Set PWM frequency on Arduino Mega using Timer2 in "phase & frequency correct" (mode 5)

Question

Using my Arduino Mega 2560 I am trying to generate a PWM signal where I can change both PWM frequency and Duty Cycle. For that I decided to use Timer2 OC2A output. The code is the following one:

void setup()
{
  // ======================================================
  //    Timer 2 example: Phase and Frequency correct PWM
  // ======================================================
  pinMode(10, OUTPUT);
  TCCR2A = 0;//reset the register
  TCNT2  = 0;

  TCCR2A = 0b10000001;  // COM2A1 COM2A0 COM2B1 COM2B0    -      -    WGM21  WGM20
                        //    1      0      0      0      0      0      0      1
                        // Behavior: PWM on OC2A (Arduino pin 10) ; Waveform generation mode 5 (Phase and Frequency Correct)
                        
  TCCR2B = 0b00001001;  //  FOC2A  FOC2B    -      -    WGM22   CS22   CS21   CS20
                        //    0      0      0      0      1      0      0      1
                        // Behavior: Waveform generation mode 5 (Phase and Frequency Correct) ; Prescaler -> clk/1
                        
  OCRA   = 319;         // TOP value -> defines de PWM frequency (25 kHz)
  OCR2A  = 159;         // duty cycle value (80% of ICR1)
} 

void loop() 
{

}

When I try to compile I get the following error:

PWM_Mega.ino:43:3: note: suggested alternative: 'OCR2A'
   OCRA   = 319;         // TOP value -> defines de PWM frequency (25 kHz)
   ^~~~
   OCR2A
exit status 1
'OCRA' was not declared in this scope

I understand the error is because OCRA is not defined. In the uC datasheet (see picture below), mode 5 TOP, that defines the PWM frequency, is defined using register OCRA but when I put that name into my code, it is not recognized. Does anyone know the name of that register so that I can use it in the code?

enter image description here

Thanks

Answer 1

As you want to change the Timer2 frequency you'll have to sacrifice channel A (unlike Timer1 there is no input capture register, that can be used as TOP value)

The OCRA in the image means OCR2A (OCR2A means: Output Compare Register for timer2 channel A)

Therefore you can use only channel B as PWM output

note: Timer2 is 8b only and values like 319 (0x13F) will overflow into 63 (0x3F)