pulse counting

muttvac

Hi All, I would like to count low to high transitions on pin 2(I/O 1). Total number of pulse will be displayed on terminal.
Code below. Thanks

Pub Start | pulsecounter

pst.Start(115_200) 'this sets up terminal

CTRA := %01101000000000000000000000000010 ' - pos edge
FRQA := $01 'this is the count of events
PHSA := $01

dira[1] := 0 'make pin 2(P1) an input to receive pulses

repeat
pst.str(string(" CTRA Value = "))
pst.bin(CTRA,32)

pst.str(string(" PHSA Value = "))
pst.bin(PHSA,32)

pst.str(string(" Pulse Count = ")) 'show Pulse Count value
pst.bin(FRQA,32)
pst.newline

JonnyMac

Here's a method that you can call from the main body of the program.

pub count_edges(pin, ms) | t0                                   ' count positive edges for ms milliseconds

  ctra := (%01010 << 26) | pin                                  ' setup counter
  frqa := 1
  phsa := 0
  
  t0 := cnt                                                     ' sync timing
  repeat ms                                                     ' loop                                 
    waitcnt(t0 += (clkfreq / 1000))                             '  delay 1ms

  ctra := 0                                                     ' stop counting

  return phsa

The great thing about the Propeller is that it can test itself. You can create an oscillator with the other counter and connect it to the same pin -- I just did this and it works as expected.

pub freqout(pin, freq)

  ctrb := (%00100 << 26) | pin
  frqb := ($8000_0000 / (clkfreq / freq)) << 1
  phsa := 0
  dira[pin] := 1

muttvac

Thanks JM, I will try it. Appreciate your help.

muttvac

JM will low to high transition come in on pin 2

JonnyMac

Those are methods to plop into your own test program. Call freqout() first to create test pulses on a pin, then call count_edges() with that same pin and the period (in milliseconds) that you want to count.

Here's something you can drop into a program to see that the mechanisms work. You'll need to define an output to display the counts (hertz in this case).

con

  TACH_PIN  = 2

  TEST_FREQ = 10000


var

  long  hertz                                                         
                                                                 
                                                                 
pub main | t                                                         
                                                          
  ctra := (%00100 << 26) | TACH_PIN                             ' generate test frequency
  frqa := ($8000_0000 / (clkfreq / TEST_FREQ)) << 1
  phsa := 0
  dira[TACH_PIN] := 1

  ' count 0->1 transitions

  ctrb := (%01010 << 26) | TACH_PIN                             ' setup counter
  frqb := 1
  phsb := 0

  t := cnt
  repeat
    waitcnt(t += clkfreq)
    hertz := phsb
    phsb := 0

    { display hertz here }

Duane Degn

There are lots of ways to count pulses using a Propeller. The way JonnyMac showed you it probably the best option for this application but there are times when a loop running in assembly will produce a more accurate count if the input signal has noise on it.

I discussed by confusion about differences in pulse counting techniques in this thread. The thread includes code I used to monitor pulses using three different strategies. You might find the code useful for your purposes (though the code JonnyMac posted should do the job just fine).