that the table is in the page 0...): clrf TBLPTRU clrf TBLPTRH movlw low ( table ) movwf TBLPTRL Initialize table pointer (cheat way, when you use a separate section in the linker script for the table): clrf TBLPTRU ; assume that the table is on below that range movlw high ( table ) ; load the section address only movwf TBLPTRH clrf TBLPTRL ; table starts at the offset 0 on that section incrementing by one (efficient way) TBLRD*+ ; we do not use the value of TABLAT here so we only incremented the pointer... incrementing manually by one (math operations way, you do not need this...): INCF TBLPTRL CLRF WREG ADDWFC TBLPTRH ADDWFC TBLPTRU incrementing by another number: MOVLW 0x10 ; or other incrementals ADDWF TBLPTRL CLRF WREG ADDWFC TBLPTRH ADDWFC TBLPTRU ; you can leave out this if you absolutely sure it will never overflow incrementing by another number (silly thing, slightly smaller prog mem footprint but much slower): MOVLW 0x10 ; or other incrementals TBLRD*+ DECFSZ WREG,F BRA $-4 Tamas On 17 January 2012 05:28, PICdude <.....picdude3KILLspam.....narwani.org> wrote: {Quote hidden}> Put a bit of time into this tonight, and partially answering my own > question, I found that I can do it this way (simplified)... > > // Define data... > unsigned char rom LookupTable[10] = { 1,2,3,5,7,9,11,13,17,19 }; > // Access/retrieve data... > a = LookupTable[5]; > > But still wondering, is there a more space-efficient way to do this if > I directly manipulate TBLPTRU/H/L etc ? > > Cheers, > -Neil. > > > > > Quoting PICdude <EraseMEpicdude3spam_OUTTakeThisOuTnarwani.org>: > > > I should also point out that this is for an 18F PIC. > > > > > > > > Quoting PICdude <picdude3spam_OUTnarwani.org>: > > > >> On the subject of tables in C18, as I've been tinkering with C > >> (instead of asm) for PICs, I'm going to get into tables soon. > >> > >> Off the top of my head right now, I can see how I'd use TBLPTRU/H/L to > >> point to the correct data, but not sure yet how data is declared and > >> held in memory efficiently, and how these will be 256-byte boundary > >> aligned (though I would think that that's not necessary here). These > >> will be pre-determined values. > >> > >> Anyone care to share an example of how this is done with C18? AFAIK, > >> the mchip app notes all show this in assembly. > >> > >> Cheers, > >> -Neil. > >> > >> > >> --