• State Not Answered
  • Locked Locked
  • Replies 13 replies
  • Subscribers 22 subscribers
  • Views 1787 views
  • Users 0 members are here
Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

alternate way in absence of get_semaphore_value

Ash J

I am implementing a uart communication, where i have various functions and/or tasks which may want to perform transmission using uart. Hence prior to new transmission on uart, i want to ensure that the resource (uart) is not already in use. this can be achieved by a binary semaphore whose value can be checked prior to new transmissions. But keil RTOS doesnt have sem_getvalue, in absence of which i am unable to think of any way of implementation.

one way around is to have a global flag. But currently trying to use any idea by which i can avoid using a global flag. In case of no other way, will have to use global flag.

any suggestions?

Parents
  • 0 in reply to Ash J

    No - I really do not understand the complications.

    why not:

    while forever {
    wait for mail
    kick-start UART with first character in mail
    wait for event from UART interrupt that UART transmit buffer has been fully consumed
    release mail buffer
}

    And a worker task:

    while forever {
    wait for work
    perform work
    wait for free mail buffer
    send mail with result
}

    Receive task:

    while forever {
    wait for uart data
    process uart data
    if forming command
        if poll command
            wait for free mail buffer
            send mail will poll result
        else
            inform worker thread what to do
}

    Whatever happens, your master processor must be bright enough to not send jobs or ask status requests faster than what the UART channel is able to send back responses or one or more of your threads in the slave processor will not be able to start with the next job because it is still waiting for a mail to use to report the previous result.

Reply
  • 0 in reply to Ash J

    No - I really do not understand the complications.

    why not:

    while forever {
    wait for mail
    kick-start UART with first character in mail
    wait for event from UART interrupt that UART transmit buffer has been fully consumed
    release mail buffer
}

    And a worker task:

    while forever {
    wait for work
    perform work
    wait for free mail buffer
    send mail with result
}

    Receive task:

    while forever {
    wait for uart data
    process uart data
    if forming command
        if poll command
            wait for free mail buffer
            send mail will poll result
        else
            inform worker thread what to do
}

    Whatever happens, your master processor must be bright enough to not send jobs or ask status requests faster than what the UART channel is able to send back responses or one or more of your threads in the slave processor will not be able to start with the next job because it is still waiting for a mail to use to report the previous result.

Children
  • 0 in reply to ImPer Westermark

    Whatever happens, your master processor must be bright enough to not send jobs or ask status requests faster than what the UART channel is able to send back responses...
    this is one of the problem....the master cant be smarter enough as different task at the slave take different amount of time. Though there is some pretty decent amount of delay that master will wait for (100ms or so) before sending a new command or the poll, but there is no estimation of this time period.

    But it appears you really have no idea how that's supposed to be done with the help of a semaphore...
    kindly elaborate how its can be done

    learn what a semaphore is, and what it does.
    suggest some good links or articles that may be noteworthy :)

  • 0 in reply to Ash J

    before sending a new command or the poll,
    in absence of reply from slave...