# Controller A USB VBUS Electrical Proof — 2026-07-28

Status: complete
Type: evidence
Updated: 2026-08-01
Next Action: none; retain as diagnostic electrical evidence, not as a production publication requirement
Parent: work/wp/completed/wp-characterize-usb-filex-write-size-durability.md

## Hardware Review

Display-board schematic:
`\\srv-fs\PRT\6520500\6520507_dsp_pcb_schematic.pdf`, revision B,
page 2.

The schematic shows:

- S7G2 `PB00/USBHS_VBUS_EN` drives net `USB_VBUS_EN`;
- `USB_VBUS_EN` controls U10, a TPS2051 USB power-distribution switch;
- U10 switches board `+5V` through PF1, a 0.5 A resettable fuse;
- the switched output feeds J3 pin 1, USB VBUS;
- `USB_OVER_CRNT` returns U10 overcurrent state to the processor.

The generated Synergy configuration assigns PB00 to USBHS0 VBUSEN and selects
active-high polarity. The implemented power-down hook clears VBUSEN; the
power-on hook sets it.

## Diagnostic Build

- Preserved artifact stem:
  `Debug/7520553_SMI_FW_VBUS_DIAG_20260728`
- S-record SHA-256:
  `6B4C591CDD8CEB62C18133EF750DE7491AB79F010E03083321428B9984B3F57F`
- ELF SHA-256:
  `DF0E5DE245BC9BD09FAA7C028D1B3445D12667872069A395CEFAD4769FD59114`
- map SHA-256:
  `BCE7265296B8F41995F25AFBB6CFAE677E034A72934F715760D22E8FC6DA6742`
- Correct isolated managed e2 Debug build: passed.
- Repository check suites: 23/23 passed.
- Program/verify on Controller A J-Link `69664082`: passed.
- Controller SD raw CID:
  `035344535330384780976F0084018559`.

The complete pre-deploy 4 MiB internal flash was captured at:

`work/evidence/hpt-log-store-circular-mirror/controller-a/usb-vbus-electrical-check-20260728/rollback-pre-deploy/internal-flash.bin`

SHA-256:
`1F3E6F49A53B6A4187D0E7FD9ACD2B71B891A022A991273ABC528C05DF32675D`.

## Test

The guarded diagnostic performed no file creation. It issued STOP UNIT,
commanded root-port VBUS off, held it off for 500 controller ticks, restored
VBUS, and waited for fresh enumeration/remount.

Controller telemetry:

- STOP UNIT status: `0`;
- power-down status: `0`;
- power-on status: `0`;
- power-cycle count: `1`;
- disconnect detected: `1` tick;
- VBUS-off duration: `500` ticks;
- remount detected: `276` ticks;
- mounted after test: `1`;
- diagnostic terminal state: complete;
- controller system errors: `0`.

The operator observed that the illuminated USB stick went completely dark for
the full five-second interval and illuminated again after VBUS restoration.
This visual observation, combined with the schematic and controller
disconnect/remount telemetry, proves physical connector-VBUS removal rather
than only a logical USB session reset.

## Disposition

Controller A display-board hardware revision B can physically power-cycle the
USB device without cycling the whole controller. The earlier conclusion that
hardware variant 0 could only perform a logical disconnect is superseded.
The unrelated historical `P4_7` GPIO theory remains incorrect; the actual
control path is the dedicated PB00 USBHS VBUSEN output through TPS2051 U10.
