Prop1 Spin; best method for reflecting a signal

Comments

• JonnyMac Posts: 8,923

  2017-04-20 12:48

  You could use a counter. Set CTRx to POS detect mode to measure the incoming pulse (value will be in system ticks in the PHSx register). When you've seen the 0-1-0 transition on the input pin, you can reconfigure the counter to NCO mode to create the outgoing pulse. Between the two processes you could modify the timing of the output pulse.
  
  If you want this to run autonomously, you could launch this method into a cog (with cognew). It uses CTRA to measure the incoming pulse, CTRB to create the outgoing pulse. I made a note where you can adjust the output pulse value. Since this is a Spin cog, you can use a global variable to drive the adjustment.
  
  Warning: I just woke up and this is not tested.
  

  pri reflect(in, out)                                            ' use cognew() to run
  
    ctra := (%01000 << 26) | in                                   ' POS detect (measure)    
    frqa := 1
    phsa := 0
  
    ctrb := (%00100 << 26) | out                                  ' NCO mode (pulse)
    frqb := 1
    phsb := 0
    dira[out] := 1
  
    repeat
      waitpne(|<in, |<in, 0)                                      ' wait for input low
      phsa := 0                                                   ' clear measurement
      waitpeq(|<in, |<in, 0)                                      ' wait for pulse
      waitpne(|<in, |<in, 0)
  
      { adjust phsa here if needed }
      
      phsb := -phsa                                               ' start output pulse
  
• KeithE Posts: 957

  2017-04-20 15:01 edited 2017-04-20 17:33

  I had asked what I think is a similar question here and Ariba posted a simple method which works well if you can dedicate 4 counters:
  
  http://forums.parallax.com/discussion/163764/simple-question-about-simpleide-and-fdserial-155200-baud#latest
  
  Edited: 4 counters was actually for 2 signals
• Tracy Allen Posts: 6,656

  2017-04-20 16:25

  It's two counters in one cog, and one extra pin, to pass a single pin servo signal through non-inverted. Delay is 3 clock cycles.
  POSFEEDBACK = %01001
  ...
  
  ctra := (POSFEEDBACK<<26)+(dummyPin<<9)+servoInPin
  ctrb := (POSFEEDBACK<<26)+(servoOutPin<<9)+dummyPin
  dira := |<dummyPin + |<servoOutPin
  
• Duane Degn Posts: 10,588

  2017-04-20 19:01 edited 2017-04-20 19:03

  Am I correct in assuming these techniques are limited to two input lines?
  
  FWIW, I use something like the code below with some of my quadcopter projects to pass through lines from a RC receiver.
  

  DAT                     org
  
  DAT enter               mov     statesToShift, inputMask
                          shl     statesToShift, shiftAmount
                          or      dira, statesToShift                
                        
  loop                    mov     statesToShift, ina            ' record states of all pins 
                          and     statesToShift, inputMask      ' ignore all but data pins               
                          shl     statesToShift, shiftAmount   ' shift input bits to output pins
                          mov     outa, statesToShift                
                          jmp     loop
  
  inputMask               long    %1111
  shiftAmount             long    17 ' use appropriate value for your setup
  statesToShift           res     1
  
                          fit
  

  
  This particular code requires the input pins to on lower numbered pins than the output pins but it would certainly be easy to modify the code to use any group of input and output pins.
  
  I think the above loop runs at 4MHz with an 80MHz clock.
  
  Edit: I had an "or" where a "mov" needed be.
• macrobeak Posts: 354

  2017-04-21 10:47

  Jon, Ariba, Tracy, Duane,
  Thank you for your input, much appreciated.
  I suspected there would be some elegant solutions to this task, and you have identified and documented them very clearly.
  The Prop 1 brains trust has delivered again!