I'm trying to create UART cable for A520F phone with USB type-c. Seems, there is no UART debug modes S8+ either. On Samsung phones with micro USB one may access UART JIG mode with 619K resistor, connected to micro USB ID pin.
How I test:
I can dump MUIC registers. I have raw usb type c plug(mounted on board with solder pads), with cable soldered, which maps usb type c pins on breadboard. So I assemble test scheme and analyze MUIC registers and MUIC linux kernel module log output upon attachment.
What I currently find:
- The receptacle is managed by s2mu004 kernel module. Module is capable to manage non type-c receptacles (see CONFIG_MUIC_S2MU004_NON_USB_C_TYPE option)
- Receptacle has non standard pinout: B12 (considering, A row facing top, B row facing bottom side of the phone) pin is not connected to the ground.
- Device can detect water in usb receptacle, by measuring resistance between B12 pin.
- Device can detect plug attach, with ALL pins unconnected, including GND and VBUS pins. How?
- Attaching 619K resistor to B12 pin results in ADC_JIG_UART_ON value in ADC register, during water detection sequence.
- Attaching 619K resistor to one of CC pins result in no device connected.
- Enter UART mode by attaching resistors should be possible in NON type-c mode. (file s2mu004-muic.c ,lines 2835,2797)
- Device has no USB type-c debug accessory mode(tried both with rd/rd and rp/rp resistors on CC pins) - rd/rd results in OTG mode.
What else can I try? If you were this device developer, how would you hide UART debug mode from users?