x11ssh: An attempt to access BMC UART

[3mkusiak]

Welcome

Hi all,
and welcome to the first practical discussion regarding ZarhusBMC! In this thread I'm gonna report my attempt to hardwire into BMC UART. The Idea is I'm gonna give you updates as I go. I want to keep this thread in tinkering spirit, so forgive me for using less formal language. Feel free to join the discussion at any time.

Approach Idea

The approach idea is to hardwire some jumper wires to the mobo for BMC UART access. The x11ssh platform does not have any debug headers nor probe points for this, so I have to "hack in".

What do I know

I've got the following resources:

• Keno Fisher's blog post in which he also hardwired into x11ssh
• X11SSH Gerber files (Thanks to Tim Ansell)
• AST2400 datasheet

We shall see if this is sufficient.

Where am I at

I have freed the mobo out of the casing to solder the wires and realised Keno used only the UART TX pin on the mobo. I on the other hand need to find RX pin/point too. Let's start!

[3mkusiak]

My first idea was to see if I could make up some logical connection by tracing path. I uploaded all the PNGs to Gimp, marked TX probe points Keno has used, and unfortunately I'm missing important PCB layers needed to trace back the connections. It seems I need to open up the files in some dedicated software if I want to have a chance.

[3mkusiak]

I have traced the path and it I found unpopulated pads I can solder to.

Now all that's left is to test this theory I guess.

[miczyg1]

The approach idea is to hardwire some jumper wires to the mobo for BMC UART access. The x11ssh platform does not have any debug headers nor probe points for this, so I have to "hack in".

Didn't you already have BMC UART on the COM1 header?

[3mkusiak]

I did for OpenBMC, but the stock firmware does not have the UART redirection built in. I guess theoretically, I could build the custom u-boot and just flash uboot memory region, but I assume it ain't that easy and would require additional work. This seems like more rock solid method to me.

[miczyg1]

Ohh so you want to access stock BMC firmware via this UART?

[3mkusiak]

Correct.

[3mkusiak]

I soldered the wires. Ain't my proudest job but should work, I verified this by testing connectivity.



Now it's time to assemble the platform, verify if it still runs and test if we've got UART access.

[3mkusiak]

Check this out haha.

It freakin works!

[3mkusiak]

I think that concludes this discussion 😆

[pietrushnic]

Congratulations, this is a remarkable achievement for one day's work. I will push that to social media.