Re: Real time USB2Serial devices and behaivor

Lennart Sorensen
2008-03-27T21:00:50Z

On Thu, Mar 27, 2008 at 12:48:40PM -0700, David Brownell wrote:
> I happened across this the other day, and saved the URL since
> the price was relatively sane ... $15 vs the $60 I saw at
> another site, although ISTR Fry's used to have them at $5:
>
> http://www.wrighthobbies.net/catalog/index.php?cPath=47
>
> Yeah, I know. "It's getting very hard to find real PCI slots
> any more." :(

Well digi (www.digi.com) makes some nice PCI serial cards, that work
with the jsm driver. Not sure how many models are supported, but
certainly I have used the 2 port card with DE-9 connectors.

A little bit of patching will make the jsm driver run any exar
17[CD]15[248] based card, like the ones we use on the routers I work on.
The digi cards use a rebranded exar chip with a different PCI id. Much
better than using the 8250 driver to run the exar's in PCI 16550A mode,
although it does work.

They have PCIe cards too although I have no idea if they use the same
interface or not (it would make sense to do so on the part of exar
though).

> It seems like some companies (notably *cough* Intel) are
> on a little jihad to get rid of serial ports...
>
> I'd think that in a controlled environment (fixed set of
> USB connections) USB should be able to meet fairly chosen
> "real time" latency ceilings. The stack probably needs a
> few semantic updates to make it happen -- e.g. URB completions
> are issued in_irq() -- but it shouldn't be insurmountable.

--
Len Sorensen