4.3 Reverse-engineering USB protocols
Thank you in advance! 🙏
| Error Message | Likely Cause | Solution | |---------------|--------------|----------| | "No device found" | Bootloader not entered | Repeat the shorting method. Measure voltage on PB802’s 3.3V pin. | | "Write timeout" | Poor USB cable or interference | Use a shielded USB 2.0 cable less than 1 meter long. Disable USB selective suspend in Windows power options. | | "Verification failed at offset 0x000400" | Flash chip wear or incorrect firmware base address | Chip may be dying. Try erasing twice. Or use a different firmware version compiled for a different flash offset. | | "Device disappeared during flash" | Brown-out on the PB802 | Power the PB802 via an external 5V supply (not just USB VBUS). The on-board regulator may be failing. | | After flash: still shows "Unknown Device" | Firmware mismatch for the USB controller | You likely flashed SK506S firmware to PB802 or vice versa. The PB802 expects specific USB descriptors. Extract the USB config descriptor from a known good dump. | tp.sk506s.pb802 firmware usb
Most PB802 boards use a generic Vendor ID (VID) of 0x0483 (STMicroelectronics) or 0x10C4 (Silicon Labs). However, in bootloader mode, they often switch to a proprietary VID/PID. | | "Write timeout" | Poor USB cable