On 12/31/06, Jack Carroll <[EMAIL PROTECTED]> wrote:
Tapping a PCIe signal should be doable, but it would take some
serious engineering at the electrical level. What I'd try is to tap the
transmission line with a 3-arm T attenuator, with most of the power passing
straight through, and a greatly attenuated signal coming out the side arm.
Then terminate the side arm, and amplify back to standard logic levels for
compatibility with a logic analyzer. The tap adapter would have to be
implemented as a microwave PC board, with connectors to plug between the
device and the cable.
I envision having 1x and 16x "extender" sockets. The extender plugs
into the mobo, and the device being debugged (let's call it the
"subject" or "agent" or "object" or "patient," perhaps) is plugged
into the extender. We can then use what you're describing as a way to
get at the signals. PCIe, with its differential signalling and
self-timing should handle a reasonable amount of trace lengthening.
Reflections are what's going to kill us. You can get reflections from
tees, as well as from impedance mismatched connectors, and a number of
other things that I don't know as much as you do about.
--
Timothy Miller
http://www.cse.ohio-state.edu/~millerti
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