PropBasic Counters & Servos

skynugget · 2011-10-24 19:24

Hello All!

i am trying to emulate JonnyMacs neat way of driving multiple servos with the system counter (jm_servo8_adv.spin) in PropBasic. Here is what i came up with so far, and it "kind of" works, but there is no real tourqe on the servo turn, and it chatters like a mofo when it gets to the target location.

i suspect my math for the timing is off, does anything see anything wrong with this?

thanks in advance!

kuroneko · 2011-10-24 20:06

Which version of the compiler are you using? With 1.14 stuff like 2500 * us001 gets mistranslated. BTW, us001 should be 80 not 5 for your setup. The code generated is (us001 == 80):

mov     tmp,_2500           '    tmp = 2500 * us001
shl     tmp,#4

This basically messes up your timing.

skynugget · 2011-10-24 20:19

thanks for the heads up kuroneko, ill try that when i get back to the the compiler. im using v1.25

kuroneko · 2011-10-24 20:25

Do you have a link for 1.25?

skynugget · 2011-10-24 20:38

http://forums.parallax.com/attachment.php?attachmentid=85885&d=1318421129

from this post:
http://forums.parallax.com/showthread.php?135098-PropBasic-Bug

kuroneko · 2011-10-24 20:57

Thanks, but that doesn't generate any output for me (1.14 generates 2 SPIN files). I tried two different machines (XP and Vista, JPN) and both come up empty. Anyway, if you can find a way to inspect the generated code have a look at the 2500 * us001 line.

skynugget · 2011-10-24 21:18

odd, are you using bst? i don't think this version will work as it doesn't have the hooks, its straight from Bean. ive been using viewport and cedit to compile with this version.

kuroneko · 2011-10-24 21:23

skynugget wrote: »

odd, are you using bst?

Initially I used it from the command line (which works for the 1.14 release). Then I tried bst and it died (as expected). Maybe it's tied to viewport in a way and requires a specific environment. Beats me.

So in order to check if the same bug is still present you could multiply by 80 manually (*5*16):

tmp = pos << 2    ' *4
      tmp = tmp + pos   ' *5
      tmp = tmp << 4    ' *80

And the other location could just load 200000 (2500*80) directly.

skynugget · 2011-10-24 21:39

ha i just realized i based all my math on 5mhz instead of 80, i guess i just had the crystal value stuck in my head! still playing around so far.
here is what is generated:

 mov           tmp,_2500                    '    tmp = 2500 * us001
                  mov           __temp1,tmp                 
                  shl           tmp,#4

kuroneko · 2011-10-24 22:24

Just remembered something re: [thread=134729]multiply with constants[/thread] (outstanding bug). When you move us001 into a variable first then it should generate proper multiply code, e.g.

tmp = us001
tmp = pos * tmp

skynugget · 2011-10-25 12:28

got the task timing all the servos now! il post up the rest once i have time to get the subs done, thanks!

' ----- TASK Variables (LONG only) ------------------------------------
us001   con 80 '5   '80_000_000 / 1_000_000 tick per microsecond
so      con 18  'servo offset start at pin 18

idx     var long
outpin  var long

slot    var long
pos     var long
tgt     var long
dlt     var long
tmp     VAR long

' ----- SUB and FUNC Definitions ---------------------------------------
'(2^32)/clkfreq = 4294967296/80_000_000 = 53.6870912
'clkfreq=80_000_000  53.6870912 * 65536 = 3518437.2088832

SrvStart:
  OUTPUT servos
  frqa = 1                      'preset for counter
  phsa = 0
  slot = cnt
  
SrvMain:
  for idx = 0 to 7
    rdlong position(idx), pos   'get chanel position value
    rdlong target(idx), tgt     'get channel target value 
    rdlong delta(idx), dlt      'get speed value
    
    outpin = idx + so           'set servo pin via offset 
    COUNTERA 32,outpin          'start counter
      tmp = pos * us001          
      phsa = -tmp 
      
    if pos < tgt then           'is pos less the taget pos?
      pos = pos + dlt 
      pos = pos max tgt
    elseif pos > tgt then
      pos = pos - dlt
      pos = pos min tgt
    endif
  
    tmp = 2500 * us001           'slot timing
    slot = slot + tmp
    WAITCNT slot                'wait for slot to finish
  
    ctra = 0
    wrlong position(idx), pos   'put channel poition value
  next
  goto srvmain                  'loop

ENDTASK

skynugget · 2011-11-12 10:29

here is what i ended up with. it seems to work rather well except for one bug i can't seem to figure out.

if you the first set_servo you use has a speed other then 0, the servo will swing all the way to the srvmin pos at full speed, then will turn to the requested position at the requested speed. i got around it by just initiating all the servos with no speed control when i start the program.

special thanks to bean, jonnymac, and parallax.

if ya make it better please share!

PropBasic Counters & Servos

Comments