[coreboot] USB debug cables and emulation

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Thu Jul 3 21:52:15 CEST 2008

On 03.07.2008 21:42, Joseph Smith wrote:
>> -----Original Message-----
>> From: coreboot-bounces at coreboot.org [mailto:coreboot-bounces at coreboot.org]
>> On Behalf Of Peter Stuge
>> Sent: Thursday, July 03, 2008 1:19 PM
>> To: coreboot at coreboot.org
>> Subject: Re: [coreboot] USB debug cables and emulation
>> On Thu, Jul 03, 2008 at 08:45:15AM -0400, Joseph Smith wrote:
>>> I'm thinking a Serial->USB debugger is the way to go
>> Ok. Keep in mind that the serial port will probably not be able to
>> handle full speed data from the debugged target. I'm not sure what
>> the transfer overhead is, but I expect the debug device to be able
>> to shuffle quite a bit of data even though each transfer is only 8
>> bytes max.
>>> to keep the costs down
>> As Tom pointed out, this is not a good argument. Serial will only be
>> simpler to implement, not lower cost to any degree that matters.
>>> Any suggestions, questions, comments?
>> You might want to look into the speed thing. I believe the best way
>> to do so is to run tests on the NET20DC.
>> On Thu, Jul 03, 2008 at 12:28:47PM -0400, Joseph Smith wrote:
>>> $20 Dollars for a PCB??? I am going to use a generic PCB you can
>>> pick up at radio shack for 2 dollars.
>> That will not work. There are no standalone USB 2 high-speed
>> function controllers that are usable with those PCBs. You will
>> have to design a PCB, or buy a devkit.
>>> This is more for educational, learning, and teaching purposes.
>>> Everything is not about money you know (or not) :-(
>> Manufacturing electronics is VERY expensive, and I think the concern
>> is that you will either be spending ridiculous $$ or be forced to
>> shut down the project before finish, and that either would be a high
>> price for whatever knowledge has been gained.
>> USB Debug Devices aren't the best target for learning USB in general
>> because the devices need to do some tricks here and there, and thus
>> require high end function controllers that can perform.

As luck has it, the USB chips used in the NET20DC are also present in
other devices.

> So everyone is just telling me I should give up??? 

Well, I think it would be really cool to have an affordable USB debug
device. Unfortunately, I am not so skilled when it comes to designing
hardware, so I won't be able to help.
Together with shipping, the NET20DC is >$140 anywhere in Europe. That's
pretty much outside my budget.

> I wonder how many times OLPC herd that???
> Ok then I will just give up and go buy a Net20DC :-(

If you can get schematics and photos and a dump of the ROM of a NET20DC,
you should be able to find out rather quickly whether this is doable. In
theory, having a Geode/CS5536 board should enable you to abuse one of
the USB host ports as device port and create USB debug functionality
purely in software. No idea whether the hardware is that flexible, though.



More information about the coreboot mailing list