[PicForth] multitasker.fs yield seems to generate bad code when multitasker is above 0x1000

[Alex Holden]

My program went over 0x1000 instructions and immediately started 
crashing hard on boot again. It seems to be caused by another 
(different) issue with the code which 'yield' in multitasker.fs 
generates. In my program it's generating an 'andlw 0xca' instruction 
instead of a goto - I couldn't seem to replicate that exactly with a 
minimal example but it is generating 'iorlw 0x18' instead. I'm guessing 
here but I think maybe it's trying to generate 'goto 0x18' and the 
instruction is getting corrupted by an overflow resulting from the 
address being greater than 0xfff. Here's the example code:

$1000 org
include multitasker.fs
task : test1 yield ;
main : test multitasker ;

And the generated code. Note the instruction at address 0x1005 (this 
becomes a goto if you delete the $1000 org above):

0x0000  3010    movlw   0x10
0x0001  008A    movwf   0x0A
0x0002  2807    goto    0x007   ; (init-picforth) (0x1007)
         ; name: test1
         ; max return-stack depth: 0
0x1000  3010    movlw   0x10
0x1001  00A5    movwf   0x25
0x1002  0822    movf    0x22,w
0x1003  008A    movwf   0x0A
0x1004  3006    movlw   0x06
0x1005  3818    iorlw   0x18
0x1006  0008    return
         ; name: (init-picforth)
         ; max return-stack depth: 0
0x1007  303E    movlw   0x3E
0x1008  0084    movwf   0x04
0x1009  302E    movlw   0x2E
0x100A  00A3    movwf   0x23
0x100B  3000    movlw   0x00
0x100C  00A4    movwf   0x24
0x100D  3010    movlw   0x10
0x100E  00A5    movwf   0x25
         ; name: test
         ; max return-stack depth: 0
0x100F  3010    movlw   0x10
0x1010  00A2    movwf   0x22
0x1011  0064    clrwdt
0x1012  0823    movf    0x23,w
0x1013  0084    movwf   0x04
0x1014  0825    movf    0x25,w
0x1015  008A    movwf   0x0A
0x1016  0824    movf    0x24,w
0x1017  0082    movwf   0x02
0x1018  00A4    movwf   0x24
0x1019  0804    movf    0x04,w
0x101A  00A3    movwf   0x23
0x101B  2811    goto    0x011   ;

-- 
------------ Alex Holden - http://www.linuxhacker.org ------------
If it doesn't work, you're not hitting it with a big enough hammer