On 11/14/2013 2:10 PM, Maximiliano Fermín Córdoba wrote: > > My main goal is to test the beaglebone with linuxcnc in the worst escenario > so as to decide if it is capable of managing the whole system operation. > Maybe the best option is to use an external stepgenerator and use the 'bone > only for the graphical interface and the gcode interpreter. Something like > sending through spi (or something like that) the actual movement and the > external embedded system drive the steppers. > > So my actual drivers are driven with 2usec pulses and I was willing to > generate reliable signals with a max frecuency of 50k. If the jitter is > like the one Im facing now its useless. > > I would really appreciatte your guidance in configuring properly my system.
If you really want 2 uS wide pulses, you'll have to get the PRU task period to be 2 uS or less. That's possible, but I wouldn't run that fast with the default configuration. You can probably pretty safely drop to 5 uS without issue (the 10 uS period is *VERY* conservative), but 2 uS is pushing things without verifying the worst-case PRU task period time. One thing I forgot to ask is how many channels of step/dir you are trying to generate and if you are using the PWM channels. The fewer tasks you have the PRU performing, the shorter you can dial the task period. If you only need 3 step/dir generators, 2 uS is probably reasonable with the existing PRU code, and it will dramatically improve the jitter you're observing with 50 KHz steps. You can control the number of step/dir and PWM generators via the hal_pru_generic command options when loading the driver (the parameters should be fairly self explanatory), and you can add the pru_period= parameter to set the task period to something shorter than the 10 uS default. Let me know how many step/dir channels you need to run, and I'll try to verify how long the PRU task takes to execute (and thus a safe pru_period value). -- Charles Steinkuehler [email protected]
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