Re: [avr-gcc-list] How to port "char flash *" used with IAR to avr-gcc?

[Ned Konz]

On Wednesday 20 October 2004 6:43 am, Günter Dannoritzer wrote:

> I have some code that was developed under IAR. Now I want to port it to
> avr-gcc and have some trouble getting a print function to work.
>
> This is the function, used under IAR:
>
>  void PrintStr( char flash *str )
>  {
>      unsigned char count=0;
>
>      while ((str[count] != '\0') && (count != 64)) {
>        UartTransmitByte(str[count++]);
>      }
>  }
>
>
> It prints out the given string to the serial port.
>
> To compile it with avr-gcc I changed function parameter type to:
>
>  void PrintStr( char * str)
>
> leaving the remaining code in the function body the same.
>
> It does not print out any text over the serial port.
>
> I searched for some information of the "flash" type and in the Atmel
> application note #35 it explains that this is a pointer to a flash
> location.
>
> The way I changed that now is, that I made it a pointer to a RAM location.
>
>  From the explanation in the Atmel application note it seems like that
> after reset the whole code gets copied from the flash to the RAM. So if
> I have a PrintStr("Hello World") function call, the "Hello World" string
> should get copied to the RAM as well or am I missing here something?

But why would you want to waste RAM on a constant string?

> Reading through the libc documentation concerning reading data from the
> flash, I guess the other way to do this with avr-gcc would be to use the
> PGM_P and pgm_read_byte function to leave the string in the flash. Would
> that be the equivalent to the IAR flash pointer?
>
> Can anybody give me a hint how to fix this?

Try something like this:

/*
 * compile with:
 *
avr-gcc -O3 -Wall -Wl,-Map,test.map -g -mtiny-stack -mint8 -mmcu=atmega16 -o 
test.elf test3.c
avr-objdump -h -S  test.elf | tee test.lst
*/

#include <avr/pgmspace.h>

void
UartTransmitByte(char c)
{
 /* do something */
}

void
PrintStr(PGM_P str)
{
 PGM_P end = str + 64;
 char c;

 while ((c = pgm_read_byte_near(*str++) != '\0') && str < end)
         UartTransmitByte(c);
}

static const char PROGMEM constantString[] = "this is a constant string in 
ROM\r\n";

void
main(void)
{
 PrintStr(PSTR("this is an unnamed const string\r\n"));
 PrintStr(constantString);
}

-- 
Ned Konz
http://bike-nomad.com