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Pekub
Joined: 20 Dec 2005
Posts: 16
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| Access to ROM const |
 Posted: Wed Nov 23, 2011 10:50 am |
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Hello,
I tried use ROM constant in my program.
Please, can someone explain me what is the right way to access a ROM constant ?
#include <18F26K22.h>
#device CONST=ROM
..
const int8 yy = 10;
int8 xx;
xx = 100;
if(xx < yy) // doesn`t work
;
if(xx < (int8)yy) // it work`s
;
Thank`s
Peter |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Nov 23, 2011 1:25 pm |
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You didn't give a full test program or your compiler version, so I made
a test program and tested it with vs. 4.127. It works. I got this output
in the MPLAB simulator:
| Quote: |
Print this if 100 is NOT less than 10.
|
Test program:
| Code: |
#include <18F26K22.h>
#device CONST=ROM
#fuses XT,NOWDT,PUT,BROWNOUT,NOLVP
#use delay(clock=4M)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//======================================
void main(void)
{
const int8 yy = 10;
int8 xx;
xx = 100;
if(xx < yy) // Is (100 < 10) ?
printf("Print this if 100 is less than 10. \r");
else
printf("Print this if 100 is NOT less than 10. \r");
while(1);
} |
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Pekub
Joined: 20 Dec 2005
Posts: 16
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| Posted: Thu Nov 24, 2011 3:56 am |
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O.K. It`s work.
But try this one:
| Code: |
int8 xx;
const int8 Table[2] = {10, 50};
xx = 100;
if(xx < Table[0])
Led_PrgEE_On();
else
Led_PrgEE_Off();
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Nov 24, 2011 2:13 pm |
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Again, you didn't post your compiler version.
But it works for me. The program below gives this output in MPLAB
simulator. It's correct:
| Code: |
#include <18F26K22.h>
#device CONST=ROM
#fuses XT,NOWDT,PUT,BROWNOUT,NOLVP
#use delay(clock=4M)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//====================================
void main()
{
int8 xx;
const int8 Table[2] = {10, 50};
xx = 100;
if(xx < Table[0])
printf("LED on \r");
else
printf("LED off \r");
while(1);
} |
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Pekub
Joined: 20 Dec 2005
Posts: 16
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| Posted: Sat Nov 26, 2011 4:02 am |
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I tried it maybe 20 times with V 4.127, V 4.122,
but it doesn`t work.
| Code: |
#include <18F26K22.h>
#device CONST=ROM
#fuses INTRC,,NOWDT,PUT,BROWNOUT,NOLVP
#use delay(clock=16000000)
void main()
{
int8 xx;
const int8 Table[2] = {10, 50};
xx = 100;
if(xx < Table[0])
output_high(PIN_B2); // LED On
else
output_low(PIN_B2); // LED Off
while (1)
;
}
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I dont`t understand assembler, but there is a difference between these methods:
.................... if(xx < (int8)Table[0])
00052: CLRF FF8
00054: SETF FF7
00056: MOVLW FE
00058: MOVWF FF6
0005A: CLRF FEA
0005C: MOVLW 06
0005E: MOVWF FE9
00060: CLRF 0B
00062: MOVLW 02
00064: MOVWF 0A
00066: MOVLB 0
00068: BRA 0004
0006A: MOVF 06,W
0006C: SUBWF 05,W
0006E: BC 0076
.................... output_high(PIN_B2);
00070: BCF F93.2
00072: BSF F8A.2
.................... if(xx < Table[0])
00052: CLRF FF8
00054: SETF FF7
00056: MOVLW FE
00058: MOVWF FF6
0005A: CLRF FEA
0005C: MOVLW 06
0005E: MOVWF FE9
00060: CLRF 0B
00062: MOVLW 02
00064: MOVWF 0A
00066: MOVLB 0
00068: BRA 0004
0006A: MOVF 07,F
0006C: BNZ 0074
0006E: MOVF 06,W
00070: SUBWF 05,W
00072: BC 007A
.................... output_high(PIN_B2);
00074: BCF F93.2
00076: BSF F8A.2 |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19350
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| Posted: Sat Nov 26, 2011 5:26 am |
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OK.
What is happening is quite interesting. It appears that if the CONST=ROM device statement is present, it is making the compiler treat the returned value from the table fetch, as a 16bit value, even if it is defined as an 8bit value...
So the extra test, is testing if the the top byte returned is non zero, and if it is, then the value must be larger than an int8 value, so skips the rest of the test....
It doesn't happen if you explicitly type cast, _or_ if you swap the variables. So:
| Code: |
if(Table[0] > xx)
output_high(PIN_B2); // LED On
else
output_low(PIN_B2); // LED Off
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Works fine.
It is a bug, and should be reported, but is very simple to program round.
Best Wishes |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Sat Nov 26, 2011 5:35 am |
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| Quote: | | It is a bug, and should be reported, but is very simple to program round. |
It's present at least for CCS C V4.120 until V4.127. V4.112 is still O.K.
You can cause even more confusion by extending the table to 4 bytes, which makes CCS C treating Table[] as a long quantity.
Once more exceeding all (bad) expectations...
| Code: | const int8 Table[4] = {10, 50, 51, 52};
...
15: if(xx < Table[1])
0090 6AF8 CLRF 0xff8, ACCESS
0092 68F7 SETF 0xff7, ACCESS
0094 0EFD MOVLW 0xfd
0096 6EF6 MOVWF 0xff6, ACCESS
0098 6AEA CLRF 0xfea, ACCESS
009A 0E06 MOVLW 0x6
009C 6EE9 MOVWF 0xfe9, ACCESS
009E 6A0F CLRF 0xf, ACCESS
00A0 0E04 MOVLW 0x4
00A2 6E0E MOVWF 0xe, ACCESS
00A4 0100 MOVLB 0
00A6 D7B8 BRA 0x18
00A8 5209 MOVF 0x9, F, ACCESS
00AA E107 BNZ 0xba
00AC 5208 MOVF 0x8, F, ACCESS
00AE E105 BNZ 0xba
00B0 5207 MOVF 0x7, F, ACCESS
00B2 E103 BNZ 0xba
00B4 5006 MOVF 0x6, W, ACCESS
00B6 5C05 SUBWF 0x5, W, ACCESS
00B8 E206 BC 0xc6
16: printf("LED on \r"); |
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