Technical Q&ADV 05 - Determining Whether a Device Supports Asynchronous I/O (1-July-95)Q How can we determine whether a device supports asynchronous I/O? A The best way to determine if a SCSI device supports asynchronous I/O is to use Gestalt. Check the gestaltSCSI selector to see if the gestaltAsyncSCSI bit is set, as shown below:
#include <Gestalt.h>
Boolean CanDoAsyncSCSI(void)
{
long response;
OSErr err;
err = Gestalt(gestaltSCSI, &response);
if (err) return false;
return (response & (1 << gestaltAsyncSCSI) );
}
There is no Gestalt test currently available for non-SCSI devices. You can
assume that asynchronous calls to a driver will be handled correctly. If the
driver is actually asynchronous, your completion routine is called when the I/O
is finished. If the driver is not asynchronous, the driver returns and calls
your completion routine when the I/O is finished. |