Simple device driver
Turning an LED on and off at a fixed rate
Parameters:
- port pin
- rate at which to blink LED
API:
- on(port_pin, rate)
- specifies the port pin (e.g., port D pin 3)
- specifies the rate to use in setting up the timer (what scale?)
- off(port_pin)
Internal state and functions:
- keep track of state (on or off for a particular pin) of each pin
- interrupt service routine to handle timer interrupt
- set up interrupt service routine address