The OS/2 PDD reference has some working examples of ioctls for 32-bit
OS/2 code, but none for 16-bit DOS code. It just says "use the DOS INT
21h ioctl interface." It would help to know how!

I google'd for hours without finding a working example. I gave up. But
some time later, I read Ray Gwinn's sio160d\sioref.txt and noticed that
his SIO supports some ioctls, like the original IBM com.sys. And what do
you know, he has a working example of how to call the ioctls from DOS 16
bit code (in assembler). At last, the missing information I needed.

I also learned that IBM's com.sys from MCP2 suports my shared IRQ 2-port
PCI serial card, and backports to WARP 4.

I think I can write a FOSSIL wrapper that loads DOS PCBoard; the key to
making it work is the DOS ioctl interface. I used what I learned from
Ray, and wrote an example in C (Turbo C 2.0+ or Borland C++ 3.1+) that
sets the baud rate. With this interface, you can control all details of
how com.sys works.

I may be the only person on the planet interested in this, but just in
case, here is the code ...


# include 
# include 
# include 
# include 
# include 

typedef unsigned short USHORT;
typedef void VOID;

void
dos440c (USHORT hand, USHORT func, VOID far *parm, VOID far *data)
{
    asm push ds;

    _DS = FP_SEG (data);
    _DX = FP_OFF (data);

    _SI = FP_SEG (parm);
    _DI = FP_OFF (parm);

    _CX = func;
    _BX = hand;
    _AX = 0x440c;

    geninterrupt (0x21);
    asm pop ds;
    if (_FLAGS & 1) {
        ;                               /* error, do something */
    }
}

void
main (void)
{
    int fd;
    unsigned short baud = 19200;

    fd = open ("COM1", O_RDWR);
    if (fd == -1) {
        perror ("failure opening com port");
        exit (EXIT_FAILURE);
    }

    dos440c (fd, 1 << 8 | 0x41, (VOID far *) &baud, (VOID far *) 0);

    close (fd);
    exit (EXIT_SUCCESS);
}

--- PCBoard (R) v15.4/M 250 Beta