[avr-gcc-list] ATMega128 Fast PWM

[Thomas D. Dean]

How do I change the polarity of the PWM output, WGM mode 5, OCR1A on the 
fly?

I use WGM mode 5 to provide PWM to drive gearhead motors.  I update the 
OCR values every 50 msec.  The algorithm makes changes gradually.

If, for example, the motor is CCW at 50%, the OCR value is 128.  The 
register values for this are:
(1)
  TCCR1A = _BV(COM1A1) | _BV(WGM10);
  TCCR1B = _BV(WGM12) | _BV(CS11);
  OCR1A = 80;

I want to reverse the direction of the motor.  The register values are:
(2)
  TCCR1A = _BV(COM1A1) | _BV(COM1A0) |_BV(WGM10);
  TCCR1B = _BV(WGM12) | _BV(CS11);
  OCR1A = 80;

The algorithm will slow the motor to stop and then reverse it.  I tried 
setting OCR1A = 0, changing the TCCR1 values, and setting OCR1A = 80. 
This does not work.  After changing from (1) to (2), the PWM stops.

What am I doing wrong?  Any ideas?

Tom Dean

oc-pwm.c
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