Halting the core with a debugger, or resetting it while a transaction is
in flight, leaves the sensor's SPI shift register part-way through a
word. Every later access is misaligned, WHO_AM_I reads back 0x00 and
initialisation fails, which is the `sensor=none who=0x00` case in the
field logs.
Toggle chip select around idle bytes to return the device to command
state, then soft reset so the register file starts from defaults
regardless of what the previous image was doing.
This covers the sensor-side wedge. It does not recover a wedged fabric
SPI controller, which a CPU-only debugger reset does not touch and which
was observed to need a board power cycle.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
A cruising vehicle produces almost no specific force and almost no
angular rate, so an inertial rest supervisor declares rest while moving.
The engine trusted that flag, and three circular dependencies then locked
the filter out of GNSS entirely:
- GNSS motion evidence was derived only from accepted fixes, so it
froze exactly when a rejection storm made it the one signal able to
veto a false zero-velocity update.
- The zero-velocity update pinned filter velocity near zero, which kept
eskf_speed_mps() below the rest-detector speed limit and latched the
mistake, and clamped the position covariance to metres while the true
error grew to hundreds.
- Position recovery, the intended escape, was gated on being at rest --
unreachable during the moving divergence that needs it.
Field logs show the result: 91 m from GNSS with a 5 m sigma, every fix
failing the NIS gate, gps_age_ms climbing past 40 s and recoveries=0.
Motion evidence now comes from every fix on its own displacement
baseline; accepted Doppler speed vetoes the zero-velocity update and is
taken from the measurement rather than the update outcome, since a filter
that has drifted far enough to reject it is the case that matters; and
that veto latches until a later fix shows low speed, because an unaided
platform gives no evidence that it has stopped.
Startup calibration is fixed alongside it. One tolerance served both as
the sensor zero-g offset allowance and as the motion gate, so the bench
part's in-spec +28 mg offset consumed 93% of it and left no headroom:
calibration_samples thrashed 0,3,0,4,2,1 and never reached the minimum,
so the engine never left CALIBRATING and no fused location was published
at all. The offset allowance is now applied to the calibration window
mean, where a fixed bias actually shows up, leaving the full tolerance to
reject sustained acceleration.
Rest-detector thresholds move into the per-sensor quality profile and are
sized from a stationary bench capture rather than datasheet noise
densities, which describe the bare part and not this board or bandwidth.
Verified on hardware: calibration completes in ~2 s, 1980 fixes accepted
with 1 rejection, sub-metre sigma, gps_age_ms mean 223 ms.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Wait for every navigation-ready tracking channel in a GPS epoch, remove unlocked channels without a timeout, and keep late joins for the next epoch. Reset PLIC ownership during warm initialization and extend Linux synthetic, integrity, and fake-MMIO regression coverage.
onur cayan
onur