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MOTOR_TASK BUILD

TIMER_TASK BUILD

SENSOR_TASK BUILD

DISPLAY_TASK BUILD

3. Next, you need to actually define what each task does. This is done with the ACTIVATE word, which can be used only inside a definition. Consider, for example, the MOTOR_TASK. Basically,

we want it to look like this:

BEGIN UPDATE_MOTORS PAUSE AGAIN

The real work of the task is in UPDATE_MOTORS, a word that examines some other values in the system and sets the state of the motors. The PAUSE word is the key to cooperative

multitasking-it passes control to the next task in the list. To associate this loop with MOTOR_TASK, we need another special word, ACTIVATE:

:NONAME MOTOR_TASK ACTIVATE BEGIN UPDATE_MOTORS PAUSE AGAIN ; EXECUTE

The ACTIVATE word associates MOTOR_TASK with the rest of the NONAME definition, which is simply the endless BEGIN AGAIN loop. To link the code into the task list, the NONAME

definition is executed. (The combination of NONAME and EXECUTE allows you to execute a defined word just one time. Because it doesn't have a name, you can't execute the defined word

again later.) The tortast.txt example sets up its other three tasks in the same way:

:NONAME TIMER_TASK ACTIVATE BEGIN UPDATE_TIMERS PAUSE AGAIN ; EXECUTE

:NONAME SENSOR_TASK ACTIVATE BEGIN UPDATE_SENSORS PAUSE AGAIN ; EXECUTE

:NONAME DISPLAY_TASK ACTIVATE BEGIN UPDATE_DISPLAY PAUSE AGAIN ; EXECUTE

4. To actually start the tasks running, use AWAKE, like this:

DISPLAY_TASK AWAKE

SENSOR_TASK AWAKE

TIMER_TASK AWAKE

MOTOR_TASK AWAKE

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To dive into this a little more, check out the whole tortask.txt example at the pbFORTH web site.

An Expensive Thermometer

This section contains an example that will help you get your feet wet with pbFORTH. We'll build a simple Celsius thermometer using a temperature sensor. Hook the sensor up to input 2 and enter

the following (I've omitted pbFORTH's ''ok" responses for clarity):

HEX

: buttonState RCX_BUTTON DUP BUTTON_GET @ ;

: isRunButtonPressed buttonState 1 AND ;

: showTemperature

3003 SWAP 3001 LCD_NUMBER

LCD_REFRESH

;

: clear LCD_CLEAR LCD_REFRESH ;

: thermometer

RCX_INIT

SENSOR_INIT