[coreboot] USB debug cables and emulation

Joseph Smith joe at settoplinux.org
Thu Jul 3 18:28:47 CEST 2008

> -----Original Message-----
> From: coreboot-bounces at coreboot.org [mailto:coreboot-bounces at coreboot.org]
> On Behalf Of Tom Sylla
> Sent: Thursday, July 03, 2008 10:56 AM
> To: Joseph Smith
> Cc: stepan at coresystems.de; Ken.Fuchs at bench.com; c-
> d.hailfinger.devel.2006 at gmx.net; coreboot at coreboot.org
> Subject: Re: [coreboot] USB debug cables and emulation
> 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?

I guess you don't get it. I am not doing it to mass produce and sell at a
lower cost. I don't really care about any kind of profit. I'm simply doing
it for a "HOWTO build your own USB 2.0 Debugger For Around 20 Dollars". $20
Dollars for a PCB??? I am going to use a generic PCB you can pick up at
radio shack for 2 dollars. If I have to get some of the components at a
larger volume to get a cheaper price and re-sell them to interested parties
so they get a cheaper price I will. This is more for educational, learning,
and teaching purposes. Everything is not about money you know (or not) :-(

Joseph Smith

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