To Next Page

To Previous Page

Page 140

: seek

forward

0 1 TIMER_SET

BEGIN 2 sensorValue threshold @ 3 - < UNTIL

2 sleep

1 TIMER_GET returnTime !

stop

;

: return

forward

returnTime @ sleep

stop

;

: retrieve

seek

grab

turnAround

return

release

turnAround

;

: Minerva

initialize

calibrate

5 0 DO

retrieve

LOOP

;

The pbFORTH implementation of Minerva's program closely resembles the NQC version of the program presented in Chapter 5.

By the time all the simpler words are defined, the more complex words are simply combinations of the earlier ones. Keep this in mind—I'll describe the words in Minerva's program starting at the

end and returning to the beginning.

The main program word, Minerva, pretty much describes itself. It initializes the RCX, which includes configuring input 3 as a light sensor input. Then it calls calibrate to take an average

reading of the light sensor. Finally, it loops five times, calling retrieve to go pick up something and bring it back.

The retrieve word is also pretty self-explanatory. It calls seek to drive forward and look for an object to pick up. Then grab is called to grab the object. Minerva turns around and heads back

to her starting point with turnAround and return. Then she drops the object, with release, and turns around again with turnAround. With the simpler words defined correctly,

retrieve is a highly readable piece of programming:

: retrieve

seek