Errors While Requesting Service - HP 9000 Series 300 Tutorials Manual

On the other hand, if you call hpib_rqst_srvce while you are Active
Controller, the interface receives the service request sequence from the
computer but does not place an SRQ on the bus as long as you are still Active
Controller. However, if active control is passed to another controller on the
bus, as soon as the interface changes to non-controller it immediately sets SRQ
and readies the specified response data byte for the first serial poll from the
new Active Controller.
When an Active Controller detects an asserted SRQ line, it usually conducts
a parallel poll of devices on the bus to determine which one is requesting
service. The next section discusses how to configure the HP-IB interface card
for correct response to parallel polls.
When an HP-IB device responds to a parallel poll with an I need service
message, the Active Controller then performs a serial poll to determine what
type of service is required. If two or more devices are configured to respond to
a parallel poll on a single data line and the Active Controller detects a service
request on that line, the controller
must
perform a serial poll of all devices that
respond on that line in order to determine which device is requesting service.
Errors While Requesting Service
If any of the following error conditions occurs, hpib_rqst_srvce returns -1:
• Entity identifier eid does not refer to an HP-IB raw interface file.
• Entity identifier eid does not refer to an open file.
• A timeout occurs.
• The interface associated with this eid is locked by another process and
O_NDELAY is set for this eid.
3-60 Controlling the HP-IB Interface