Subject:
byte data in code space on 16 bit devices
From:
Peter Onion ####@####.####
Date:
10 Aug 2005 22:26:45 +0100
Message-Id: <1123709176.6260.51.camel@HP.RoomLan>
I'm sure I've seen somewhere a gpasm directive that doesn't zero pad
byte data to 16 bits.
I've just fond a problem in sdcc where an array of pointers is assumed
to take 3 bytes per element, but the padding takes it up to 4 bytes so
array access calculations go wrong... I'de like to know how to fix
this before I post the bug report on the sdcc site.
c code :
char * const months[12] = {
"January","February","March","April","May","June",
"July","August","September","October","November","December"
};
Code generated to access the array... Note the "MULLW 0x03" assumes 3
bytes per pointer:
000432 51f9 movf 0xf9, 0, 0x1 MOVF _month, W, B
000434 0d03 mullw 0x3 MULLW 0x03
000436 cff3 movff 0xff3, 0x1 MOVFF PRODL, r0x01
000438 f001
00043a cff4 movff 0xff4, 0x2 MOVFF PRODH, r0x02
00043c f002
00043e 0e04 movlw 0x4 MOVLW LOW(_months)
000440 2601 addwf 0x1, 0x1, 0 ADDWF r0x01, F
000442 0e16 movlw 0x16 MOVLW HIGH(_months)
000444 2202 addwfc 0x2, 0x1, 0 ADDWFC r0x02, F
000446 0e00 movlw 0 MOVLW UPPER(_months)
000448 6a03 clrf 0x3, 0 CLRF r0x03
00044a 2203 addwfc 0x3, 0x1, 0 ADDWFC r0x03, F
00044c c001 movff 0x1, 0xff6 MOVFF r0x01, TBLPTRL
00044e fff6
000450 c002 movff 0x2, 0xff7 MOVFF r0x02, TBLPTRH
000452 fff7
000454 c003 movff 0x3, 0xff8 MOVFF r0x03, TBLPTRU
000456 fff8
array data in the code space.... Note 4 bytes per pointer:
_months:
001604 16ea andwf 0xea, 0x1, 0 DB LOW(_str_16), HIGH(_str_16), UPPER(_str_16)
001606 0000 nop
001608 16f2 andwf 0xf2, 0x1, 0 DB LOW(_str_17), HIGH(_str_17), UPPER(_str_17)
00160a 0000 nop
00160c 16fc andwf 0xfc, 0x1, 0 DB LOW(_str_18), HIGH(_str_18), UPPER(_str_18)
00160e 0000 nop
001610 1702 andwf 0x2, 0x1, 0x1 DB LOW(_str_19), HIGH(_str_19), UPPER(_str_19)
001612 0000 nop
001614 1708 andwf 0x8, 0x1, 0x1 DB LOW(_str_20), HIGH(_str_20), UPPER(_str_20)
001616 0000 nop
001618 170c andwf 0xc, 0x1, 0x1 DB LOW(_str_21), HIGH(_str_21), UPPER(_str_21)
00161a 0000 nop
00161c 1712 andwf 0x12, 0x1, 0x1 DB LOW(_str_22), HIGH(_str_22), UPPER(_str_22)
00161e 0000 nop
001620 1718 andwf 0x18, 0x1, 0x1 DB LOW(_str_23), HIGH(_str_23), UPPER(_str_23)
001622 0000 nop
001624 1720 andwf 0x20, 0x1, 0x1 DB LOW(_str_24), HIGH(_str_24), UPPER(_str_24)
001626 0000 nop
001628 172a andwf 0x2a, 0x1, 0x1 DB LOW(_str_25), HIGH(_str_25), UPPER(_str_25)
00162a 0000 nop
00162c 1732 andwf 0x32, 0x1, 0x1 DB LOW(_str_26), HIGH(_str_26), UPPER(_str_26)
00162e 0000 nop
001630 173c andwf 0x3c, 0x1, 0x1 DB LOW(_str_27), HIGH(_str_27), UPPER(_str_27)
001632 0000 nop
