[coreboot] $7 cheap FT232H board as EHCI debug dongle for coreboot - would it work?

[Kyösti Mälkki]

Hi Mike

On Sat, Mar 3, 2018 at 3:27 PM, Mike Banon <mikebdp2 at gmail.com> wrote:
> Good day! I am looking for the dirt cheap EHCI debug dongle. Initially
> I found these instructions for FX2LP -
> https://www.coreboot.org/DIY_EHCI_debug_dongle - but they require a
> lot of manual soldering/mods which depend on your boards revision and
> I am not sure if the currently produced boards are 100% compatible
> with the wiki instructions

PCBs indeed have some variations. I pretty much abandoned all efforts
with FX2LP. However, some people were able to emulate the discontinued
net20dc dongle product with the FX2LP approach, to the level it was
operational with proprietary windows kernel debugger.

>
> But then I noticed a coreboot has USBDEBUG_DONGLE_FTDI_FT232H option:
> " Use this with FT232H usb-to-uart. Configuration is hard-coded to use
> 8n1, no flow control "
>
> Kyösti Mälkki tested it " with gizmosphere/gizmo1 Explorer add-on
> board, which exposes the following device:
>    0x0403 Future Technology Devices International, Ltd
>    0x6014 FT232H Single HS USB-UART/FIFO IC "
> but gizmo1 is expensive and I am not a fan of the single board
> computers (SBCs) : they all require the binary blobs which could
> contain the scary backdoors
>

Just forget all the talk about gizmo1, it was just the way I was able
to test it i.e. I had the hardware at hand.

> However, there are $7 cheap FT232H boards with USB available at AliExpress:
>
> https://www.aliexpress.com/item/NEW-CJMCU-FT232H-Multifunction-High-Speed-USB-to-JTAG-UART-FIFO-SPI-I2C-Module/32818305310.html
>
> I plan to get a couple of these boards, connect them to each other
> with 1P 2.54mm wires, plug the 1st board into master PC
> (coreboot-PC-under-debug) USB 2.0 port and the 2nd board into slave PC
> (another coreboot PC which will be logging the debug info)
>
> Please tell me: could this setup work in theory, or there are obvious
> shortcomings that could prevent it from working?
>

Sounds good with three wires, cross RX&TX, add GND. Only the 1st board
(DUT) has to be FT232H, 2nd can be regular uart-to-usb like FT232R or
PL2103(?), This FT232H board also does the job of external SPI flash
recovery with flashrom.

And.. kudos for Nico H for the initial FT232H init sequence code.

Kyösti