From:	"Gordon Hogenson" <gordon AT yrd DOT chem DOT washington DOT edu>
Date:	Sat, 16 Apr 1994 23:37:52 -0700
To:	djgpp AT sun DOT soe DOT clarkson DOT edu
Subject:	Fatal DOS Memory error using _go32_simulate_int

Ok, in response to DJ's comments (thanks, DJ!), I'm using the
transfer buffer to transfer to DOS memory, setting and
reading the palette.  Now I've gone on to tackle another
BIOS call, the "load custom character font" call.
Unfortunately, using *either* the transfer buffer method, or
the _go32_dpmi_allocate_dos_memory method, the system self-reboots
when I run my program.

If I single step through the program (under edebug32) I can get all the
way through!  But, as soon as I exit from the debugger (it says my
program has terminated normally), I get an error from 4DOS:

4DOS server error -- Memory allocation error.
Fatal error--please reboot.

Humph!  So I ask, what should I be watching for in the debugger assembly
code that could cause a 'memory allocation error'.  Am I not using the
go32 functions correctly?

-------------------------------------------------------------------
/* buf is a ptr to k 32-byte blocks, representing characters.
 * this procedure writes k characters into the char table starting
 * at offset
 */

write_char_gen(unsigned char* buf, unsigned short k, unsigned short offset)
{
  _go32_dpmi_registers r;

  unsigned long xfer_buf_addr = _go32_info_block.
                linear_address_of_transfer_buffer;
  unsigned short xfer_buf_offset = xfer_buf_addr % 16;
  unsigned short xfer_buf_seg = xfer_buf_addr / 16;

  dosmemput(buf, k*32, xfer_buf_addr);
  r.x.es = xfer_buf_seg;
  r.x.bp = xfer_buf_offset;
  r.h.ah = 0x11;                /* Load Character Generator */
  r.h.al = 0;                   /* 0x10 if you want timing recomputed */
  r.x.cx = k;
  r.x.dx = offset;
  r.h.bh = 16;                  /* number of bytes per char : VGA=16 */
  r.h.bl = 0;                   /* which char set (0-7) */
  _go32_dpmi_simulate_int(0x10, &r);

}


int main()
{
  unsigned char buf[32];
  memset(buf, 0xFF, 16);
  memset(buf+16, 0x00, 16);
  write_char_gen(buf, 1, 65);  /* should replace 'A' with a solid block */
}


This is run from 80x25 mode. Since the custom character set is stored in
plane 2 of display memory, is there something wrong with having the BIOS
modify that memory from a protected mode program??  Or am I missing something
obvious?

Gordon


--
----------------------------------------------------------------
Gordon J. Hogenson			Tel. (206) 522-5664 home
email: ghogenso AT u DOT washington DOT edu	     (206) 685-2951 work
finger: gordon AT yrd DOT chem DOT washington DOT edu	FAX: (206) 685-8665

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