| |
It's not a true realtime interrupt.
Some events may be recognized immediately (e.g. a new "mailbox" message, and
some may be recognized on a 100 millisecond background scan (e.g. a "click"
event).
The event monitoring code does not put the task into a "wait state" until
the event happens. It just defines the branch location that the task should
jump to from whatever code it is currently executing. Frequently, the code
for waiting for an event is a "while" loop with a timer.
Firmware scheduler gives time to all running tasks on a round robin basis.
So, it does not preempt the running processes.
You might think the "set task priority" capability would allow for
pre-emption. I can't remember the exact VI / property to set this but it's
in Robolab and the firmware somewhere. Unfortunately, it is very poorly
documented and what it means is "set the task priority used for allocating
and pre-empting devices (motors, sound) as part of the "acquire" opcode. A
very obscure capability that I suspect is not well used.
If you happen to be using the "Swan firmware" you'll find things much
better. All events are recognized and handled on a near real-time basis;
certainly much faster than in the standard firmware. There's a new capabilty
to "set the task scheduler priority" which provides a true pre-empting
scheduler; higher priority runnable tasks consume all real time and lower
priority tasks only get to execute when any higher priority tasks are in a
non-runnable (e.g. wait for timer or event) state. Unfortunately, this is
not documented and not easily accessible in the current Robolab.
I don't think you'll find any further/better documentation than above.
-----Original Message-----
From: news-gateway@lugnet.com [mailto:news-gateway@lugnet.com]On Behalf
Of Elizabeth Mabrey
Sent: Wednesday, May 18, 2005 11:03 PM
To: lugnet.robotics.rcx.robolab@lugnet.com;
lugnet.robotics.rcx@lugnet.com
Subject: true realtime event?
Hi
I am trying to find out whether the event in Robolab is a truly realtime
interrupt. Once the event is triggered, does it truly preempt the current
running process? Input or suggestion to reading material will be
appreciated.
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Best Regards,
Elizabeth Mabrey Partner
of
Director
LEGO MINDSTORMS
3322 Rt. 22 West, Bldg 4, Ste 402 Robotics Community
Branchburg, NJ 08876
Ph: (908) 595-1010 ; M-F: 10-5; Sat: 11-4
Fax: (908) 891-2026
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Message has 1 Reply:
 | | Re: true realtime event?
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| (...) It does allow some very interesting abilities too. I used it for a line-follower, where three tasks could dynamicly alter their priority depending on what was going on. Another use would be a multi-goal system. For instance, one task could be (...) (20 years ago, 19-May-05, to lugnet.robotics.rcx.robolab, lugnet.robotics.rcx)
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Message is in Reply To:
| | true realtime event?
|
| Hi I am trying to find out whether the event in Robolab is a truly realtime interrupt. Once the event is triggered, does it truly preempt the current running process? Input or suggestion to reading material will be appreciated. ---...--- -------- (...) (20 years ago, 19-May-05, to lugnet.robotics.rcx.robolab, lugnet.robotics.rcx)
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