Chapter 3 Software Overview
NI-VXI User Manual
3-46
© National Instruments Corporation
ROAK Versus RORA VXI/VME Interrupters
There are two types of VXI/VME interrupters. The Release On
Acknowledge (ROAK) interrupter is the more common. A ROAK
interrupter automatically unasserts the VXI/VME interrupt line it is
asserting when an interrupt acknowledge cycle on the backplane occurs
on the corresponding level. The VXIbus specification requires that all
message-based devices be ROAK interrupters. It is recommended that
all other types of VXI devices also be ROAK interrupters.
The Release On Register Access (RORA) interrupt is the second type
of VXI/VME interrupter. The RORA interrupter continues to assert the
VXI/VME interrupt line after the interrupt acknowledge cycle is
complete. The RORA interrupter will unassert the interrupt only when
some device-specific interaction is performed. There is no standard
method to cause a RORA interrupter to unassert its interrupt line.
Because a RORA interrupt remains asserted on the backplane, the local
CPU interrupt generation must be inhibited until the device-dependent
acknowledgment is complete.
The function
VXIintAcknowledgeMode
specifies whether a
VXI/VME interrupt level for a particular controller (embedded or
extended) is to be handled as a RORA or ROAK interrupt. If the
VXI/VME interrupt is specified to be handled as a RORA interrupt, the
local CPU automatically inhibits VXI/VME interrupt generation for the
corresponding controller and levels whenever the corresponding
VXI/VME interrupt occurs. After the application has handled and
caused the RORA interrupter to unassert the interrupt line, either
EnableVXIint
or
EnableVXItoSignalInt
must be called to
re-enable local CPU interrupt generation.
The following paragraphs describe the VXI/VME interrupt functions
and default handler. The descriptions are presented at a functional level
describing the operation of each of the functions. The functions are
grouped by area of functionality.
AcknowledgeVXIint (controller, level, statusId)
AcknowledgeVXIint
performs a VXI/VME interrupt acknowledge
(IACK cycle) on the backplane in the specified controller and
VXI/VME interrupt level.
Note:
This function is intended only for debugging purposes.
