Fun in real time
Greg
Bollella, the real-time lead at Sun has convinced a few of us
to help him out with his
Slot Car Programming Challenge for
JavaOne this year. This is a picture of him assembling a slot car
track on an 8'x16' table. The cars that run on track are absolutely
standard 1/24 scale cars. No mods. The track has 80 sensors spread
along its length. Instead of a manual control, the power supply is
controlled by an A/D converter driven from a workstation. The
challenge is to write software to control the car and get around
the track as fast as possible. This is a pretty tricky problem
since entries will have to get the timing of the power changes
exactly right. It's doubly tricky because the sensors are fairly
primitive (which is very common in actual realtime systems). These
sensors are simple photocell gates (the kind used to detect paper
moving through a printer) placed along the slot. They give a simple
0/1 indication of whether or not the car is passing by the sensor.
To make life harder, all of the sensors are
ored together.
There's only 1 bit of input - two, actually - one sensor gets's a
seperate bit: it's the start/finish line. So you have to count.
Accuratly. No missing sensor pulses. A map of the course will be
provided. One of the bonus features is that the power supply can
swing it's voltage pretty quickly - even going into reverse. So
there are lots of tricks to be done involving rapid braking, or
pulsing. It's remarkably easy to send the car flying off the
corners.
