If you use TMR2 as the PWM timebase you can use its postscaler as "divider" between the PWM frequency and interrupt frequency. If you have, say, 16kHz PWM frequency and set the postscaler to 1:16 you'll get an interrupt rate of 1kHz which you can use as a timebase if nothing else you already have running is suitable for that.

Again, there are many ways.....

/Henrik.