search

Aarhus-University-MPE / ArcticRover

2 stars 0 forks source link

timing using millis #9

Closed grinsted closed 2 years ago

grinsted commented 2 years ago

ArcticRover firmware version

No response

Area(s) with issue?

Other

Steps to reproduce

This is not an error we have yet experienced, so i describe the bug here.

Millis is an integer counter that wraps resets to zero after ~42 days (i believe). When it wraps around comparisons such as this wont behave as extpected.

void HeatingProcess()
{
  if (millis() - lastMillisTempCheck < TEMP_CHECK_PERIOD)
    return;

In this particular place it could actually be critical as this will mean that the heating will "never" turn off.

✔️ Expected Behavior

n/a

❌ Actual Behavior

n/a

grinsted commented 2 years ago

This code may actually be fine according to: https://arduino.stackexchange.com/questions/12587/how-can-i-handle-the-millis-rollover#:~:text=Short%20answer%3A%20do%20not%20try,you%20are%20doing%20something%20wrong.

Atleast if all the types in the comparison are "unsigned longs". In the above snippet is a long instead of an unsigned long. I dont know what effect that has. -Should be tested.

MadsR commented 2 years ago

Correct, unsigned longs will wrap around so the math still checks out, and the timing will work.