> From: Dan Henderson [mailto:[email protected]]
> Thanks for that Jon. That helps explain this a bit further. I believe the
> base period in the ini is set to 100,000. Not sure if that is nS or u
> value? Can this be change to suit or is it tied to the speed of the system?
Hi Dan,
All of my comments are based on what I think I've learned so far. If anyone
else sees an error please correct me.
It's in nano-seconds and it's pretty big on your system and works out to 10kHz.
That's the max step rate you will get from your system as long as you have the
addf parport.0.reset base-thread. Otherwise the max step rate is half that.
You generally get that value from running the program that tests your system
for latency. The jitter you get from that test will change how accurate that
24uS period actually is.
>From my INI file
BASE_PERIOD = 24000 <-- This is 24,000 nS or 24uS or 0.000024 seconds and
equivalent to 41.6667kHz.
SERVO_PERIOD = 1000000 <-- this is 1 million nano-seconds or 1mS equivalent to
1kHz.
So what does it mean?
>From your HAL file.
loadrt trivkins
loadrt [EMCMOT]EMCMOT base_period_nsec=[EMCMOT]BASE_PERIOD
servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[TRAJ]AXES
loadrt hal_parport cfg="0xe000 out 0xe800 out"
loadrt stepgen step_type=0,0,0
loadrt encoder num_chan=1
loadrt abs count=1
loadrt scale count=1
loadrt lowpass count=1
loadrt near
loadrt pwmgen output_type=1
Inside each of these files is a function called
int rtapi_app_main(void) {...}
In that function the command line arguments like step_type are parsed and
default values are set up. Here's how the Parallel port read function is
configured.
/* make read function name */
rtapi_snprintf(name, sizeof(name), "parport.%d.read", n);
/* export read function */
retval = hal_export_funct(name, read_port,
&(port_data_array[n]),0, 0, comp_id);
with the names of the functions you add later in the HAL file with commands
like:
addf parport.0.read base-thread
each addf function with base-thread as an argument must run to completion in
less than 24uS on my system or there won't be time for anything else. Each
of these programs, generally found in the src/hal or src/emc path.
The ones marked servo-thread run once every SERVO_PERIOD which is set at 1mS.
The PID runs once per 1mS. The stepgen runs every 24uS on my system.
Hopefully this helps. So you know the 'why' rather than just do this and tell
us what happened.
John Dammeyer
>
> On Thu, May 7, 2020 at 6:54 PM John Dammeyer <[email protected]> wrote:
>
> >
> > If you look at the source code for "encoders.c" John Kasunich's excellent
> > documentation says this:
> >
> > "The driver exports variables for each counters inputs and output.
> > It also exports two functions. "encoder.update-counters" must be
> > called in a high speed thread, at least twice the maximum desired
> > count rate. "encoder.capture-position" can be called at a much
> > slower rate, and updates the output variables."
> >
> > So if your encoder provides a quadrature count of 200 lines (800
> > quadrature) and you turn that spindle at 4700 RPM (78.3333RPS) then 800
> > pulses/turn * 78.33333 turns/sec = 62.666KHz so your BASE_PERIOD must be
> > at least 125kHz (8,000 nS)
> >
> > In your working example 1200 RPM is 20 RPS * 800 = 16,000 and twice that
> > is 32,000Hz (31,250 nS BASE_PERIOD).
> > What is your BASE_PERIOD set at in your INI file?
> >
> > Work it backwards. For example my PP HAL file says 24,000nS for the BASE
> > THREAD (41,667kHz). Assuming I have a 200 line encoder on the spindle then
> > 41,667kHz/2=20,8333 and divided by 800 = 26 RPS or 1562 RPM. Since I want
> > to turn my spindle up to 3000 RPM that means either I have to decrease the
> > BASE_PERIOD (increase frequency) or reduce the spindle encoder count to
> > about 100.
> >
> > That means I need no more than 100 slots per rev on a disk. That's doable
> > and from what I've read lots of people can thread with that.
> >
> > And, Sam Sokolik has been able to do rudimentary hex holes (although
> > slowly) with less than that.
> >
> > Now since I have a MESA 7i92H all the numbers will change. I've not yet
> > looked at the MESA software.
> >
> > Haven't even really followed the entire path from a
> > G33.1 Z-0.55 K0.025
> > to the Z axis motion in steps/second tracking spindle RPM.
> >
> > John Dammeyer
> >
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