Vaisala RVP900, User Manual, Page: 387 / 484

• 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 feature is implemented in hardware on the RVP901 IFDR, 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 IFDR-
level.
C.5.2 Standard Trigger and Antenna Event Example
See the rvp9main/open/rtctrl.c file for the standard RVP code for live trigger control
and angle synchronization.
The example consists of
initProcSection_dflt
and
rtCtrlCBF_trigs_dflt
.
The interrupt latencies are absorbed differently for each case:
• For angle syncing, the expected crossing time is computed based on the location of the
antenna when the callback was entered. If a callback is delayed, a shorter future time is
computed.
• For dual PRF triggers, the next interrupt must be shortened. When the callback is
delayed, the iTimerError field tracks the length of the delay (measured in timer
events).
initProcSection_dflt
This is the default routine for the initial entry into each PROC section. It primarily chooses
the real-time callback responses for the current RVP configuration.
The routine sets up an area of private memory that later controls the real-time activity. See
the calling example in
rvp9main/open/mt_fft.c
.
rtCtrlCBF_trigs_dflt
The real time callback strategies for controlling the trigger generator include:
Appendix C – RVP900 Developer Notes
385