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TECHNICAL ARTICLE
Figure 1: Try telnet towels.blinkenlights.nl [2]
Listing 1: BlinkWithoutDelay.ino
/* Blink without Delay
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Turns on and off a light emitting diode (LED) connected to a digital
pin, without using the delay() function. This means that other code
can run at the same time without being interrupted by the LED code.
The circuit:
* LED attached from pin 13 to ground
* Note: on most Arduinos, there is already an LED on the board
that’s attached to pin 13, so no hardware is needed for this example.
created 2005
by David A. Mellis
modified 8 Feb 2010
by Paul Stoffregen
This example code is in the public domain
http://www.arduino.cc/en/Tutorial/BlinkWithoutDelay
*/
Figure 2
to understand what you wrote a long time ago. They
(hopefully) explain what the program does, how it
works, or why it’s written the way it is. It’s good practice
to comment on your sketches and to keep the comments
up-to-date when you modify the code. Remember, as a
good ”open-source citizen,” to share your code so others
can learn from or modify/improve your code.
There’s another style for short, single-line comments.
These start with // (e.g on line 26) and continue to the
end of the line.
To delay() or not to delay()? [5]
The delay() function mentioned on line 4 and the hint
not to use it so other code can run already looks weird
to someone who used a RTOS or Unix/Linux before.
Let’s have a closer look at it. From the FreeRTOS call
vTaskDelay(500/portTICK RATE MS) [6], you would
expect to delay a task for 500 msec. The fact that this
API call delays/blocks a task for 500 msec means that
it allows tasks with a lower priority to run until the time
expires.
In Linux usleep(500) [7], it would block the calling
process for 500 msec and allow processes with a lower
priority to run until the time expires – kind of.
Description
The delay() function pauses the program for the amount
of time (in milliseconds) specified as parameter.
(Remember: there are 1000 milliseconds in a second.)
Syntax
delay(ms)
Parameters
ms: the number of milliseconds to pause (unsigned long)
Returns
nothing
(Figure 3)
Caveat
While it is easy to create a blinking LED with the delay()
function, and many sketches use short delays for such
tasks as switch debouncing, the use of delay() in a
sketch has significant drawbacks. No other reading of
sensors, mathematical calculations, or pin manipulation
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TECHNICAL ARTICLE