Add a Serial port to the LS-WSXL (LS Mini v2)

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Revision as of 16:31, 4 January 2017 by Pabr (Talk | contribs) (Created page with "{{Articles|Hardware|LS-WSGL/R1}} =Hardware= Image:LS_WSXL-serial.jpg The serial port is CN6, near the LEDs on the front of the device. Traces for RX and TX are interru...")

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Hardware

LS WSXL-serial.jpg

The serial port is CN6, near the LEDs on the front of the device.

Traces for RX and TX are interrupted under IC7, but they can be bridged on the other side of the PCB (see http://forum.buffalo.nas-central.org/viewtopic.php?t=23905 ).

The pad layout under IC7 suggests that two more traces are intended to be connected, but it looks like this would bridge 5V from the power jack with 3.3V (probably not a good idea).

u-boot

u-boot does not offer a serial console, even after "nvram -c set stdout serial". TBD: Check other firmware versions.

Linux

With linux-2.6.22.18-88f6281 the only boot message is from the kernel decompressor:

--- CONFIG_BUFFALO_PLATFORM --- Uncompressing Linux..[...].. done, booting the kernel.

Afterward the kernel says "Warning: unable to open an initial console." and /dev/ttyS0 does not work. TBD: Check other firmware versions.

Kirkwood bootstrap ROM

Marvell Kirkwood processors apparently have ROM code that checks for a special trigger on the serial port before passing control to u-boot.

  • Run

stty -F /dev/ttyUSB0 115200 (while true; do echo -ne '\xdd\x11\x22\x33\x44\x55\x66\x77'; sleep 0.001; done) > /dev/ttyUSB0

  • Apply power. The blue LEDs will not flash as usual; this confirms that the boot process has been interrupted.
  • A terminal emulator will display "Bootstrap 1.21>"
At this point it should be possible to upload a freshly-compiled u-boot (not tested yet).