From: "A.Appleyard" <A DOT APPLEYARD AT fs2 DOT mt DOT umist DOT ac DOT uk>
To: DJGPP AT SUN DOT SOE DOT CLARKSON DOT EDU
Date: Thu, 11 May 1995 13:10:35 BST
Subject: Is there a floppy in the drive?

  I tried the following version. It gave AH = : 0x80 for no floppy, 6 ("floppy
changed") the first time after I put a floppy in, and thereafter 4 ("sector
not found / read error") (not 2 = "address mark not found" as Phelps got). And
always AL = 0 ("no sectors read").
  I then changed the CH and CL lines to:-
    regs.h.ch = 0x01;
    regs.h.cl = 0x01;
  I then got the same for no floppy and for "new floppy", but after that
instead of AH=4 I got strange happenings:-
  One time I got "AH=1, AL=1" and then the system locked tight.
  Another time the screen cleared, and as I took the floppy out the system
rebooted spontaneously.
  It thus seems that "here be dragons" if I try to poke about in the floppy
system myself.

#include <stdio.h>
#include <dpmi.h>
#include <go32.h>
#define uns unsigned
_go32_dpmi_registers cb_regs;
/*-----*//* conventional memory:- */
class c_mem {public: _go32_dpmi_seginfo x;
inline c_mem(int nbytes){x.size=nbytes; _go32_dpmi_allocate_dos_memory(&x);};
inline ~c_mem(){_go32_dpmi_free_dos_memory(&x);};};
/*-----*/
class c_byte_addr;
/*-----*/
class c_byte {public: uns int addr; inline c_byte_addr&adr();};
/*-----*/
class c_byte_addr {public: uns int addr;
inline c_byte_addr(uns int Addr=0){addr=Addr;};
inline c_byte_addr(c_mem m){addr=m.x.rm_segment*16+m.x.rm_offset;};};
/*-----*/
int main() {char disk_buffer[1024]; _go32_dpmi_registers regs;
c_mem XYZ(4096); c_byte_addr buf(XYZ);
regs.h.ah = 0x02; /* BIOS disk read */
regs.h.al = 0x01; /* read one sector */
regs.h.ch = 0x00; /* track zero?? */
regs.h.cl = 0x00; /* sector zero?? */
regs.h.dh = 0x00; /* head zero?? */
regs.h.dl = 0x00; /* drive A?? */
regs.x.bx = buf.addr; /* pointer to buffer???? */
regs.x.es = 0;
regs.x.ss = regs.x.sp = 0;
_go32_dpmi_simulate_int(0x13, &regs); /* call BIOS function */
printf("AH=0x%02x, %1d sectors transferred\n",regs.h.ah,regs.h.al);}