User guide

6: ICP Software
DC 900-1338I 103
4. XIO posts a write to the Write Request Queue associated with the node identified
in the host request header.
5. When the ICP’s host sends a read request to its driver with a matching node num-
ber, XIO transfers the message from the data buffer to the ICP’s host memory and
the ICP write request issued in step 3 is complete.
6. As instructed by the disposition flags, XIO releases the header and data buffers to
their respective partitions.
6.2 Control of Transmit and Receive Operations
Various techniques are available for coordinating transmit and receive operations at the
task and interrupt level. The simplest method is to start every operation from the task
level. In this case, a signal of some kind must be sent from the interrupt service routine
to the task level at completion, at which time the task can start the next operation. This
is the method used by the SPS for data transmissions.
Another option is to maintain a queue of messages. To save time in the interrupt service
routine, messages can be added to the tail and removed from the head of the queue at
the task level, with the interrupt service routine moving from message to message
within the queue using a
link field in the buffer headers. An example of this technique is
provided by the SPS receive operations.
The following sections describe the task/interrupt-service-routine interface used to
control transmit and receive operations for the SPS.