[OpenBIOS] PATCH: Implement Forth source debugger for OpenBIOS

Mark Cave-Ayland mark.cave-ayland at siriusit.co.uk
Wed Nov 4 09:53:46 CET 2009

Laurent Vivier wrote:

>> In the meantime, I've looked again at the v2 patch I posted and I still 
>> can't work out why the debugging output by printk() doesn't appear on a 
>> VNC display for Qemu SPARC64, while it appears fine when Qemu SPARC64 is 
>> invoked in -nographic mode. Can anyone shed any light on this?
> Because "printk()" are sent to serial and must use only for debug purpose.
> You must use forth words like "emit" or "type" to send characters to display. For instance, look at "modules/cmdline.c":
> static void
> emit( int ch )
> {
>         PUSH( ch );
>         fword("emit");
> }
> static int
> emit_str( const char *str )
> {
>         int n = 0;
>         while( *str ) {
>                 n++;
>                 emit( *str++ );
>         }
>         return n;
> }

Yeah, I did consider that this might be the case but it still doesn't 
seem to make sense looking at the code. The source for the forth emit 
word can be found in kernel/forth.c:

  *   emit       ( char --  )

static void emit(void)
         cell tmp = POP();
         (void) POP();

while for SPARC64 the source for printk() can be found in 

/* Format a string and print it on the screen, just like the libc
  * function printf.
int printk( const char *fmt, ... )
         char *p, buf[512];
         va_list args;
         int i;

         va_start(args, fmt);
         i = vsnprintf(buf, sizeof(buf), fmt, args);

         for( p=buf; *p; p++ )
         return i;

Both of these use putchar() in order to write characters out to the 
console, and yet one of them works in a graphical terminal and one of 
them doesn't...



Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
t: +44 870 608 0063

Sirius Labs: http://www.siriusit.co.uk/labs

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