[coreboot] USB debug cables and emulation

Tom Sylla tsylla at gmail.com
Thu Jul 3 16:55:45 CEST 2008

On Thu, Jul 3, 2008 at 8:45 AM, Joseph Smith <joe at settoplinux.org> wrote:
> Well it looks like in the pdf presentation above they have a Serial->USB
> debugger. It looks like a development board though because there are a
> bunch of unnecessary stuff on it. I'm thinking a Serial->USB debugger is
> the way to go to keep the costs down, and it gives the terminal PC (serial
> end) more flexability. If one wanted to have it USB on both ends they could
> always use a USB->Serial adapter for the terminal PC (serial end). Also,
> this way there would be no need for any kind of a special driver for
> windows/linux, it would just show up as a serial communications device. Any
> suggestions, questions, comments?

I think I am still a bit confused about your goal.

A Net20DC is ~$90 right now.

You aren't going to be able to take some off-the-shelf USB-Serial
adapter and make it into a debug device. Those adapters use
fixed-function USB-Serial ICs that are cheap and small. You can't
re-program the firmware to make them into debug devices. If you buy a
development kit with an appropriate IC and allows you to develop the
firmware, you will easily be at $90 or above.

To make a replacement, you need:
Net2272 (or equivalent, Cypress, etc) ~$10
"host side" interface chip ~$5 ($5 for serial, USB would be ~10 instead)
Connectors, SEEP, passives, etc $10
PCB $20

So, $50 *cost* (and the above numbers are very best-case). Then you
need to assemble and test your board, develop the firmware for the USB
debug Device, and possibly the firmware for the host-side interface.
(Please don't try and argue less than $20 for a PCB, for your
quantities, that is what it will be)

Even if you consider all of your time "free", you still are comparing
$50 to $90.

If you could sell a USB debug cable for $20, it would make sense. If
the Net20DC was $200, it would make sense. Otherwise, I am not so
sure. Am I missing something?

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