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About storing large amount of data into ROM

 
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About storing large amount of data into ROM
PostPosted: Tue Dec 13, 2005 8:19 am     Reply with quote
hi all,

I think this thread is the continuing version of the one posted not long ago. I was given the ideas of implementation from some kind guys but now having some practical implementation problem.

My problem is, since I am drawing some graphics and building some menus on LCD using 18f8722, there are a huge amount of pre-defined arrays in the code. I used to define all these arrays as constant so as to save RAM but in the end I was running out of ROM.

People recommanded I store these arrays using #ROM separating each array using a separator '~'. At the beginning of the code, a scanning of that storage area is executed to obtain the idea where these arrays are stored in the ROM.

The code is basically like this:

Code:
#include<18f8722.h>
#device *=16
#include<math.h>
#include<stdlib.h>
#include<crc.c>


#USE RS232( BAUD = 9600, XMIT = PIN_G1, RCV = PIN_G2, STREAM = COM_A )

#USE RS232( BAUD = 9600, XMIT = PIN_C6, RCV = PIN_C7, STREAM = COM_B )

#rom 0x18000 = {"abc",'~',"1234",'~'}

int32 startAddress = 0x18000;

void main()
{
   int i;
   int32 j;
   int32 length[2];

   init_devices();

   for(i=0;i<2;i++)
   {
      for(j=0;*(j+startAddress) != '~'; j++)
         ;
      length[i] = j;
      startAddress += (j+1);
   }
         
   fprintf(COM_B,"\nlength 1 = %ld,length 2 = %ld\n",length[0],length[1]);


}


I am storing arrays "abc" and "1234" in program memory, address starting at 0x18000. However, it doesn't work like what I expected. The lengths returned are: 248 and 634 which are obviously wrong. Can people spot any thing weird here?

Also, I was recommanded using #ORG but have no idea how to put this directive in.
ye



Joined: 11 May 2005
Posts: 57
Location: london

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PostPosted: Tue Dec 13, 2005 8:21 am     Reply with quote
sorry I forgot to login....


any thought,plz?
asmallri



Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia

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Re: About storing large amount of data into ROM
PostPosted: Tue Dec 13, 2005 8:52 am     Reply with quote
You are searching for a byte value so you need to tell the compiler to use byte orientated storage in the #rom directive with the int8 specifier. I also added a define so you do not need to statically define the address more than once.

Code:

#define Table 0x18000
#rom int8 Table = {"abc",'~',"1234",'~'}

int32 startAddress = Table;

_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!
ye



Joined: 11 May 2005
Posts: 57
Location: london

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PostPosted: Tue Dec 13, 2005 9:01 am     Reply with quote
Hi Andrew,

Thanks for the reminding.

It still didn't seem to work. the lengths returned changed but still wrong. The returned lengths are now:

length 1 = 248,length 2 = 1068
asmallri



Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia

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PostPosted: Tue Dec 13, 2005 9:30 am     Reply with quote
Code:

#define Table 0x18000
#rom int8 Table = {"abc",'~',"1234",'~'}

int32 startAddress = Table;
byte z;

......

   for(i=0;i<2;i++)
   {
    for (j =0, z=0; z != '~'; j++)         
       read_program_memory(startAddress + j, &z, 1);

    length[i] = j;
    startAddress += (j+1);
    }

_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!
Ttelmah
Guest
PostPosted: Tue Dec 13, 2005 9:31 am     Reply with quote
You can't use pointers to ROM.
To access the ROM memory, use the 'read_program_memory' call, with the address.

Best Wishes
ye



Joined: 11 May 2005
Posts: 57
Location: london

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PostPosted: Tue Dec 13, 2005 10:27 am     Reply with quote
Thanks guys, it works now...

Telmah, you remember you said using #org to avoid memory ovelap. How did you actualy use #org in this case?
Ttelmah
Guest
PostPosted: Tue Dec 13, 2005 1:13 pm     Reply with quote
The current compilers, _should_ create a memory segment if you use #rom. However I have had problems in the past with the compiler putting code into an area defined using this, and feel it is safer to use #org as well.
If you declare for instance:
#org 0x18000,0x180ff
Then the next item, is put into this memory segment. You can use #rom to do this.
So:
Code:

#define Table 0x18000
#org Table, Table+200

#rom int8 Table = {"abc",'~',"1234",'~'}

#org default

Ensures the area is reserved.

Best Wishes
ye



Joined: 11 May 2005
Posts: 57
Location: london

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PostPosted: Wed Dec 14, 2005 4:40 am     Reply with quote
Thanks guys~
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