If you load CMPA/CMPB on zero, then use CMPA/CMPB values greater
than or equal to 1.
• If you load CMPA/CMPB on period, then use CMPA/CMPB values less than
or equal to TBPRD-1.
This means there will always be a pulse of at least one TBCLK cycle in a
PWM period which, when very short, tend to be ignored by the system.