Marlin: Bed PID values read from EEPROM aren't used if P is equal to DUMMY_PID_VALUE

[Alfrederson]

Took quite a while to find out why my friend's controller wouldn't use his PID values no matter what. Turns out he was using 3000 for his P, and configuration_store.cpp is written in a way that it will only update the thermal manager's values if P isn't the same value as DUMMY_PID_VALUE.

Check:

      //
      // Heated Bed PID
      //
      {
        PID_t pid;
        EEPROM_READ(pid);
        #if ENABLED(PIDTEMPBED)
          if (!validating && pid.Kp != DUMMY_PID_VALUE) {
            // Scale PID values since EEPROM values are unscaled
            thermalManager.temp_bed.pid.Kp = pid.Kp;
            thermalManager.temp_bed.pid.Ki = scalePID_i(pid.Ki);
            thermalManager.temp_bed.pid.Kd = scalePID_d(pid.Kd);
          }
        #endif
      }

You can test this by sending M304 P3000, M500, and then rebooting the board. This is present in both 1.1.x and 2.0.x branches.

[ellensp]

So not a bug, but an undocumented feature.
So should probably display a warning the console and LCD is there is one.

[Alfrederson]

Or just remove the comparison with the dummy pid_value. Someone must have added it to fix a previous bug, but in doing so, created a trap.

[thinkyhead]

We'll change DUMMY_PID_VALUE to NAN. 3000 was never expected. In the meantime use 2999.99.

[github-actions[bot]]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.