[georgevigelette]

After every bare-metal (ROM DFU) update the sensor module dropped off USB and stayed off until it was power-cycled; the console, same MCU, restarts.

The STM32 ROM loader scans its UART interfaces as well as USB. On the sensor board PB15, USART1_RX for the ROM, is camera 4's UART TX line, and with camera 4 unpowered it sits low. The DFU-request reset leaves every camera rail off, so the ROM sees a low RX line, commits to its UART protocol and waits for the 0x7F auto-baud byte forever. USB DFU still works, but the DFU leave request is never acted on.

Bench evidence (right module, 2026-10-15): with no erase or download, a plain DFU enter + leave hung every time with the core in the ROM's USART1 ABRF poll, USART1 framing error latched and PB15 low. PB15 reads low with camera 4 off and high with it on (CAM_PWR_5, PD3). Powering the cameras from the host before the DFU request does not help: the reset drops the rails before the ROM starts.

CheckBootloaderFlag now switches camera 4's rail on and waits (bounded) for the line to idle high before jumping into the ROM. Registers only, since SysTick and HAL are already torn down there. With this build: 3/3 plain enter + leave restarted, and SDK bare-metal updates fix->fix, fix->fix and fix->1.8.1 all came back about 3 s after the write with no power cycle.

An update away from an image without this fix (1.8.3-rc.1 and older bare metal) still needs a power cycle, because the running image does the ROM entry. Bootloader builds are not affected: they never enter the ROM loader.

Summary

Licensing layer

• Apache-2.0 extension (3D Slicer, wellness/veterinary module, partner SDK, language binding)
• AGPL-3.0 core (firmware, sensing/beamforming/reconstruction/signal-processing/calibration algorithms, hardware reference design)
• Docs / data / tooling only
• This PR moves a file between the AGPL core and the Apache layer — if checked, this is NOT an ordinary PR: it requires the license-manifest change process (and board approval for anything leaving the core). Link the approval.

Checklist

• Commits are signed off (DCO): git commit -s
• New files carry the correct SPDX-License-Identifier for their layer
• Tests and docs updated
• No incompatible third-party code introduced
• CI is green and CODEOWNERS review requested

Notes for reviewers