Re: [Sdcc-user] pic14: size of array index

[M L <mar...@gm...>]

Hello,
AFAIK it possible  put static (const) arrays like bitmaps in code
memory (values are retrived by retlw instruction internally with sdcc
helpers function), here goes definition of my_data array:

static __code unsigned char my_data[95][7] =
{  {0x95,0x01,0x78,0x67,0x12,0x88,0x11}, {...}};


I inspected .lst  file and whole table is coded correctly in code
memory, starting addres is 0x6f and last address is 0x307:

00006f   3495     retlw 0x95
000070   3401     retlw 0x1
000071   3478     retlw 0x78
000072   3467     retlw 0x67
000073   3412     retlw 0x12
000074   3488     retlw 0x88
000075   3411     retlw 0x11
....

Looks like unsigned char index has problem accesing 37th element of such array,
example:
unsigned char index;
index=36;
my_data[index][0] -> value OK
index= 37;
 my_data[index][0] -> wrong value,

but when I declare:
unsigned int index;

index=36;
my_data[index][0] -> value OK
index= 37;
my_data[index][0] -> value OK,

So wrong values retrieved with char type index may be related to wrong
offset calculation for call to retlw instruction  inside sdcc, like
this:
36*7 = 252
37*7 = 259 -> value beyond 8bit char type, index will be wrapped to 3


regards,
mb

2014-02-12 18:33 GMT+01:00, Gál Zsolt <tra...@fr...>:
> Hello MB,
>
> Could you write more detail about definition of array? As I know, all
> variables takes places in data memory not in code memory. You should give
> modification word for defining variables in code memory. So this is
> littlebit more complicated.
>
> The other point is the size of your array. If its type is char, its size
> will be 95x7 = 665 bytes ( or words if it is takes place in code memory ).
> I think array is bigger those size what a pic14 device can handle.
>
> Zsolt
>
>
> 2014-02-12 17:20 GMT+01:00 M L <mar...@gm...>:
>
>> Hello,
>> I have a 2 dimensional array with static values: unsigned char
>> my_tab[95][7] ={ ..}  and  it's located in a code memory. When I read
>> array with the following code:
>>
>> unigned char index, v;
>>
>> { index is computed  ...}
>>  v=my_tab[index][0];
>>
>>
>> my "v" has unexpected value when computed index is above 36. When I
>> change index to unisgned int, values readings are as expected. Is
>> there any know issues with array index variables in pic14 port?
>>
>> regards,
>> mb
>>
>>
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