Question about PIC CCS compiler

I need to write a routine that Checksums the program memmory on a PIC
using the CCS compiler.
I want to declare a pointer to program space.
I thought that I could just declare a "const char * ptr" but the
compiler does not seem to like this.

Any one know how to get a pointer to program space?

Thanks,

Bob Weiman

On 15 Mar 2004 08:24:28 -0800, google.4.oracle@xoxy.net (Bob) wrote:

>I need to write a routine that Checksums the program memmory on a PIC
>using the CCS compiler.
>I want to declare a pointer to program space.
>I thought that I could just declare a "const char * ptr" but the
>compiler does not seem to like this.
>
>Any one know how to get a pointer to program space?

The problem is the PIC, not the compiler.  There is no way to access
program memory on 12 and 14 bit PIC cores.  For example, code up
something like

   unsigned char const array[5] = {1, 8, 4, 3, 6};

An see what it compiles to.  Hint: it's a subroutine that returns the
the specified value for the passed index.

Not sure about 16 bit cores.  I think there might be a way with those.

Regards,

                               -=Dave
-- 
Change is inevitable, progress is not.

Dave Hansen wrote:
> 
> On 15 Mar 2004 08:24:28 -0800, google.4.oracle@xoxy.net (Bob) wrote:
> 
> >I need to write a routine that Checksums the program memmory on a PIC
> >using the CCS compiler.

> The problem is the PIC, not the compiler.  There is no way to access
> program memory on 12 and 14 bit PIC cores.  

That must depend on the particular device.  The 16F88, a newer 14-bit
device, extends the EEPROM read/write interface to cover the flash code
space as well.  You can use it to checksum the program.  I doubt you can
use pointer syntax, though, for access.

Thad

google.4.oracle@xoxy.net (Bob) wrote in message news:<aacb3d3a.0403150824.ccc5174@posting.google.com>...
> I need to write a routine that Checksums the program memmory on a PIC
> using the CCS compiler.
> I want to declare a pointer to program space.
> I thought that I could just declare a "const char * ptr" but the
> compiler does not seem to like this.
> 
> Any one know how to get a pointer to program space?
> 
> Thanks,
> 
> Bob Weiman

On the older PICs you can't get to the program space. PICs use a
Harvard architecture, which means program and data spaces are
seperate. Later versions of PICs have a table read instruction that
can be used to read a value from the program space.

You might try looking at the READ_PROGRAM_MEMORY function (also called
READ_EXTERNAL_MEMORY). On PICs that support table read instructions,
these might work.

Happy coding,

Mark

Dave Hansen <iddw@hotmail.com> wrote in message
news:40560d6a.439733828@News.individual.net...
> On 15 Mar 2004 08:24:28 -0800, google.4.oracle@xoxy.net (Bob) wrote:
>
> >I need to write a routine that Checksums the program memmory on a PIC
> >using the CCS compiler.
> >I want to declare a pointer to program space.
> >I thought that I could just declare a "const char * ptr" but the
> >compiler does not seem to like this.
> >
> >Any one know how to get a pointer to program space?

Interesting that the XCSB compiler (structured PIC BASIC) supports pointers
to program memory and a C compiler does not.

>
> The problem is the PIC, not the compiler.  There is no way to access
> program memory on 12 and 14 bit PIC cores

This was correct some time ago but it changed with the 16F87x. These 14 bit
PICs extend the data EEPROM read/write mechanism to cover the program flash.
You can use this mechanism to read any program word. Newer PICs like the
16F818, 16F819 and 16F88 also have this facility.

Regards
Sergio Masci

http://www.xcprod.com/titan/XCSB - optimising structured PIC BASIC compiler

On Tue, 16 Mar 2004 04:46:39 -0000, "Sergio Masci"
<sergio@NO.SPAM.xcprod.com> wrote:

>
>Dave Hansen <iddw@hotmail.com> wrote in message
>news:40560d6a.439733828@News.individual.net...
>> On 15 Mar 2004 08:24:28 -0800, google.4.oracle@xoxy.net (Bob) wrote:
>>
>> >I need to write a routine that Checksums the program memmory on a PIC
>> >using the CCS compiler.
[...]
>> >Any one know how to get a pointer to program space?
>
>Interesting that the XCSB compiler (structured PIC BASIC) supports pointers
>to program memory and a C compiler does not.

And what exactly can you do with such a pointer on a 16C711 or a
12C508?  A ROM checksum?  I don't think so.

CCS does allow you to declare an array of constants or a string to be
stored in program memory, as I posted before.  But it gets implemented
as a subroutine taking the index as a parameter and returning the
value at the index.

Neither C nor Basic is going to be able to support anything that can't
be done in assembly.

>
>>
>> The problem is the PIC, not the compiler.  There is no way to access
>> program memory on 12 and 14 bit PIC cores
>
>This was correct some time ago but it changed with the 16F87x. These 14 bit
>PICs extend the data EEPROM read/write mechanism to cover the program flash.
>You can use this mechanism to read any program word. Newer PICs like the
>16F818, 16F819 and 16F88 also have this facility.

Cool.  Can you re-write program memory as well?  Bootloader kinds of
things?  That would imply that PIC "Flash" is, in fact, EEPROM.  I
haven't had a chance to use these parts yet.

There are, however, a lot more 16Cxx and 12Cxx parts available than
16Fxx or 12Fxx parts.

Regards,

                               -=Dave
-- 
Change is inevitable, progress is not.

Dave Hansen <iddw@hotmail.com> wrote in message
news:40570a42.504471781@News.individual.net...

>
> CCS does allow you to declare an array of constants or a string to be
> stored in program memory, as I posted before.

You do not state this anywhere in your previous post and the OP said
(with explicit reference to the CCS compiler)
        "I thought that I could just declare a "const char * ptr" but the
compiler does not seem to like this"

Given your incorrect general assertion that:
        "There is no way to access program memory on 12 and 14 bit PIC
cores"
I assumed you were talking about C compilers for the PIC in general. My
comment was regarding a specific C compiler that according to the OP did not
seem to support pointers to program memory.

Regards
Sergio Masci

http://www.xcprod.com/titan/XCSB - optimising structured PIC BASIC compiler

I have found the solution using (as Mark Hahn suggested) the
read_program_eeprom() routine. Reading program space is definitely
support on the F876.

Bob