USER’S MANUAL__________________________________________________________________
412 _________________________________________________________________ M211322EN-D
D.5.1 Using the Programmable Callback
Timers
The RT-Ctrl thread is structured around a flexible set of real-time callback
timers. The thread is activated each time the initProcSection method is
called, and it is deactivated when that PROC section is eventually exited.
Thus, real-time control is available whenever live (I,Q) data are also being
acquired and processed.
The rtCtrlCBF_f callback function is customized to handle the real-time
control and sequencing tasks for the current major mode. This routine is
called once at the beginning of each data processing section. It then
performs whatever work needs to be done, and requests that it be called
back at some later time. Up to three independent timing and/or event
criteria can define when the callback occurs, and each can be based on:
- A specified number of counts of a free running 1 MHz counter (clock
time)
- A specified number of trigger pulses (trigger relative time)
- A specified number of external input line transitions (I/O event time)
The callback occurs as soon as the timeout criteria are met for any of the
three timers that are activated. For example, if Timer-0 requests a callback
after five triggers, and Timer-1 requests service after 10000 1 MHz counts,
then at 1 KHz PRF the callback occurs in 5 ms. The callback sequence can
be terminated at any time within the current PROC section by specifying
void criteria for reentry.
Callback routines can request that a new trigger bank be loaded at the
precise instant that the next timer events fire. This special feature is
implemented in hardware on the RVP8/Rx card, and is necessary for
creating alternating trigger patterns that remain completely unaffected by
Linux interrupt latencies. Precise programmable trigger control is an
important application of the RT-Ctrl thread, and is made possible by
having this hardware support at the PCI card level.
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