ISR Timing - Embedded

This is a discussion on ISR Timing - Embedded ; Hi All I am facing the strange problem. We are uing the PPC Linux over the MPC860 Board. There is a kernel char driver which interracts with the HW on request from the User Mode Application. ISR routines are written ...

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Thread: ISR Timing

  1. ISR Timing

    Hi All
    I am facing the strange problem.

    We are uing the PPC Linux over the MPC860 Board. There is a kernel char
    driver which interracts with the HW on request from the User Mode
    Application. ISR routines are written in Kernel which sends the signal
    to the User Mode using the Select poll mechanism.

    When I put the printk inside the ISR routine , User Mode Task receives
    the event very fast however on removing the printk it takes a long time
    for the event to be recieved by the user task.

    Can somebody help what the printk is doing ?

    I have Level triggered interrupts and interrupts are disabled in ISR
    and enabled on reading the HW source.

    Thanks in Advance


  2. Re: ISR Timing

    First, it is a bad idea to use printk() inside an isr. You really cannot
    trust any timing the results and you risk the system being locked up. An isr
    runs with the rest of the kernel shut off. You can get some basic debugging
    done that way. A much better way would be to use a trace mechanism.

    Having said that, Let's go to your problem. It is hard to analyze anything
    without seeing source code. You could email it if you don't feel comfortable
    posting it. If it is large, you really can't post it here. There will be a
    fairly simple solution. We just have to find it.

    Bill

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