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Denis 'GNUtoo' Carikli, 03/08/2020 06:21 PM


There is an in-depth article covering several Samsung devices in the SamsungSerial page


Device and documentation I/O voltage ID<->GND SOC TX SOC RX switch stock bootloader settings Comments
GT-I9100 510k9 D- D+ MAX8997 UART settings: ttySAC2 115200 8N1
To get the UART enabled at boot with the stock bootloader:
* Power the phone off and remove the battery
* Put a battery in
* Hold the select button
* Plug the UART
* Release the select button
To get the UART enabled at boot with the Replicant 6.0 kernel and the stock bootloader, see the DHylands_SGS2_Console page on the mozilla wiki.
At some point the boot procedure switches to the modem UART, it's probably some linux driver doing that
GT-N7000 510k9 D- D+ UART settings: 115200 8N1
GT-I9100G_CHN_CHN 1.8V8 ? 619k9 D- D+ ? UART settings: 115200 8N1 Very few prints from Xloader, the next bootloader used by Android 2.6.3 doesn't seem to print much
GT-I9300 1.8V1 619 kOhms3 D- D+ MAX776935 UART settings: 115200
To increase verbosity during boot:
* Power off the phone and remove the battery
* Put a battery in
* Press the hold the volume-down button
* Plug the UART and wait for the first lines to be printed
* Release the volume-down button
It gives a shell once Replicant 6 has booted
GT-N7100 ?
GT-N7105 ?
Galaxy Nexus (GT-I9250) 619 kOhms4 D+ D- FSA94807 UART settings:
* By default: ttyFIQ0, 115200 8N1
* After patching Linux: ttyO2, 115200 8N1
See GalaxyNexusI9250SerialConsole for more details.
Nexus S 150 kOhm FSA9480
Optimus Black (P970) 1.8V6 N/A2 DP3T
ODROID-U3, console UART 1.8V connector UART settings: ttySAC1, 115200 8N1
ODROID-U3, IO pins UART 1.8V connector UART settings: ttySAC0, 115200 8N1

1 Measured between USB GND and USB VCC

2 Code is required to use the switch as you need to configure both the MUIC and DP3T switch

3 See The related driver source code

4 See the postmarketOS wiki page on Serial debugging

5 See the driver and the ifixit teardown

6 Reference: OptimusBlackSerial

7 See board-tuna-connector.c fsa9480.c in kernel_samsung_tuna

8 Works, as it was tested on the device. TODO: measure the voltage, as lower UART voltages often works with higher voltage levels.

9 Works, as it was tested on the device. TODO: look the official reference in the driver for it.


Interesting links

  • There is a page on Serial debugging on the postmarketOS wiki that contains information for using the serial port for many smartphones models.
  • mv-uart A serial port adapter with configurable voltages (and GPIOs)
  • DHylands_SGS2_SerialAdapter : A very compact setup but with fixed resistor value.

See also

Updated by Denis 'GNUtoo' Carikli about 4 years ago · 70 revisions

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