[Thumbgps-devel] USB handshake signals and Linux

[Dave Taht]

On Wed, Mar 14, 2012 at 11:42 AM, Eric S. Raymond <esr at thyrsus.com> wrote:
> Patrick Maupin <pmaupin at gmail.com>:
>> The FTDI devices have a latency timer that allows you to control this
>> somewhat.
>

In a private chat late last night andrew mentioned that the ftdi devices
were extensively reprogrammable, in that they came as a usb device
but were really, underneath, just a bunch of gpios...

> I found a couple of hits on the search "PL2303 latency timer" that
> implies it has one too.  But I doubt the value of the latency timer
> will be relevant for handshake-line notifications; see below.
>
>>       But even better, if we're going to use the PPS signal, they
>> essentially guarantee that they will send ASAP on modem control signal
>> change.  We might need to characterize "ASAP" but I would hope that it
>> doesn't vary too much.
>
> Probably not.  Trying to buffer a handshake state change doesn't make
> any sense. I'm not surprised that the FTDI gives them realtime
> priority and I *will* be surprised if the PL2303 (or any other
> adapter) doesn't do likewise.
> --
>                <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
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Dave Täht
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