Re: Kulago/Mauch DRO ISA quadrature feedback kit

[Doug Fortune <pentam-at-home.com>]

Matt Shaver wrote:

> > From: Doug Fortune <pentam-at-home.com>
> > Ok, I know there is a limit to how fast you can step a stepper (in rpm).
>
> It's more a problem of the granularity of the frequency control during
> accel/decel ....

> 1. Forget the interrupt idea and use a software timing loop. Much better
> control of the step frequency is possible if moves are mostly planned out in
> advance and a short loop (maybe written in assembly) simply clocks out the
> pulses.

Here it is (only for pentiums, not for 386/486 as they do not have a pentiumtimer.

// pentiumtimer.c   - short program to demonstrate getting the pentiumtimer
//                                    ticks which goes from 0 (bootup) to some big 64 bit
number
//                                     (the 64 bit counter wraps to 0 every 430,000 days
or so)
//                                     I think in 2 ns increments on a 500 Mhz cpu.
//                                     the idea is to precompute the 64 bit value you want
to start
//                                     your code at (which represents a time), set the
interrupt to
//                                     get you there shortly before, then go into a busy
cycle
//                                     until you reach the target 64 bit value
//
//                                     when the second column reaches 2**32, it resets to
0
//                                     and the first column increments by one.
//                                     Thanks to the RTL guys who helped me on this prog.
//gcc pentiumtimer.c -o pentiumtimer -O2 ; ./pentiumtimer

#include <stdio.h>

#ifndef __RDTSC_H
#define __RDTSC_H

  inline long long rdtsc(void)
  {
     union { long L[2]; long long LL; } W;
     asm __volatile__ (".byte 0x0F,0x31" : "=a"(W.L[0]), "=d"(W.L[1]));
     return W.LL;
  }

#endif


main()
{
   unsigned long prev = 0L;
   union { unsigned long L[2];
           unsigned long long LL;
          }X;


        // this delta shows the absolute value (in two longs) and the timing
        // difference (granularity) of two successive calls.

        X.LL = rdtsc();
        printf("cnt %u %u\n", X.L[1], prev = X.L[0]);

        X.LL = rdtsc();
        printf("cnt %u %u delta %u\n", X.L[1], X.L[0], X.L[0] - prev );


}

a quick demo:
./pentiumtimer ;
./pentiumtimer ;
./pentiumtimer ;

> May the torque be with you,

May the torque be with all of us

Doug Fortune