Pic16 Boostc Far Array Indexing Error

[Albert 0]

Hi,

 

I found that the index of a far array is only calculated with an 8-bit addition without considering the overflow.

You will find a code example and the resulting assembler file in the attachment.

I think this is an error, at least in the documentation this is not mentioned.

 

Best regards,

 

PS attaching a .asm or .casm don't work, so you will find it below:

 

#include "PIC16F1847.h"

unsigned char uc_arr[192] @0x2270;

void main(void)

{

unsigned char cnt;

for(cnt = 0; cnt < 192; cnt++) {

0004 0020 MOVLB 0x00

0005 01A0 CLRF main_1_cnt

0006 label1

0006 30C0 MOVLW 0xC0

0007 0220 SUBWF main_1_cnt, W

0008 1803 BTFSC STATUS,C

0012 0AA0 INCF main_1_cnt, F

0013 2806 GOTO label1

uc_arr[cnt] = cnt;

000A 3022 MOVLW HIGH(gbl_uc_arr)

000B 0085 MOVWF FSR0H

000C 3070 MOVLW LOW(gbl_uc_arr+D'0')

000D 0084 MOVWF FSR0L

000E 0820 MOVF main_1_cnt, W

000F 0784 ADDWF FSR0L, F

0010 0820 MOVF main_1_cnt, W

0011 0080 MOVWF INDF0

}

}

0009 0008 RETURN

////////////////////////////////////////

// Code with no source :-)

////////////////////////////////////////

0000 2814 GOTO _startup

0014 _startup

0014 3180 MOVLP 0x00

0015 2804 GOTO main

 

TestFarArray.c

[JorgeF 0]

Hi

 

you can use a pointer as a workaround, it generates correct code.

 

 

#include <system.h>
 
unsigned char uc_arr[192]@0x2270;
 
void main(void)
{
    unsigned char cnt;
    unsigned char *ptr = uc_arr;
 
    for(cnt = 0; cnt < 192; cnt++)
    {
        *ptr++ = cnt;
    }
}

generated code

(lines reordered in program flash address order)

 

////////////////////////////////////////
// Code with no source :-)
////////////////////////////////////////
0000  2819   GOTO _startup
  
                             for(cnt = 0; cnt < 192; cnt++) {
0009  01A0   CLRF main_1_cnt
 
000A        label1
000A  30C0   MOVLW 0xC0
000B  0220   SUBWF main_1_cnt, W
000C  1803   BTFSC STATUS,C
000D  0008   RETURN
 
                             *ptr++ = cnt;
000E  0822   MOVF main_1_ptr+D'1', W
000F  0085   MOVWF FSR0H
0010  0821   MOVF main_1_ptr, W
0011  0084   MOVWF FSR0L
0012  0AA1   INCF main_1_ptr, F
0013  1903   BTFSC STATUS,Z
0014  0AA2   INCF main_1_ptr+D'1', F
0015  0820   MOVF main_1_cnt, W
0016  0080   MOVWF INDF0
 
0017  0AA0   INCF main_1_cnt, F
0018  280A   GOTO label1
 
                             }
                    }
 
0019        _startup
0019  3180   MOVLP 0x00
001A  2804   GOTO main

[JorgeF 0]

Hi

 

The problem must be related to the index size (-idx) of the compiler and linker command lines.

But the option for an index size of 2 bytes is only available on the PIC18 compiler (large memory model).

Looks like this RAM access improvement on the PIC16F1xxx family as created a problem for the PIC16 compilers.

 

The pointer workaround works because the maths are done on the pointer variable and not on the indexing SFRs.

 

 

Just my 2 cents on guessing...

 

Best regards

Jorge