mirror of
https://github.com/nasa/trick.git
synced 2024-12-21 06:03:10 +00:00
99 lines
4.0 KiB
Markdown
99 lines
4.0 KiB
Markdown
| [Home](/trick) → [Developer Docs](Developer-Docs-Home) → Real-Time Synchronization |
|
|
|------------------------------------------------------------------|
|
|
|
|
# Real-Time Synchronization Design
|
|
|
|
A simulation is "real-time" when it can consistently and repetitively execute
|
|
its scheduled math models to completion within some predetermined interval
|
|
time frame for an indefinite period of time. This predetermined interval
|
|
time frame is referred to as the real-time frame. In this design the real-time
|
|
frame is set equal to the simulation software frame. Real-time is achieved
|
|
by periodically pausing simulation execution at the end of each real-time
|
|
frame. If simulation execution has not finished by the end of each real-time
|
|
frame then this is an overrun. The real-time synchronization capability has
|
|
several user settable options when a simulation overruns. If simulation
|
|
execution finishes before the real-time frame expires, this is an underrun. If
|
|
the simulation is underruning, the real-time synchronization capability allows
|
|
the simulation to "sleep" while waiting for the real-time frame to expire.
|
|
|
|
Real-time synchronization defaults off when initializing the simulation.
|
|
To enable real-time synchronization users or models may call enable() at any
|
|
time during the simulation. To exit real-time synchronization users or
|
|
models may call disable() at any time during the simulation. The actual
|
|
entering or exiting real-time happens at the end of the frame.
|
|
|
|
Listed below are the various modes of operation in a simulation and the
|
|
responsibilities of the real-time synchronization class in each.
|
|
|
|
## Pre-Initialization
|
|
|
|
During pre-initialization the user may specify the behavior of the real-time
|
|
synchronization class during overruns and underruns.
|
|
|
|
1. Set real-time synchronization enabled or disabled.
|
|
1. Set real-time sleep timer enabled or disabled.
|
|
1. Set the maximum number of consecutive overruns allowed. (default 100,000,000)
|
|
1. Set the maximum time allowed for single overruns (default 1e37 seconds)
|
|
1. Set action taken when maximum overruns achieved to freeze/terminate or
|
|
terminate immediately (default terminate immediately)
|
|
|
|
## Initialization and Restart
|
|
|
|
The real-time initialization and restart jobs are designed to be the last
|
|
jobs run before exiting initialization or restart mode.
|
|
|
|
Initialize the underlying hardware.
|
|
|
|
@copydetails Trick::RealtimeSync::initialize(long long , long long )
|
|
Trick::RealtimeSync::initialize(long long , long long )
|
|
|
|
## Start Real-Time
|
|
|
|
@copydetails Trick::RealtimeSync::initialize(long long , long long )
|
|
Trick::RealtimeSync::initialize(long long , long long )
|
|
|
|
## End of Frame
|
|
|
|
At the end of the real-time frame (also the software frame) the
|
|
real-time synchronization class will determine if the simulation is
|
|
underruning or overrunning and take actions to keep simulation time
|
|
and real-time in sync.
|
|
|
|
@copydetails Trick::RealtimeSync::rt_monitor( long long )
|
|
Trick::RealtimeSync::rt_monitor( long long )
|
|
|
|
## Freeze Mode
|
|
|
|
### Freeze Initialization
|
|
|
|
During freeze initialization the real-time synchronization class resets the real-time
|
|
frame to the freeze frame and restarts the real-time clock and timer.
|
|
|
|
@copydetails Trick::RealtimeSync::freeze_init( long long )
|
|
Trick::RealtimeSync::freeze_init( long long )
|
|
|
|
### Freeze Loop
|
|
|
|
During freeze loop processing the real-time synchronization pauses the freeze loop.
|
|
The pause is released when real-time equals the freeze loop period. No checks are
|
|
done for overrunning or underruning a freeze period.
|
|
|
|
@copydetails Trick::RealtimeSync::freeze_pause( long long )
|
|
Trick::RealtimeSync::freeze_pause( long long )
|
|
|
|
### UnFreeze
|
|
|
|
During unfreeze the real-time synchronization class resets the real-time
|
|
frame to the software frame and restarts the real-time clock and timer.
|
|
|
|
@copydetails Trick::RealtimeSync::unfreeze( long long , long long )
|
|
Trick::RealtimeSync::unfreeze( long long , long long )
|
|
|
|
## Shutdown Mode
|
|
|
|
During shutdown, the real-time synchronization class stops the clock and sleep
|
|
timer hardware.
|
|
|
|
@copydetails Trick::RealtimeSync::shutdown()
|
|
Trick::RealtimeSync::shutdown()
|