Servers by jDrones

Copter-4.0.5-rc2 available for beta testing

Hot on the heels of 4.0.5-rc1 we’ve released Copter-4.0.5-rc2 for beta testing and it should be available for download from the ground stations within a few hours of this post.

The changes are in the ReleaseNotes and copied below:

  1. Bug fixes:
    a) Serial/UART DMA race condition that could cause watdog reset fixed (Critical fix)
    b) SBUS output when no RC input fixed (Critical fix)

These are both critical fixes meaning they could easily cause a crash although they are also fairly unlikely for most users.

1a) fixes a potential watchdog reset (i.e. autopilot lockup) to do with serial input/output using DMA (direct memory access). So far we have only seen this occur on an mRo Control Zero F7 with high rates of serial input/output. To be clear, there is nothing wrong with the mRo Control Zero F7 hardware but it may have a hardware combination that makes the issue more likely.

1b) fixes an issue with the SBUS output which could lead to the servos intermittently freezing for a few seconds if no RC input is received. This should only affect users who have SBUS servos connected to the autopilot’s “SBUSo” port (or similar). The most vulnerable users are probably tradition helicopter users with SBUS servos controlling the swash plate.

All beta testing and feedback is greatly appreciated!


Thanks for the update. I have many serial UARTs working in parallel on my complex build with Cube Orange and AC 4.0.4:

  • Telemetry (56 kbaud)
  • GNSS RTK (38 kbaud)
  • Companion (460 kbaud)
  • SimpleBGC gimbal controller (115 kbaud)
  • ADS-B reciever (as part of the standard Cube Orange carrier board)

So how likely / how critical do you think is the serial/UART DMA race condition causing watchdog reset with such a build heavily communicating on several serials in parallel?

Would you recommend me to update to 4.0.5 rc2 immediately even if using a release candidate also is some kind of additional risk? If that drone comes down, 20K $ material + hundreds of hours working on it would be trashed (plus the risk for others that a crash could have).

Servers by jDrones