Fix: the second gyro is read while the log is paused

[MrScothh]

Follow-up to #11933, which you merged for RC1. Review raised this after the merge and it is right.

What happens

blackboxSetState() turns the secondary gyro on for every state above BLACKBOX_STATE_STOPPED:

gyroSetSecondaryLogging(newState > BLACKBOX_STATE_STOPPED);

That covers more than logging. The header states, BLACKBOX_STATE_PAUSED, which is where a log goes when the blackbox switch is turned off in flight, and BLACKBOX_STATE_SHUTTING_DOWN all write no main frame. A reading taken in any of them goes nowhere, and it costs a transaction on the sensor bus every gyro cycle while it lasts. A pilot who switches logging off mid-flight keeps paying for a sensor nobody reads.

The change

One condition: the second gyro is read while frames are being written, and not otherwise.

gyroSetSecondaryLogging(newState == BLACKBOX_STATE_RUNNING);

Nothing else changes. The zero calibration does not depend on this flag: gyroUpdateSecondary() also reads while !gyroCalibrationComplete[GYRO_SECONDARY], which is what measures the zero at startup, before arming. Stopping and restarting the reads does not re-initialise the sensor, does not restart a calibration and has no settling time, since the device is never reconfigured. The first frame after a resume can carry a reading one gyro cycle old, which is under a millisecond.

Testing

SITL with a counter on the secondary read, armed throughout, toggling the blackbox switch between running and paused:

	before	after
before arming, after calibration	0 reads/s	0 reads/s
armed, logging	76 to 103	38 to 93
armed, log paused	76 to 95	0
armed, logging again	74 to 112	58 to 102
disarmed	0	0

The first second of each phase carries the transition, so it sits between the two rates. Both runs produce a log and both resume cleanly. The zero calibration still runs before arming in both, which is the handful of reads visible there.

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PR Summary by Qodo

Stop Secondary Gyro Reads While Blackbox Logging Is Paused

🐞 Bug fix 🕐 Less than 10 minutes

AI Description

• Enables secondary gyro sampling only while blackbox writes running-state frames.
• Stops wasted sensor-bus transactions during headers, pauses, and shutdown.
• Preserves independent startup calibration reads and clean logging resume.

Diagram

graph TD
    A["State Change"] --> B{"Running State?"}
    B -->|Yes| C["Logging Enabled"] --> D{"Read Needed?"} -->|Yes| G["Read Secondary Gyro"]
    B -->|No| E["Logging Disabled"] --> D
    F["Calibration Pending"] --> D
    D -->|No| H["Skip Bus Read"]

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High-Level Assessment

The exact RUNNING-state check is the best approach because that state directly represents main-frame production. The previous ordinal comparison was overly broad, while coupling sensor control to individual frame-write calls would spread lifecycle responsibility and increase transition risk.

Files changed (1) +5 / -2

Bug fix (1) +5 / -2

blackbox.cRestrict secondary gyro sampling to active frame logging +5/-2

Restrict secondary gyro sampling to active frame logging

• Changes the secondary logging condition from every state above STOPPED to only BLACKBOX_STATE_RUNNING. Expanded comments explain why header, paused, and shutdown states should not spend sensor-bus transactions on unused readings.

src/main/blackbox/blackbox.c