Why do you want to implement an ISR on a PWM pin?
I mean, ISRs are used on input pins when a specific action takes place and it triggers certain interruption. Why do you want to use it on a PWM pin? I mean if you set a pin as PWM it is an output pin.
I am trying to implement a timer in the intel edison on eclipse. I want to have two functions running, one reading an I2C value continuously and the other, gets the value from the I2C every 10 seconds and then send it to a PWM pin which controls my motor speed. I thought that the only way to do that is to invoke an interrupt on the PWM pin every 10 seconds. Is there a way to implement the CPU timer/RTOS of the edison to call the PWM function every 10 seconds?
Why don't you use a timer instead of using interruptions, check this document about the same subject: Create your own timer routine in Linux | My Linux and Telecom Experiences I believe it may be able to help you achieve your project.