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thoUART t480 

Signed-off-by: Leah Rowe <info@minifree.org>
master
Leah Rowe 2024-12-29 15:12:25 +00:00
parent aad0b223e0
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1 changed files with 14 additions and 27 deletions
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site/docs/install/t480.md
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@ -356,40 +356,27 @@ the Fn keys for it don't currently work, as of 6 December 2024.
You can set the backlight manually, or use a hotkey, depending on your window
manager or desktop environment.
UART
UART (T480 only. Not T480S)
----
To our knowledge, this functionality is *only* available in coreboot-based
firmware such as Libreboot. It is completely unsupported on the original
firmware!
**NOT supported on the S model (T480s). Please only do it on a T480.**
A serial console is possible via the line-out (headphone jack). Not yet tested
on the T480s (S model), nor implemented, but it is working on the regular
T480 (non-S model).
The EC on ThinkPad T480 has a UART available, and it is enabled in coreboot,
as used by Libreboot. However, you must use a *specific* EC firmware version.
Please read notes elsewhere in this page regarding Lenovo UEFI/EC BIOS updates;
an exact version number is referenced, which you must install prior to Libreboot
installation.
**TODO: show photo and wiring diagram here.**
Ways to flash the EC firmware from Libreboot have not yet been established. Now,
please observe the following photo:
Use baud rate 115200 in your favourite serial terminal client, e.g. GNU Screen.
<img tabindex=1 alt="ThinkPad T480 UART jumpers" class="p" src="https://av.libreboot.org/t480/t480uart.jpg" /><span class="f"><img src="https://av.libreboot.org/t480/t480uart.jpg" /></span>
Next to the headphone jack on the T480, you will find pads for two 0ohm jumpers,
normally unpopulated, but you can bridge each jumper yourself using a 0ohm 0201
jumper; alternatively, simply strip a bit a wire (30awg solid core) and carefully
solder the wire across each of the pad jumpers, then carefully using a pair
of side cutters to cut off the excess wire, being careful not to rip the pads!
You will solder zero-ohm jumps on the indicated footprints. These correspond
to TX and RX, which are connected to the R and L lines on the headphone jack,
respectively; a ground will also be available.
If you do this, please make sure to have the latest EC firmware as of 5
December 2024 (do not use older than what was latest on this day, and don't
use newer versions), because the code for this in coreboot targets a specific
area of code within the EC firmware.
You can then wire a 3.5mm stereo plug. On the other end you will wire your
TX/RX lines as you wish, to a suitable UART adapter; any 3.3v-rated TTL
adapter should work. The Raspberry Pi Pico can be used for this, which is handy
because that can also be used as a serprog-based NOR flasher!
The T480s (S model) schematics is a bit different and the signals are
properly muxed. Note that this is not to be confused with `spkmodem`, which
has not been tested on these boards (but could theoretically be possible too).
You can hook this up to any 3.3v TTL UART dongle, to get a serial console.
Idea for 2nd NVMe mod
----------------------