LEGO MINDSTORMS Robots, Руководство пользователя, Страница: 167 / 226

Page 184
int motorCommand;
task arbitrate() {
while(true) {
if (cruiseCommand != COMMAND_NONE) motorCommand = cruiseCommand;
if (tagCommand != COMMAND_NONE) motorCommand = tagCommand;
if (avoidCommand != COMMAND_NONE) motorCommand = avoidCommand;
if (taggedCommand != COMMAND_NONE) motorCommand = taggedCommand;
motorControl();
}
}
Note that the order is important. The commands in the end of the list will overwrite the value of
motorCommand
and are thus higher-level behaviors. For example, if both the
cruise
and
tagged
behaviors are attempting to control the robot, the
tagged
behavior takes precedence by subsuming the lower-level behavior,
cruise
.
In this implementation, if no behavior asserts control, then
motorCommand
will be unchanged, and the robot will just continue doing whatever it did before. This isn't an issue, since
cruiseCommand
is always
COMMAND_FORWARD
. However, in a different program, you might want to set
motorCommand
to a default action at the beginning of the
while
loop in
arbitrate()
.
Where the rubber meets the road
The
arbitrate
task hands off the actual dirty work of controlling the motors to a subroutine called
motorControl()
. All
motorControl()
has to do is examine the value of
motorCommand
and set the motors accordingly. Here it is:
sub motorControl() {
if (motorCommand == COMMAND_FORWARD)
OnFwd(OUT_A + OUT_C);
else if (motorCommand == COMMAND_REVERSE)
OnRev(OUT_A + OUT_C);
else if (motorCommand == COMMAND_LEFT) {
OnRev(OUT_A);
OnFwd(OUT_C);
}
else if (motorCommand == COMMAND_RIGHT) {
OnFwd(OUT_A);
OnRev(OUT_C);
}
else if (motorCommand == COMMAND_STOP)
Off(OUT_A + OUT_C);
else if (motorCommand == COMMAND_FLOAT)
Float(OUT_A + OUT_C);
}
The relationship between arbitrate and motorControl is important. At first glance, you might think it makes sense to implement motorControl as a separate