VXI VT1433B, Руководство пользователя, Страница: 106 / 203

Host Interrupt Handling
When the VT1433B asserts the VME interrupt line, SICL 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
e1432_reenable_interrupt. The call to e1432_reenable_interrupt must be done
unless the host is not interested in any more interrupts.
Inside the interrupt handler, almost any VT1432A 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 e1432_delete_channel_group to delete a group that is simultaneously being
used by non-interrupt-handler code.
q
Calling one of the read data functions (e1432_read_raw_data,
e1432_read_float32_data or e1432_read_float64_data), if the non-interrupt-handler
code is also calling one of these functions.
q
Calling e1432_assign_channel_numbers to reset the list of channels that are
available to the VT1432A 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 monitoring data from some input channels and not others is desirable.
The function e1432_set_enable enables or disables data from an input channel (or
group of channels). If data is enabled, then the data can be read using
e1432_block_available and e1432_read_xxx_data. 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 e1432_set_active 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 User's Guide
The Host Interface Library
4-28