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Joined: 17 May 2005
Posts: 213
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| Constant Data Table in ROM- 2 Dimensions? |
 Posted: Tue Dec 27, 2005 6:54 am |
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Hi
I would like to place a 2d array into ROM. It is a constant array, can someone please tell me how to do this?
(When I define it as int P[10][7] some of the data gets mixed up, and I do not know why).
Thank you in advance
a. |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Tue Dec 27, 2005 8:23 am |
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| arrow wrote: | | I would like to place a 2d array into ROM. It is a constant array, can someone please tell me how to do this? |
Have a look at this thread |
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MikeValencia
Joined: 04 Aug 2004
Posts: 238
Location: Chicago
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| Posted: Tue Dec 27, 2005 8:52 am |
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I tried compiling this:
| Code: |
#include <18F458.h>
#fuses HS,WDT128,PROTECT,NOLVP,PUT
#case
int const table[4][3] = {{1,2,3}, {4,5,6}, {7,8,9}, {0xa, 0xb, 0xc}};
void main(void)
{
int x;
x = 10;
}
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And it does compile. I tried printing out the .hex file and disassembly listing, but i couldn't find any pattern of "1,2,3,4,5,6" anywhere in it, so i guess it is stored in some cryptic way. If you have hyperterminal hooked up to a unit, why don't you try printf'ing "table[2, 2]" and it should be giving you the value '9' (i think). |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Dec 27, 2005 11:45 am |
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| Quote: | | I tried printing out the .hex file and disassembly listing, but i couldn't find any pattern of "1,2,3,4,5,6" anywhere in it. |
The compiler will only put the const array into ROM if you put in
a line of C code to access the array. Even then, if you access the
array with constant indexes (such as table[0][0]), the compiler
will optimize that fetch into a MOVLW statement and it won't put the
entire array into ROM. If you want to see the entire array put
into ROM, you must use a variable for at least one of the indexes.
Then edit the .H file for your PIC, and comment out the #nolist
statement at the top. Re-compile and look at the .LST file.
Example:
| Code: | #include <18F452.h>
#fuses XT,NOWDT,NOPROTECT,PUT,BROWNOUT,NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
int const table[4][3] = {{1,2,3}, {4,5,6}, {7,8,9}, {0xa, 0xb, 0xc}};
//=============================
void main()
{
int8 x;
int8 i;
x = table[i][0]; // Use a variable for one of the indexes
while(1);
}
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Here is the top part of the .LST file for the program above.
| Code: | 0000: GOTO 0020
.... #include <18F452.h>
.... /// Standard Header file for the PIC18F452 device ////
.... #device PIC18F452
0004: CLRF FF7
0006: ADDLW 14
0008: MOVWF FF6
000A: MOVLW 00
000C: ADDWFC FF7,F
000E: TBLRD*+
0010: MOVF FF5,W
0012: RETURN 0
0014: DATA 01,02 // Here is the array data.
0016: DATA 03,04
0018: DATA 05,06
001A: DATA 07,08
001C: DATA 09,0A
001E: DATA 0B,0C
.................... //#nolist |
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