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 Robotics / 435
    Re: RCX Programming Questions and Sensor Ideas —Paul Haas
   (...) Check and set do not have to be atomic, they have to be ordered. The sequence is: Check all flags, when clear, set our flag, check all flags again, if only ours is set, do stuff. 1. You can dedicate a task to managing semaphores. I described (...) (26 years ago, 11-Nov-98, to lugnet.robotics)
   
        Re: RCX Programming Questions and Sensor Ideas —Ben Laurie
   (...) It isn't guaranteed to work, either, though it is likely to in the end. This is because two processes can conspire to always have r31 == 2 when you test for r31 == 1. Cheers, Ben. (26 years ago, 11-Nov-98, to lugnet.robotics)
   
        Re: RCX Programming Questions and Sensor Ideas —Paul Haas
   (...) Oops. I don't know how the scheduler in the RCX works. It might execute 1 opcode from each task in order. If 2 tasks get in sync, then they will never leave the semaphore code as written. Here's a fixed version. I added a random backoff. (...) (...) (26 years ago, 11-Nov-98, to lugnet.robotics)
   
        Re: RCX Programming Questions and Sensor Ideas —Todd Lehman
   (...) Paul, Are you sure you want to sleep before decrementing r31? As written, r31 is always >= 1 during the sleep -- which prevents any other tasks from obtaining a lock on the resource during this sleep time. In other words, once any two tasks (...) (26 years ago, 11-Nov-98, to lugnet.robotics)
   
        Re: RCX Programming Questions and Sensor Ideas —Paul Haas
   (...) I think "oops" applies in this case. Your fix looks correct. (...) It doesn't have to be random, just each task needs a different delay. This is easy, since each task has to run its own version of the code. For task 3 insert 3 noops, for task (...) (26 years ago, 11-Nov-98, to lugnet.robotics)
   
        Re: RCX Programming Questions and Sensor Ideas —Todd Lehman
   (...) Does that support an arbitrary number of tasks? If there are n tasks numbered 1 to n, and task k delays for k cycles on failure, I think you still have to be careful to make sure that the number of tasks n is smaller than the loop overhead h (...) (26 years ago, 11-Nov-98, to lugnet.robotics)
 

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