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Access to program memory

 
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Akutabi



Joined: 18 Aug 2006
Posts: 6

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Access to program memory
PostPosted: Fri Aug 18, 2006 5:08 am     Reply with quote

Hi,

I'm trying CCS compiler and wished to access a char array stored in program memory. To do it, I first tought I could use a pointer but CCS doesn't allow pointers to constant datas.

So I tried to retrieve the address of my first element in the char array to use the function read_program_memory but it didn't work either, so is there a way to access it without using an index to the array ?

Thank you,

Here is the idea I tought could work :

const char msg[] = "Hello World!";
int16 addr;
char *data;

//Retrieve the address in program memory of the first element
addr = &msg[0];

//Read program memory and store it in RAM
do
{
read_program_memory(addr, data, 1);
addr++;
}while(data != NULL);
rwyoung



Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA

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PostPosted: Fri Aug 18, 2006 7:15 am     Reply with quote

Warning: untested, uncompiled! Use at your own risk.

Code:

const char msg[] = "my message";
int8 i;

i = 0;
while(msg[i])
{
   // do something with msg[i]
   i++;
}

If you are going to be using the value of msg[i] then you might want to consider assigning it to a temporary variable rather than allowing the code for the table jump more than once. Execution speed would generally be a bit higher.
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Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Fri Aug 18, 2006 11:14 am     Reply with quote

Look at the asm code generated when accessing a const array. You will see why the read program memory doesn't work.
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