[coreboot] how to debug without com port

[Martin Roth]

Hi Cheng,
  Without knowing your platform, what you actually have available. and
what your budget is, and where you're stuck, it's hard to say, but
here are some directions you could look:

- If you're making it to an OS but something's wrong, use the CBMEM console.

- EHCI debug could be the best way if you're trying to get a full console:
  https://www.coreboot.org/EHCI_Debug_Port
  https://www.coreboot.org/BBB_screwdriver

- There's also a way to get the console over the PC speaker:
  https://www.coreboot.org/Spkmodem

- If you have a pcie slot, or mpcie slot, you can add a serial port
(Oxford OXPCIe952 is supported)
  https://www.amazon.com/StarTech-com-Profile-Native-Express-PEX1S952LP/dp/B002RYTI7I/ref=sr_1_fkmr0_1
  https://www.amazon.com/StarTech-com-RS232-Express-Serial-MPEX2S952/dp/B003OCRW1Q

- If you have post code leds or a way to read from port 80h, put out a
value and debug it that way.  For more information, you can use
'rolling post codes', where you put out a known value or two, then a
series of values with a delay in between, just in a loop.  "BA BA 99
01 03 7F BA BA 99 01 03 7F ..."

- You can use a rom emulator and the spi console:
  http://www.dediprog.com/pd/spi-flash-solution/em100pro
  https://review.coreboot.org/#/admin/projects/em100

- If you have an LED attached to a GPIO, you can use that to help
figure out how far you're getting, and then answer yes/no type
questions.

- If your board is hanging, you can get some visibility by resetting
the board or powering it down.  This also allows you to debug slowly,
and get answers to yes/no questions.

Note that these are just suggestions and thoughts, and I'd suggest you
investigate some more before buying any additional hardware.  I've
used some, but not all of these methods.  For instance I've never
tested the spkmodem debugging.

Hope this helps.
Martin

On Fri, Jul 15, 2016 at 8:20 AM, cheng yichen <blessyichen at gmail.com> wrote:
> Hi all
>
> Could you please share how to debug without com port out ? Thank you
>
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