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Sirio1
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| int32 array length problem |
 Posted: Mon Mar 30, 2009 5:28 am |
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Hello,
I am working witha PIC16F627 and I have to declare a big 1-D int32 array, but I have the error:
*** Error 87 "Main.c" Line 22(21,22): Data item too big
Is there a way to declare a 1-D array of int32 without this problem?
Is there a #pragma or other setting to do in the compiler?
| Code: | const int32 bigarray[120]={
0,
1,
2,
...
...
...
} |
Thanks!
Sirio |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Mon Mar 30, 2009 5:42 am |
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For that array the PIC would have to have 120x4 = 480 bytes of contiguous RAM. PIC RAM is paged and blocks that big are rare. Does your PIC have blocks that big? You may have to split it up into several smaller arrays or get a really big PIC.
_________________
The search for better is endless. Instead simply find very good and get the job done. |
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Ttelmah
Guest
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| Posted: Mon Mar 30, 2009 7:24 am |
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No PIC will have pages that large. To handle this, you would need to be using a 18 chip, which has linear memory addressing, without the page limitations. On the 16 chips, the maximum _possible_ in a page is 128 locations. In fact the chip you are using, only has a _total_ of 224bytes, so trying to fit an array that needs 480bytes, is a 'hiding to nothing'.....
Think small.
Remember you are dealing with a tiny embedded processor. Try to work out ways of avoiding needing so much data.Otherwise you need to switch to larger tools. It is a bit like asking 'Why can't I fit this 40 ton container in my Honda Civic'. Wrong tool for the job. You either need to move the contents in smaller pieces that will fit in the small vehicle, or get a truck....
Best Wishes |
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Guest
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| Posted: Mon Mar 30, 2009 4:03 pm |
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| SherpaDoug wrote: | | For that array the PIC would have to have 120x4 = 480 bytes of contiguous RAM. PIC RAM is paged and blocks that big are rare. Does your PIC have blocks that big? You may have to split it up into several smaller arrays or get a really big PIC. |
Hi SherpaDoug,
Why should I have 480 bytes of RAM contiguous ? why RAM ??? I need to store a table, nothing more, constant, in ROM...
Just a constant lookup table of 120 x 32 bit numbers ...
In ROM I have several Kb of space!
| Ttelmah wrote: |
Remember you are dealing with a tiny embedded processor. Try to work out ways of avoiding needing so much data.Otherwise you need to switch to larger tools. It is a bit like asking 'Why can't I fit this 40 ton container in my Honda Civic'. Wrong tool for the job. You either need to move the contents in smaller pieces that will fit in the small vehicle, or get a truck.... |
It's ok, I know that it's a tiny processor, I'm not asking an MP3 decoder C source for a 12C508  ...
I'm asking the possibility to store a lookup table in ROM of 120 * 4 (32 bits) = 480 bytes of ROM ... Am I asking so much?
I can bring it also with a bicycle, don't understand why should I buy a truck....
What I have discovered is that there is a limitation to array length, not to the room it really use:
if I declare a structure
| Code: | typedef struct myStruct{
int32 Var1;
int32 Var2;
int32 Var3;
int32 Var4;
} Struct32bytes; |
and I declare a
| Code: | | const Struct32bytes VeryBigArray[64]; |
the compiler works ok, or if I declare
| Code: | const int32 bigarray[64]={
0,
1,
2,
...
...
...
} |
the compiler works ok, but if I declare
| Code: | const int32 bigarray[65]={
0,
1,
...
} |
or
| Code: | | const Struct32bytes VeryBigArray[65]; |
the compiler stops and raise an error.
In the first case I have 256 bytes used, but in the second case I have 1024 bytes used ...
This is a stange behavior, isn't it? At the first time, it's an Honda Civic, at the second time it's a truck...
Could it be an identity problem 
Bye!! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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