Hello all, I am trying to use one-shot timers with the HPET as described in the Intel specs (http://www.intel.com/hardwaredesign/hpetspec_1.pdf). The linux hpet driver (2.6.17.13) has no API to do that (only periodic timers at that time) an I am looking for the best way to add this possibility to the kernel.
At this time I have developed a module that uses hpet_register/hpet_control to get a hpet timer and uses hpet registers to set a one-shot timer and wait for the interrupt. My tests gave strange results : the interrupt comes as soon as I set the interrupt enable bit for the timer. So I made other tests with the original driver (kernel 2.6.17.13) and the demo code in Documentation/hpet.txt and here is what I get: the behavior is different between the first time I launch the test and the others. The following hpet_test polls for 2 interrupt and the frequency is set to 1Hz so the expired time should be around 1000000us but it is only true for the first time I use the timer after a fresh boot : First run after fresh boot : [HPET]# ./hpet_test poll /dev/hpet 1 2 -hpet: executing poll hpet_poll: expired time = 1000008 <=== 1s, good hpet_poll: revents = 1 hpet_poll: data 0x1 hpet_poll: expired time = 999997 <=== 1s, good hpet_poll: revents = 1 hpet_poll: data 0x1 Second run : [HPET]# ./hpet_test poll /dev/hpet 1 2 -hpet: executing poll hpet_poll: expired time = 2 <=== 2us, BAD !!! hpet_poll: revents = 1 hpet_poll: data 0x1 hpet_poll: expired time = 999992 <=== 1s, good hpet_poll: revents = 1 hpet_poll: data 0x1 As you can see, the first run gives 1s for expiration time for the all IT, but all other runs give 2/3 us for first IT !!! If I want to reproduce, I have to reboot. Is this the normal behavior ? It looks like something (driver value, hpet register, ...) is not re-set to the initial parameters. I am trying to find what's wrong in the hpet.c file but I can't figure out at the moment. I also want to add aperiodic/one-shot interrupt possibility to the driver so the the user can tell the hpet timer to send one IT in XXX us from now or from a timeval parameter. But this will only be possible if the previous problem is solved. I have a working module the sets the comparator register with the right value for but the interrupt fires immediately so it is unusable at the time. Thank you in advance for the help. - Sylvain - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
