stepper motor time a bit off

Bits

Below is the code that runs a stepper motor. When I compare the RPMs with a meter I am off slightly. What can I do to improve the time?

RPMs is calculated as
60_000 = msec to minute conversion
20 steps = 1 revolution whole stepping
40 steps = 1 revolution half stepping

60_000 / 40 = 1.5K 'half stepping here
For better resolution I take 1.5K * 100 but then make adjustment in motor object.
= 150_000 / rpms

main object calling the motor object

mot.Control(150_000 / StirSpeed,power) 

The Motor object

Pub Running(_time, _activate) 

  Dira[pin1..pin4]~~
  Time := _Time     
  activate := _activate 


  Repeat  
      IF Activate 
          outa[pin1..pin4] := halfSteps[coil := ++coil // 8]        
          waitcnt((clkfreq / 100_000) * Time + cnt)               
      Else
          outa[pin1..pin4] := $0000 

I think that the IF and Else statements are creating the lag in time. Is there a way to cancel this out?

JonnyMac

What you want to learn to do is create a synchronized delay loop. You do this by grabbing the time at the top of the loop and then offsetting from it; this allows you to control the loop timing. By getting cnt in the loop as you do you're not accounting for loop overhead.

You may ultimately find yourself with something like this:

pri run_stepper(delaypntr, flagpntr) | t, coil

  dira[M1..M4] := %1111                                 ' set coils to output state
  coil := 0                                             ' reset index

  t := cnt                                              ' sync timer
  repeat
    outa[M1..M4] := Half_Steps[coil]                    ' output step pattern
    coil := ++coil & %0111                              ' update step index

    if (long[flagpntr] == true)                         ' still running?
      waitcnt(t += long[delaypntr])                     ' yes, do the delay
    else
      quit                                              ' no, quit the cog 

  outa[M1..M4] := %0000                                 ' clear pins
  dira[M1..M4] := %0000
  
  cogstop(cogid)                                        ' unload the cog

I would tend to want to pass a pointer to the timing value (calculated outside) and a pointer to a flag that allows the cog to unload itself. Of course, you have to start this with cognew.

cognew(run_stepper(@delayustix, @runflag), @stack)

Bits

Thanks Johnny

I used this appnote to solve the problem. Once I found out how many clock cycles it took I recalculated the constant with this


mot.Control(145_325 / StirSpeed,power)
Looking over your code I cant help but ask why you and others clear variables when they are cleared to began with.

You called

pri run_stepper(delaypntr, flagpntr) | t, coil


  dira[M1..M4] := %1111                                 ' set coils to output state
  coil := 0 

Why clear "coil" when this will always be %0 on a new boot. Is it not a local variable?
Thanks none the less for the help

msrobots

Bits,

you are wrong there. The only 'local' variable initialised is RESULT.

all other local variables are NOT initialised by spin but contain whatever is at that stack location from earlier use of that adress.

Enjoy!

Mike

photomankc

Yep, I thought the same thing early on till I spent hours figureing out why a condition kept randomly being 'ignored'. Assuming that the variable was 0 when I entered the function was the reason.