help with pwm code

agfa

i'm trying to troubleshoot a problem with some code and can't seem to pin point the source of the problem. i've posted the code. i know the code is sloppy, but please bear with me. i now know there are better ways to pass variables to assembly, but as an exercise i still wanted to make this work.

i'm trying to combine two 16 bit values to one 32 bit value "pass" to pass to the assembly routine. i believe the problem is with the assembly line "shr left, #16". the problem occures when the variable "left " exceeds decimal 511, or 9 bits. the instruction table on page 350 of the PM shows that the source and destination are 9 bit values but i thought that these could be used as pointers to long variables

edit: oops!·the code is·posted now.

Post Edited (agfa) : 8/23/2008 3:00:18 PM GMT

Erik Friesen

your l and r variables are bytes.

I would do something like this

PUB go | x
  cognew(@entry, @pass)  
  repeat
    repeat x from 0 to 125     'linearly advance x from 0 to 125
      pass.word := x + 406         'left speed increments from 0 to 100%
      pass.word[noparse][[/noparse]0] := 531 - x            'right speed decrements from 100 to 0%
      'pass:=l<<16'+r            'combines the speed values to one variable            
      waitcnt(5_000_000 + cnt)   'wait a little while before next update

DAT
'for audio PWM, fundamental freq which must be out of auditory range (period < 50µS)
        org

entry   mov dira, diraval              'set pins 12 and 13 to output               
        mov ctra, ctraval              'establish counter A mode's  APIN
        mov ctrb, ctrbval              '  "            "  b   "     Apin
        mov frqa, #1                   
        mov frqb, #1                   'set counter to increment 1 each cycle 
        mov time, cnt                 'record current time
        add time, period              'establish next period

:loop   rdword left, par              'set "value" to the address of pass
        mov    value,right
        add    value,#2
        rdword right,value
        waitcnt time, period           'wait until next period

Post Edited (Erik Friesen) : 8/23/2008 4:17:58 PM GMT

Erik Friesen

I have no clue why but the above example does not include the pass.word in the first line even though my edited post shows it.

agfa

duh.·

thanks for looking at it, and for the suggestion.

agfa

edit: could you clarify what the edit problem was?

Post Edited (agfa) : 8/23/2008 4:41:21 PM GMT

Paul Baker

The forums interprets [noparse][[/noparse] 1 ] without spaces between as selecting font size 1, it's so that people who don't use internet explorer can format thier posts.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.