Rich Freeman on 1 Feb 2014 08:19:31 -0800

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Re: [PLUG] Software/Hardware Oscilloscope Logic Analyzer

On Sat, Feb 1, 2014 at 11:07 AM, Eric H. Johnson
<> wrote:
> Like Bhaskar said, but you might want to look at using a parallel port if available over a USB. While there are some people working on it, USB has problems with hard real-time. See: under "Digital I/O". If you need sample rates faster than about 100Khz, then the parallel port is probably not an option either.

Assuming you have the right drivers I could see why a parallel port
might offer better latency (less going on there at the OS level),
though I imagine if you were willing to invest time you could do the
same with USB (disable USB support in the kernel and write your own).

However, I don't get why realtime is a concern here.  If you are
triggering the device with data on the bus and collecting data on the
bus, then as long as the interface to the logic analyzer has enough
bandwidth it really doesn't matter what the latency is.  USB is going
to give you a LOT more bandwidth than a parallel port.

Maybe if you were trying to rig together a logic analyzer that
contained no memory and just fed raw data into the bus latency would
be more of a problem, but I doubt you could ever get such a device to
work on USB unless you made it the only thing on the bus and hacked
the kernel so it really wasn't a USB bus any longer anyway.

Latency really only matters if the PC is going to react to something
that comes in from the analyzer and send something back out.  That is,
unless I'm missing something here...

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