[Noisebridge-discuss] cheap USB Analyzer, or signal integrity tools?

[Dr. Jesus]

On Mon, Nov 8, 2010 at 4:05 PM, Michael Prados <mprados at gmail.com> wrote:
> This sounds really cool, since I am taking apart hard drives all the
> time to use the rotary voice coils for my own devious ends, so I'd
> definitely like to hear more about this.  I googled the commands you
> referenced, and am happy to see that there is some documentation for
> the protocol, but am still a little foggy on the higher level layout
> of how this would work.

It's probably easiest to read the datasheet for a HD control ASIC to
find a good block diagram and ToO on the details.

> So, you're saying that there is already a good high bandwidth ADC
> built into a typical hard drive; is this from the read heads?

Yes.

> So the
> idea is that I find a good point to tap into the HD PCB, pipe in my
> USB signals, and they get spit out at me in real time over SATA or
> whichever other HD interface?

No, the ADC output comes out of test points on the logic board.  You
still have to hook up something up to the test points to see the
signal, but now you have all this fancy filtering and decimation
hardware in the disk controller to let you get away with cheaper
digital capture equipment.  If you slow the signal down enough you can
even use your parallel port.

Something I've thought of doing but haven't had a reason to is to use
a vendor's dev package to modify a CDROM drive to do the same thing,
since their controller ASICs also have high speed ADCs connected to
the optoelectronics.  Since DVDs are standardized and don't have a lot
of expensive IP baggage, they are a bit more open my experience.  For
example, the one CDROM controller firmware package I've worked on
professionally was just a rebadged 8051 with no code signatures or any
of that stuff.

> Is it a challenge to keep the hard drive firmware alive once I've
> modified the hardware?

Not really.  Once you read more about how to talk to the diagnostic
monitors on the logic boards you find out it's pretty common to boot
the things without any disk attached in the first place.