VXI VT1433B, User Manual, Page: 74 / 203

Host Interrupt Handling
When the VT1433B asserts the VME interrupt line, the program will cause the
specified interrupt handler to get called. Typically the interrupt handler routine
will read data from the module and then re-enable VT1433B interrupts with
hpe1432_reenableInterrupt. The call to hpe1432_reenableInterrupt must be done
unless the host is not interested in any more interrupts.
Inside the interrupt handler, almost any VT1433B Host Interface library function
can be called. This works because the Host Interface library disables interrupts
around critical sections of code, ensuring that communication with the VT1433B
module stays consistent. Things that are not valid in the handler are:
q
Calling hpe1432_createChannelGroup to delete a group that is simultaneously
being used by non-interrupt-handler code.
q
Calling one of the read data functions (hpe1432_readRawData or
hpe1432_readFloat64Data), if the non-interrupt-handler code is also calling one of
these functions.
q
Calling hpe1432_init to reset the list of channels that are available to the VT1433B
library.
As is always the case with interrupt handlers, it is easy to introduce bugs into a
program and generally difficult to track them down. Be careful when writing this
function.
Data Gating
Sometimes it is desirable to to monitor data from some input channels and not
others. The function hpe1432_setEnable enables or disables data from an input
channel (or group of channels). If data is enabled, then the data can be read
using hpe1432_blockAvailable and hpe1432_readRawData or
hpe1432_readFloat64Data. If data is disabled, data from the specified channel is
not made available to the host computer.
This parameter can be changed while a measurement is running, to allow the host
computer to look at only some of the data being collected by the VT1433B
module. While data from a channel is disabled the input module continues to
collect data but it is not made available to the host computer. The host can then
switch from looking at some channels to looking at others during the
measurement. In contrast, the function hpe1432_setActive completely enables or
disables a channel and can’t be changed while a measurement is running.
For order tracking measurements this function can be used to switch between
receiving order tracking data ordinary time data or both.
VT1433B Parameters
Some parameters, such as range or coupling, apply to specific channels. When a
channel ID is given to a function that sets a channel-specific parameter, only that
channel is set to the new value.
VT1433B User's Guide
Using the VT1433B
3-36