On 04/23/2012 02:27 PM, Gilles Chanteperdrix wrote: > On 04/23/2012 01:56 PM, Andrey Nechypurenko wrote: >> Hi Folks, >> >> Following my tests with PWM generation using GPIO in user space [1], >> I've made the RTDM module [2] to further reduce the jitter. As a >> result, jitter was improved, but still under heavy system load the >> servo motor I am trying to control starts shaking. Now, I fill stuck >> and hope to get some help here. >> >> At one hand, I can not imaging that 800MHz ARM (BeagleBoard xM) could >> not manage to generate 20mS PWMs from RTDM driver precise enough to >> avoid sporadic servo movements. So probably I am doing something >> wrong. On the other hand, I do not see where the possible mistake can >> happen and hope that someone experienced in with Xenomai could help. >> >> There is an article about observed behavior [3] with more details, but >> the core problem, I guess, boils down to the following code fragment: >> >> void pwm_task_proc(void *arg) { >> const int which = (int)arg; >> >> // Toggling GPIO pin >> for(;;) { >> //set_data_out has offset 0x94 . Set gpio pin to 1 (up) >> iowrite32(0x40000000, gpio + 0x6094); >> >> // wait requested pulse width time (duty) >> if(0 != rtdm_task_sleep(up_period[which])) >> rtdm_printk("PWM: rtdm_task_sleep() returns error\n"); >> >> //clear_data_out has offset 0x90 . Set gpio pin to 0 (down) >> iowrite32(0x40000000, gpio + 0x6090); >> >> // wait until the next pulse should start (20mS interval) >> if(0 != rtdm_task_wait_period()) >> rtdm_printk("PWM: rtdm_task_wait_period() returns error\n"); >> } >> >> This is the function running as a periodic task started with the following >> call: >> >> retval = rtdm_task_init(&pwm_task[i], // there is currently only one >> element in this array >> "pwm-task", >> pwm_task_proc, >> 0, >> RTDM_TASK_HIGHEST_PRIORITY, >> 20000000); // 20ms period > > Do not use a thread, use a timer. >
So, rtdm_timer_init If this still has too much overhead, you can use the OMAP3 API do dedicate a GPTIMER to this task, and simply register an irq for the GPTIMER which does the job (as opposed to a timer created with rtdm_timer_init). -- Gilles. _______________________________________________ Xenomai-help mailing list Xenomai-help@gna.org https://mail.gna.org/listinfo/xenomai-help