pointer to array problem

lgeorge123 · Joined: 05 Dec 2004 Posts: 31

I have a ccs c program to display several bitmaps , it depends on variable size . No matter I wrote the pointer ptr1 assign to several variables using Malab IDE sim to stimulate program NO correct array items comes out , so anyone help me solve this problems ????

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Ttelmah · Guest

Read the manual, and the readme.txt.
Note the comments about _const_ arrays.

By default, pointers, point to the RAM. Const arrays are in the ROM. This is a big difference/consequence of the PIC's Harvard memory architecture.

Now, depending on how 'late' your compiler is, you can construct pointers to ROM, by a number of routes. Each imposes a significant overhead.
1) Declare the arrays as ROM, not const. This tells the compiler to add the extra code to support pointers. Downside, sightly larger, and accesses are slower.
2) Select 'PASS_STRINGS_IN_RAM', or #device CONST=READ_ONLY. This involves a significant RAM overhead, but makes the CONST arrays behave like ANSI (read only), and copies them into RAM as necessary, allowing pointers.
3) Select CONST=ROM. Makes stuff declared as const, behave like it is declared as ROM. Downside is the space/speed, and it'll apply to all const declarations.
Remember also, that your pointers may need to be declared as pointers to constants.

Best Wishes