Cooperative multitasking, Blocking delay timers – Wavetronix Click 500 (programmable controller) (CLK-500) - Developer Guide User Manual

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CHAPTER 6 • TIMERS AND CLOCKS

Note

By default, the interrupt timer is scheduled to fire about 90 times per second. How-
ever, this is not guaranteed because it is not the highest priority interrupt. The OS
has some higher priority interrupts that service other timers and serial direct memory
access transfers.

Cooperative Multitasking

While a single operating mode or task function is executing, it is actually possible to do

some multitasking. In other words, multiple processes can be accomplished at the same

time because of the powerful processor that runs the Click 500.

Using the interrupt timer is one way to accomplish cooperative multitasking. Another way

is to code multiple processes so that they execute based upon non-blocking timers, instead

of blocking delay timer routines. The section below explores the pros and cons of blocking

and non-blocking wait timers.

Blocking Delay Timers

Mode 2 in the code below uses the Click utility ClickUtilPause and ClickUtilCondition-

alPause functions. The ClickUtilPause function is used to provide a delay for a specified

number of milliseconds. The function will return as soon as the specified time has elapsed.

Similarly, the ClickUtilConditionalPause function will delay for a specified amount of time,

but will terminate early if a specified event occurs. The specified event function is called

continuously and an event will occur if the event function returns TRUE. In the code below,

the ClickBtnPressed event function is used so that the wait time will be preempted if the

push-button is pressed.

The pause functions provide a simple way to wait for something external to happen before

the main process continues executing. In the example below, these functions are used to

create a startup delay of several seconds. During the startup time, the red LEDs will be on

and the push-button cannot be used to start and stop the progress indications on the yellow

LED bank. Unfortunately, during the pause time, nothing else can be processed by the main

idle loop. In other words, the UpdateProgress function in this example is “blocked” from

executing until the wait time is reached.

This manual is related to the following products:

Click 510 (communication tester) (CLK-510) - Developer Guide Click 511 (digital I/O repeater) (CLK-511) - Developer Guide Click 512 (vehicle alert) (CLK-512) - Developer Guide Click 513 (traffic alert) (CLK-513) - Developer Guide Click 514 (event logger) (CLK-514) - Developer Guide