BeginIO(ioRequest),deviceNode - start up an I/O process

This is a direct function call to the device. It is intended for more advanced programmers. See exec's DoIO() and SendIO() for the normal method of calling devices.

This function initiates a I/O request made to the serial device. Other than read or write, the functions are performed synchronously, and do not depend on any interrupt handling logic (or it's associated discontinuities), and hence should be performed as IO_QUICK. With some exceptions, reads and writes are merely initiated by BeginIO, and thusly return to the caller as begun, not completed. Completion is signalled via the standard ReplyMsg routine. Multiple requests are handled via FIFO queueing. One exception to this non-QUICK handling of reads and writes is for READS when:

• IO_QUICK bit is set
  
  
• There are no pending read requests
  
  
• There is already enough data in the input buffer to satisfy this I/O Request immediately.
  
  

In this case, the IO_QUICK flag is not cleared, and the request is completed by the time it returns to the caller. There is no ReplyMsg or signal bit activity in this case.

ioRequest

pointer to an I/O Request Block of size io_ExtSerSize (see serial.i for size/definition), containing a valid command in io_Command to process, as well as the command's other required parameters.

deviceNode

pointer to the "serial.device", as found in the IO_DEVICE of the ioRequest.

io_Error

if the BeginIO succeded, then Error will be null. If the BeginIO failed, then the Error will be non-zero. I/O errors won't be reported until the io completes.

devices/serial.h