Array of more the 256 bytes not accessed properly by index v

[markleman]

<font face="Courier New" size=-1>I have an array of 512 constant bytes, accessing this using a variable as the index fails for index values of >255. Works if the index is constant but then that’s probably the compiler optimising the look up out. Compiler = PCM Version 3.105

Any thoughts?

Mark Leman

#include<16c711.h>
#device *=16 // use 16 bit pointers

const unsigned int8 ConvertTable[]=
{
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x02, 0x02, 0x02, 0x03, 0x03, // 00-0F
....480 more values....
0xFC, 0xFC, 0xFC, 0xFD, 0xFD, 0xFD, 0xFE, 0xFE, 0xFE, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF //1f0-1FF
};

main()
{
long i = 0xaabb; // fill with random value
int c = 0xcc; // fill with random value

c= ConvertTable[0x0080]; //works
i=0x0080;
c = ConvertTable[i]; //works

c= ConvertTable[0x00ff]; //works
i= 0x00ff; // test 8 bit index limit, works
c = ConvertTable[i];

c= ConvertTable[0x0100]; //works
i = 0x0100; //fails - fetches value at index 0x0000
c = ConvertTable[i];


c= ConvertTable[0x1aa]; //works
i = 0x01aa;
c = ConvertTable[i]; // fails - fetches value at index 0x00aa

while (1)
{
output_high(PIN_B0);
output_low(PIN_B0);
}
}</font>
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This message was ported from CCS's old forum
Original Post ID: 13576

[markleman]

Having spoken to CCS support, the CCS C compiler is unable to use constant tables bigger than 256 bytes with the PIC16xx family.

I solved my problem by splitting the 512 byte table in to two halves and selecting a byte from one or other using an IF statement on the high index byte. For larger tables a switch on the high index byte could be used.

Pity the compiler (PCM C Compiler, Version 3.105) did not produce an error message (only faulty code) and the only mention of this restriction in the manual is on P.167 :

"Subscript out of range. A subscript to a RAM array must be at least 1 and not more than 128 elements. Note that large arrays might not fit in a bank. ROM arrays may not occupy more than 256 locations."

Still problem solved and answer shared....

Mark Leman
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This message was ported from CCS's old forum
Original Post ID: 13580

[Mother]

Maybe this is re-visiting stuff you've tried, but what happens with something like this?

i = 0x00ff;
i += 1;
c = ConvertTable[i];

This should prove whether its the assignment or the indexing arithmetic that's the problem.
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This message was ported from CCS's old forum
Original Post ID: 13581

[Yashu]

:=Having spoken to CCS support, the CCS C compiler is unable to use constant tables bigger than 256 bytes with the PIC16xx family.
:=
:=I solved my problem by splitting the 512 byte table in to two halves and selecting a byte from one or other using an IF statement on the high index byte. For larger tables a switch on the high index byte could be used.
:=
:=Pity the compiler (PCM C Compiler, Version 3.105) did not produce an error message (only faulty code) and the only mention of this restriction in the manual is on P.167 :
:=
:="Subscript out of range. A subscript to a RAM array must be at least 1 and not more than 128 elements. Note that large arrays might not fit in a bank. ROM arrays may not occupy more than 256 locations."
:=
:=Still problem solved and answer shared....
:=
:=Mark Leman
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This message was ported from CCS's old forum
Original Post ID: 13625

[Thomas Blake]

Well, it helped me anyhow ... I was under the impression that both RAM and ROM were limited to 128 ....

:=
:="Subscript out of range. A subscript to a RAM array must be at least 1 and not more than 128 elements. Note that large arrays might not fit in a bank. ROM arrays may not occupy more than 256 locations."
___________________________
This message was ported from CCS's old forum
Original Post ID: 13694