pwm-pin-af.py

# GPIO alternate functions
ALT0 = const(4)
ALT1 = const(5)
ALT5 = const(2)

Pin_AF_PWM = {12:(ALT0,0), 13:(ALT0,1), 18:(ALT5,0), 19:(ALT5,1), \
          40:(ALT0,0), 41:(ALT0,1), 45:(ALT0,1), 52:(ALT1,0), 53:(ALT1,1)} 

def select_PWM_pin(pin):
  if pin in Pin_AF_PWM.keys():
    af, pwm = Pin_AF_PWM[pin]
    reg = 0x20200000 + 4 * (pin // 10)
    bit =  (pin % 10) * 3
    mem32[reg] = (mem32[reg] & ~(7 << bit)) | af << bit
    return pwm
  else:
    return -1