NAME
       OpenDevice -- request an opening of the serial device.

   SYNOPSIS
       error = OpenDevice("serial.device", unit, ioRequest, flags)
       D0                  A0              D0    A1         D1

        byte opendevice(strptr, ulong, struct ioextser *, ulong);

   FUNCTION
       This is an exec call.  Exec will search for the serial.device, and
       if found, will pass this call on to the device.

       Unless the shared-access bit (bit 5 of io_SerFlags) is set,
       exclusive use is granted and no other access to that unit is
       allowed until the owner closes it.  All the serial-specific fields
       in the ioRequest are initialized to their most recent values (or
       the preferences default, for the first time open).

       If support of 7-wire handshaking (i.e. RS232-C CTS/RTS protocol)
       is required, use the serial.device/sdcmd_setparams command.
        This feature should also be specified at inital OpenDevice() time.

   INPUTS
       "serial.device"        - pointer to literal string "serial.device"
       unit             - Must be zero, or a user setable unit number.
                          (This field is used by multiple port controllers)
                         Zero specifies the default serial port.
       ioRequest        - pointer to an ioRequest block of size io_ExtSerSize
                         to be initialized by the serial.device.
                          (see devices/serial.h for the definition)
                          NOTE use of io_SerFlags (see FUNCTION above)
                IMPORTANT: The ioRequest block MUST be of size io_ExtSerSize,
                           and zeroed (with the exeptions as noted)!
       flags            - Must be zero for future compatibility

   RESULTS
       D0         - same as io_Error
       io_Error  - If the open succeded, then io_error will be null.
                    If the open failed, then io_error will be non-zero.
       io_Device - A pointer to whatever device will handle the calls
                   for this unit.  This pointer may be different depending
                   on what unit is requested.

   BUGS
        If 7-wire handshaking is specified, a timeout "feature" is enabled.
        If the device holds off the computer for more than about 30-60
        seconds, the device will return the write request with the error
        SerErr_TimerErr.  Don't depend on this, however.  If you want a timeout,
        set up the timer.device and wait for either timer, or serial IO to
        complete.

        On open, the serial.device allocates the misc.resource for the
        serial port.  It does not return it until the serial.device is
        expunged from memory.  It should return it when no more openers
        exist.   This code can force a specified device to try and
        expunge.  Of course, if the device is in use nothing will happen:

        #include "exec/types.h"
        #include "exec/execbase.h"
        #include "proto/exec.h"

        void FlushDevice(char *);
        extern struct execbase *sysbase;

        void main()
        {
                FlushDevice("serial.device"); /* or parallel.device */
        }

        /*
         * Attempts to flush the named device out of memory.
         * If it fails, no status is returned; examination of
         * the problem will reveal that information has no
         * valid use after the permit().
         */
        void FlushDevice(name)
        char  *name;
        {
        struct device *result;

            Forbid();
            if( result=(struct device *)findname(&sysbase->devicelist,name) )
                RemDevice(result);
            Permit();
        }


   SEE ALSO
        serial.device/closedevice()
        serial.device/sdcmd_setparams
        devices/serial.h