Multiple PWM Outputs with Unique Frequencies

Hardware Arduino Due
14

randomvibe:
Okay, I finally came up with a clean alternate approach for setting up PWM frequencies from within a sketch, for up to two unique frequencies. The trick is to utilize the two PWM clocks (CLKA & CLKB) provided by the SAM3X8E chip.

I wrote and enclosed a library (pwm01.h). It includes 4 user functions to: 1) setup PWM resolution, 2) setup PWM pin, frequency & pick clock, 3) write duty cycle, and 4) stop PWM. See example code for usage:

#include "C:\Programs\arduino-1.5.1r2\hardware\arduino\sam\libraries\Pwm01\pwm01.h"

void setup()
{
   uint32_t  pwm_duty = 32767;
   uint32_t  pwm_freq1 = 2;  
   uint32_t  pwm_freq2 = 5000;

// Set PWM Resolution
   pwm_set_resolution(16);

// Setup PWM Once (Up to two unique frequencies allowed
   //-----------------------------------------------------    
   pwm_setup( 6, pwm_freq1, 1);  // Pin 6 freq set to "pwm_freq1" on clock A
   pwm_setup( 7, pwm_freq2, 2);  // Pin 7 freq set to "pwm_freq2" on clock B
   pwm_setup( 8, pwm_freq2, 2);  // Pin 8 freq set to "pwm_freq2" on clock B
   pwm_setup( 9, pwm_freq2, 2);  // Pin 9 freq set to "pwm_freq2" on clock B
     
   // Write PWM Duty Cycle Anytime After PWM Setup
   //-----------------------------------------------------    
   pwm_write_duty( 6, pwm_duty );  // 50% duty cycle on Pin 6
   pwm_write_duty( 7, pwm_duty );  // 50% duty cycle on Pin 7
   pwm_write_duty( 8, pwm_duty );  // 50% duty cycle on Pin 8
   pwm_write_duty( 9, pwm_duty );  // 50% duty cycle on Pin 9

delay(30000);  // 30sec Delay; PWM signal will still stream
       
   // Force PWM Stop On All Pins
   //-----------------------------    
   pwm_stop( 6 );
   pwm_stop( 7 );
   pwm_stop( 8 );
   pwm_stop( 9 );
}

void loop()
{  
}





The pwm01.h library and example code were tested in IDE 1.5.1r2. Additional notes on this library:
- Applies to Arduino-Due board, PWM pins 6, 7, 8 & 9.
- Libary Does not operate on the TIO pins.
- Unique frequencies set via PWM Clock-A ("CLKA") and Clock-B ("CLKB")
Therefore, up to two unique frequencies allowed.
- Set max duty cycle counts (pwm_max_duty_Ncount) equal to 255 per Arduino approach. 
This value is best SUITED for low frequency applications (2hz to 40,000hz) such as
PWM motor drivers, 38khz infrared transmitters, etc.
- Future library versions will address high frequency applications.
- Arduino's "wiring_analog.c" function was very helpful in this effort.

Dear randomvibe, I'm grateful for this library. I'm testing it on my Arduino Due, it works great but I'm facing an issue about frequency; for example, if I set:
uint32_t pwm_freq1=1000;
then on pin 6 my (old) oscilloscope measures more or less 200Hz. So: either my oscilloscope is too old, or I'm missing something...
Thanks