Driver Processing

This section describes the driver processing.

In the example, the user process has blocked on the getmsg subroutine while waiting for a message to reach the stream head, and the device driver independently waits for input of a character from the port hardware or for a message from upstream. Upon receipt of an input character interrupt from the port, the driver places the associated character in an M_DATA message, allocated previously. Then, the driver sends the message to the CHARPROC module by calling the CHARPROC upstream put procedure. On return from the CHARPROC module, the driver calls the allocb utility routine to get another message for the next character.