122-32000 Parallax Inc, 122-32000 Datasheet - Page 164

• Manufacturer Part Number: 122-32000
• Description: MANUAL PROPELLER
• Manufacturer: Parallax Inc

Specifications of 122-32000

• Accessory Type: Manual
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The above example shows three methods of various logical levels,
(“mid-level”) and
maker of the application; deciding how to respond to events like sensor activations and motor
movements.
distance. The low-level method,
properly and verifying that it is successful.
In an application like this, critical events could occur in low-level code that needs to be
addressed by high-level code. The
message to the high-level code without requiring complicated message-passing code for all
the mid-level code in-between. In this case, we have only one mid-level method but there
could be many nested mid-level methods between the high-level and the low-level.
The
statement. It then calls
The
successfully completes,
complication of moving the robot’s motors to achieve the desired direction, but if it
determines the motors are stuck, it cannot move them further and it aborts with a
Otherwise it simply returns normally.
If everything is fine, the
normally and eventually returns
however,
stack all the way through the
was found.
terminated. The
FALSE
stack) and it decides to
If we had not put the Abort Trap, (
the call stack would have been popped until it was empty and this application would have
terminated immediately.
Page 164 · Propeller Manual v1.0
<more code>
Main
Move
value that was actually returned by the aborted
method gets sensor inputs and decides what direction to move the robot via the
DriveMotors
method sets its
– Spin Language Reference
The
The mid-level method,
Main
DriveMotors
Move
method checks the value returned by its call to
finds a problem, it
Beep
Move
method is completely oblivious to this and is now effectively
DriveMotors
RESULT
Move
as a result of the detected failure.
in a special way, with the Abort Trap symbol,
Move
(“low-level”). The high-level method,
returns
to
TRUE
\
method and up to the
DriveMotors
), in front of the call to
TRUE
ABORT
method returns normally, the
, and the
Move
TRUE
and then calls
ABORT
, is responsible for moving the robot a short
command can be instrumental in getting the
.
, handles the details of driving the motors
s which causes the Propeller to pop the call
Main
The
DriveMotors
method continues on normally. If,
DriveMotors
DriveMotors
Main
Move
method where the Abort Trap
, when
method deep down the call
Main
Move
Move
in a finite loop. If it
method handles the
DriveMotors
Main
(“high-level”),
method carries on
(which is now the
, is the decision
\
, preceding it.
FALSE
aborted,
value.
Move
CASE