Timer predicates

The arguments passed to a predicate can take three forms - Input, Output or Both, and are denoted by symbols +, - and ? respect

AgPi also provides Timer based predicates which allow for accurate delay and timing functionalities:

1. delay(+T): Used to apply a delay of t milliseconds.

   • t: Time in milliseconds.

2. delayMicroseconds(+T): Used to apply a delay of t microseconds.

   • t: Time in microseconds.

3. millis(-T): It returns a number (T) representing the number of milliseconds since the program called one of the AgPi functions. It returns an unsigned 32-bit number which wraps after 49 days.

   • T: Time in milliseconds returned by the function.

4. micros(-T): It returns a number representing the number of microseconds since the program called one of the AgPi functions. It returns an unsigned 32-bit number which wraps after approximately 71 minutes.

   • T: Time in microseconds returned by the function.

Example for LED blinking:

• Commect a LED to Raspberry Pi at GPIO pins 1 (HIGH) and 0 (LOW).
• Write the following code in a prolog file(in the working directory).
  Blink_Led
• Now start prolog with sudo permission(very important):
  $ sudo swipl
• Consult the platform_pi.pl using:
  ?- consult('platform_pi.pl').
  This will load all of the Tartarus predicates.
• Execute the command:
  ?- start_peripherals.
• Execute the following command to see the LED blink and the output of millis command on terminal.
  ?- start.