Problem with differential counter modules

Enrique

Hello,

I am going through the Propeller Education Kit Labs but coding in C instead of Spin and I have encountered a problem in chapter 7, Counter Modules and Circuit Applications Lab.

I hooked up a LED to pin 4 and another one to pin 5 and I am trying to change their brightness using differential duty mode. When I run the program LED 4 works without any problem but LED 5 doesn't turn on at all. I checked the LED that refuses to cooperate and pin 5 of the Propeller and they both work.

Here is the code

/**
 * @file LedDutySweep.c
 * This is the main LedDutySweep program start point.
 */

/**
 * Main program function.
 */

#include <propeller.h>
#include "pin.h"
#include "counter.h"

int main(void)
{
    const int scale=16777216;
    int duty;
    int delta;

    // Prepare the CTRA register
    ctraSetMode(DUTY_DIFFERENTIAL);
    ctraSetApin(4);
    ctraSetBpin(5);
    pinOutput(4);
    pinOutput(5);

    delta=1;
    duty=100;

    //
    while(1)
    {
        waitcnt(CLKFREQ/100+CNT);
        FRQA=duty*scale;
        duty+=delta;
        if (duty==255)
            delta=-1;
        if (duty==100)
            delta=1;
    }
    
    return 0;
}

I am attaching counter.h and counter.c for those of you who want to duplicate the problem.

Thanks,
Enrique

jazzed

Hi Enrique​.

At first glance I don't see why there would be a problem. I trust that there is an issue of course.

Sorry my programming time is limited today (and any Wednesday). I'll try the example tomorrow if someone else doesn't get to it first.

--Steve

Phil Pilgrim (PhiPi)

I don't know how C handles math overflow during multiplication, but 16777216 (0x1000000) times anything over 127 will produce a negative number, which is okay unless C intervenes. Try just shifting duty left by 24 bits instead and see what happens:

FRQA = duty << 24

-Phil

Enrique

Phil

The shifting didn't help.

Enrique

Phil Pilgrim (PhiPi)

Here's the equivalent program in Spin:

CON

  _clkmode      = xtal1 + pll16x
  _xinfreq      = 5_000_000

  scale         = 16777216

PUB  start | duty, delta

  ctra := %00111 << 26 | 5 << 9 | 4
  dira[4..5]~~
  delta := 1
  duty := 100

  repeat
    waitcnt(clkfreq / 100 + cnt)
    frqa := duty * scale
    duty += delta
    if (duty == 255)
      delta := -1
    if (duty == 100)
      delta := 1

It works on my Prop demo board; but, because the duty cannot go lower than 100, the LED connected to pin 5 glows only very dimly and very briefly. If you let the duty go to zero, your pin 5 LED might show more enthusiasm.

-Phil

Enrique

Phil,

You are right, when I let duty go down to 0 both LEDs work.

Thanks,
Enrique