User Manual

17. Timing and Delays

The following timing and delay functions are designed for the Orangutans and 3pi robot, which run at 20 MHz.

They will give different results at other processor frequencies. These functions are not available within the

Arduino environment, which has its own delay functions.

The timing functions use a Timer 2 overflow interrupt (TIMER2_OVF), and Timer 2 is automatically

configured when any OrangutanTime function is called. This means that the timing code will conflict with other

code that uses Timer 2 in an incompatible way. However, the functions here are compatible with the other uses

of Timer 2 within the Pololu library.

The Timer 2 overflow ISR is written in assembly to make it as short as possible. When the Timer 2 overflow

interrupt occurs, your code will be interrupted for a total span of 2.65 µs (this includes the time it takes to jump

into the ISR and the time it takes to return from it) once every 102.4 µs. Once every millisecond, the Timer 2

overflow ISR will take a little bit longer: 3.85 µs instead of the usual 2.65 µs. So in all, maintaining the system

timers takes up approximately 2.5% of your available processing time.

General Note about Timers: The functions in Pololu AVR library will conflict with code that

tries to reconfigure the hardware timers it is relying upon, so if you want to use a timer for some

custom task, you cannot use the portion of the library that relies on that timer. The Pololu AVR

library only uses Timer 0 for motor PWM generation, and it is only used for this purpose on

the Orangutan LV, SV, Baby Orangutan, and 3pi robot, so the Orangutan SVP and X2 can safely

use Timer 0 for any custom task. Timer 1 is used by OrangutanBuzzer for sound generation on

all devices, and it is used by OrangutanServos for servo pulse generation on all devices. Timer

2 is used for motor PWM generation on all devices except Orangutan X2, and it is used by

OrangutanTime to run the system timer on all devices. Additionally, the Orangutan SVP-1284

has a second 16-bit timer, Timer 3, that can safely be used for any custom task (the Pololu AVR

library does not use Timer 3 for anything).

17. Timing and Delays Page 58 of 65