hwa/st/stm32/examples/04-2-counter-output-fade/main.c

This program fades LED1 (porta,2) using one channel output of a counter.

The counting direction of the counter (up/down) is output on LED2. It can synchronize an oscilloscope to view the PWM signal.

You can direct the output signal to (portb,10) instead of LED2 (porta,3) after having powered its port and the afio. This requires a remapping of the counter that is handled by HWA.

main.c

 
/*  This file is part of the HWA project.
 *  Copyright (c) 2020 Christophe Duparquet.
 *  All rights reserved. Read LICENSE.TXT for details.
 */
 
#include BOARD_H
 
#define AHBHZ           HW_DEVICE_HSIHZ         // AHB frequency
#define COUNTER         counter2
#define CHANNEL         channel3
#define DUTYMAX         100
 
#if HW_ADDRESS(LED2) == -1
#  define LED2          fake
#endif
 
/*  Service the counter IRQ (every overflow or underflow, then the frequency of
 *  the IRQ does not depend on the counting mode of the counter, but the
 *  frequency of the PWM output does): compute the next value of the compare
 *  unit.
 *
 *    Phase 0: increase duty cycle from 0 to DUTYMAX
 *    Phase 1: decrease duty cycle from DUTYMAX to 0 (use ~duty)
 *    Phase 2: off
 *    Phase 3: off
 */
HW_ISR(COUNTER)
{
  static uint16_t       duty ;
  static uint8_t        phase ;
 
  hw( clear, (COUNTER,irq) );
 
  hw( write, LED2, hw(read,(COUNTER,dir))==0 );
 
  if ( phase == 0 )
    hw( write, (COUNTER,CHANNEL), duty );
  else if ( phase == 1 )
    hw( write, (COUNTER,CHANNEL), DUTYMAX-duty );
 
  duty++ ;
 
  if ( duty > DUTYMAX ) {
    duty = 0 ;
    phase = (phase+1) & 3 ;
  }
}
 
 
int main ( )
{
  hwa( begin, reset );
 
  /*  Power the controllers we use
   */
  hwa( power, (LED1,port), on );
  hwa( power, (LED2,port), on );
  hwa( power, COUNTER, on );
  hwa( power, afio, on );
  hwa( commit );
 
  /*  Configure GPIOs
   */
  hwa( configure, LED1, function, (COUNTER,CHANNEL), mode, digital_output );
  hwa( configure, LED2, function, gpio, mode, digital_output );
 
  /* FIXME: no error triggered when setting function gpio and (counter2,channel1) to pa0 */
 
  /*  Configure and start the counter (sms=0, cms=3, opm=0, cen=1)
   */
  hwa( configure, COUNTER,
       clock,     from_apb1_psc,
       direction, updown_loop,
       prescaler, AHBHZ/DUTYMAX/100 - 1,
       reload,    DUTYMAX,
       run,       yes );
 
  /*  Configure the channel used as PWM output
   */
  hwa( configure, (COUNTER,CHANNEL),
       function,  compare,
       level,     clear_on_match_up_set_on_match_down,
       output,    connected );
 
  hwa( commit );
 
  hw( enable, (nvic,COUNTER) );
  hw( enable, (COUNTER,irq) );
 
  /*  Sleep between IRQs.
   */
  for(;;) hw( wait, irq );
}