How serial port initialization delay works

Projects Programming
1

I can't figure out how this feature works.

void setup() {
  /* Initialize serial and wait up to 5 seconds for port to open */
  Serial.begin(9600);
  for(unsigned long const serialBeginTime = millis(); !Serial && (millis() - serialBeginTime > 5000); ) { }

On the first pass, millis() - serialBeginTime will be less than 5000 and, therefore, the loop will exit because the truth condition will be violated.

2

If you want to wait 5 seconds after Serial.begin() before the code continues then why not simply use delay(5000); ?

3

This is an example from the ArduinoIoTCloud library, I wanted to understand how it works.

4

To me it only makes sense if the > is changed to a < sign since both !Serial and
millis()-serialBeginTime > 5000 need to be true for the loop to wait up to 5 seconds for
Serial to be TRUE

5

it's the same as

unsigned long const serialBeginTime = millis();
while (!Serial && (millis() - serialBeginTime > 5000)) {}

which will wait as long as the condition is true.
for a AND condition to be true, you need both to be true
so
➜ Serial needs to be uninitialized
AND
➜ waiting time needs to be more than 5s

ÉDIT: It will exit if one condition is false (which is guaranteed to be the second one immediately)

6

What about when Serial is not initialized, and it has been less than five seconds? How would you ever reach the five second point?

7

Yes it’s crappy code, the second condition is false right away and thus the AND is false and you exit the wait loop.

It was likely meant to be < indeed

8

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.