ESC check: Avoid unsigned timestamp underflow in telemtry timeout

[Perrrewi]

Solved Problem

During several flights a warning of ESC telemetry missing appear.

Solution

Changing the logic of the if statement to avoid unsigned int underflow.

Test coverage

Tested on a drone with QGC

Context

The tasks are prioritized and the driver has a higher priority than the commander checks. If anything delays driver, then the difference between the absolute time now and the latest published sample time from the esc status esc_status.timestamp might cause an unsigned integer underflow as the esc_status.timestamp becomes greater than now.

To test this hypothesis a sleep was introduced as below:

with following printout:

By changing the formula as in the commit, the if statement would fail ones the esc_status.timestamp stop being published, and if there is a delay the new line of code will avoid the wrapping of the negative subtraction:

Even with 1 s of sleep there was no telemetry missing message:

[github-actions]

FLASH Analysis

px4_fmu-v5x

    FILE SIZE        VM SIZE    
--------------  -------------- 
-0.0%      -1  [ = ]       0    [Unmapped]
-0.0%     -15  [ = ]       0    .debug_line
  -0.4%     -15  [ = ]       0    ../../src/modules/commander/HealthAndArmingChecks/checks/escCheck.cpp
-0.0%     -36  [ = ]       0    .debug_loc
  -0.0%      -4  [ = ]       0    [section .debug_loc]
  -0.7%     -32  [ = ]       0    ../../src/modules/commander/HealthAndArmingChecks/checks/escCheck.cpp
-0.0%     -52  [ = ]       0    TOTAL

px4_fmu-v6x

    FILE SIZE        VM SIZE    
--------------  -------------- 
-0.0%      -1  [ = ]       0    [Unmapped]
-0.0%     -15  [ = ]       0    .debug_line
  -0.4%     -15  [ = ]       0    ../../src/modules/commander/HealthAndArmingChecks/checks/escCheck.cpp
-0.0%     -36  [ = ]       0    .debug_loc
  -0.0%      -4  [ = ]       0    [section .debug_loc]
  -0.7%     -32  [ = ]       0    ../../src/modules/commander/HealthAndArmingChecks/checks/escCheck.cpp
-0.0%     -52  [ = ]       0    TOTAL

Updated: 2024-12-03T16:18:32

[MaEtUgR]

Thanks for debugging this issue 🙏