Teensy 3.1 need to output 8mhz clock on digital pin

[renasis]

Hello,

Does anybody know how to produce an output clock on a digital pin(on a pin other than the spi clock pin) with a frequency of 8 mhz?

Thanks,

-ren

 

[potatotron]

Typing this from my work computer, without access to an actual Teensy, but how about something like this:

IntervalTimer myTimer;

const int clockPin = XX;

void setup(void) {
  pinMode(clockPin, OUTPUT);
  myTimer.begin(Clocker, 0.125);
  }

void loop(void) {
  }

void Clocker(void) {
  static int state = LOW;

  if (state==LOW) {
    state=HIGH;
    digitalWriteFast(clockPin, HIGH);
    }
  else {
    state=LOW;
    digitalWriteFast(clockPin, LOW);
    }
  }

 

[stevech]

Isn't there a way to have a hardware timer toggle a pin on overflow?
So no software overhead needed.
I did this on the AVRs, for 38KHz.

 

[Demolishun]

Actually I saw an article somewhere on doing this with DMA transfers. It talked about creating really fast clock outputs by setting up continuous DMA transfers to a port. You will have to search, but it was ARM related and was related to the micro class used with the Teensy 3.1.

Edit:
Ooh! I bookmarked it!
http://mcuoneclipse.com/2014/06/07/tutorial-pwm-with-dma-on-armkinetis/

 

[renasis]

Thanks for the replies,

potatotron thanks for the code, lowest interval that I could get to work was microseconds=1, output was 290kHz@24mhz system clock or 500kHz @ 48mhz/96mhz system clock. I specified like so myTimer.begin(Clocker, 1). Based on the documentation it looks like I should be able specify a fractional interval(.125), but I cannot get any output. Tested on pin 13.

Demolishun, interesting, but I would prefer a simpler approach, something along the lines of what stevech suggested, if possible. Thanks for the link though, I will investigate it further when I get a chance.

-ren

 

[PaulStoffregen]

I believe this is the easiest way

void setup() {
  analogWriteFrequency(4, 8000000);
  analogWrite(4, 128);
}
void loop() {
}

(click for full size)

 

[renasis]

Paul,

Thanks, that works well. Can you use this same technique to create a 16mhz clock?

Thanks,

-ren

 

[PaulStoffregen]

Yes, since the peripheral clock is 48 MHz when the CPU runs at 48 or 96 MHz, but you can't get a 50% duty cycle.

 

[renasis]

Paul,

Any chance you could give me an example at 16mhz, I am having trouble determining the correct parameters.

Also, I was curious if you might be familiar with the code below. This is from Freescale app AN4627(zip file AN4627SW). This is to create a 24mhz clock. The faster the clock output I can generate, the better. So, of course, my next question would be, how could I get an output clock of 24mhz? I tried using the code in a sketch, in the setup function, but the width between the pulses vary. I suspect that this might be due to T3.1 onload init functions.

//#define FTM_24MHZ_PERIOD (0x00000001UL)
//#define FTM_24MHZ_DUTY (0x00000001UL)

void Set_FTM0(void)
{
SIM_SCGC6 |= SIM_SCGC6_FTM0_MASK; // Enable clock for FTM0
PORTC_PCR1 = PORT_PCR_MUX(0x04)|PORT_PCR_DSE_MASK; // Define pin for FTM0
FTM0_MOD = FTM_24MHZ_PERIOD; // PWM period
// Configure timers for edge aligned PWM High True Pulses
FTM0_C0SC = 0x28; // No Interrupts; High True pulses on Edge Aligned PWM
FTM0_C0V = FTM_24MHZ_DUTY; // 50% pulse width
FTM0_SC = 0x08; // Edge Aligned PWM running from BUSCLK / 1
}

Thanks,

-ren