Dongle probe

Dongle-Lite — KiCad hardware

The USB 2.0 variant of the RecoverKit dongle: an RP2354A + FUSB302B board that forces an Apple Silicon / T2 Mac into DFU over USB-PD, no keyboard dance required. See ../README.md for how the dongle family works and how the Lite compares to the Dongle-Pro, ./PRD.md for the product spec, and ./BOM-sourcing.md for parts sourcing.

How it works (short version)

The host plugs into J1, the target Mac into J2. A CH334F USB 2.0 hub puts two devices on the host's bus: the RP2354A (control + CDC serial for restorekit) and the target itself. The FUSB302B drives the target CC line with Apple's vendor-defined USB-PD messages to flip the Mac into DFU; an AP22653 load switch power-cycles target VBUS for clean re-enumeration; two 74AVC1T45s break out the target's SBU debug UART at 1.2 V. Restore data flows host ↔ target straight through the hub — the MCU only triggers, never proxies.

Status

• Schematic: complete, single sheet, functionally clustered, ERC 0.
• Layout: two builds of the same netlist:
  • dongle-lite.kicad_pcb — original two-sided 4-layer layout (mfg-jlcpcb/).
  • dongle-lite-1s4l.kicad_pcb — single-sided 4-layer relayout for JLCPCB Economic PCBA (mfg-jlcpcb-1s4l/, DRC report checked in). This is the one to order.
• Firmware: ../../crates/dongle-lite-fw (Embassy, rp235xa). The GPIO map lives in the firmware source and matches gen/board.py.

Clusters

One flat sheet (dongle-lite.kicad_sch), five functional clusters — parts that talk to each other are drawn wired together, only cross-cluster signals use labels:

USB D+/D− pairs are impedance-controlled differential pairs on the PCB.

How this was built

Every part is a real LCSC component. Symbols, footprints, and 3D models were pulled with easyeda2kicad into the project-local libraries under lib/ (shared with the Pro via its lib symlink); sym-lib-table / fp-lib-table register them via ${KIPRJMOD}.

The schematic is generated, not hand-drawn: gen/board.py is the authoritative netlist (every part → cluster placement, every pin → net) and gen/gen.py emits the .kicad_sch. Regenerate:

cd hardware/dongle-lite
python3 gen/board.py            # writes dongle-lite.kicad_sch
kicad-cli sch erc dongle-lite.kicad_sch

Key parts (all LCSC)

Full BOM/CPL for ordering are in the mfg-jlcpcb*/ packages.

Hub strap pins

PSELF (18) and RESET#/CDP (16) on U3 are both left open, matching Adafruit's CH334F breakout (product 5997).

PSELF has a built-in pull-up and defaults high = self-powered, which is what makes the hub advertise 500 mA per downstream port. Tied to GND it advertises bus-powered and caps every port at one unit load, 100 mA. A target Mac in DFU fits under that, but every later restore stage asks for 500 mA, so the host refuses to configure the target and the restore dies partway through with a power error. The board still draws from the host's VBUS — this is a declaration, not a supply.

RESET#/CDP is sampled at power-up too: held high it enables CDP (downstream charging-port advertisement) and turns off the hub's low-power sleep. The datasheet wants it "completely suspended when not reset", so there is no pull-up on it.

ERC configuration

pin_not_driven, pin_to_pin, lib_symbol_issues, and lib_symbol_mismatch are set to ignore in the project files: the LCSC-generated symbols type passive/IO pins as "Input/Unspecified", not real disconnections. Everything else keeps default severity.