linux-kernel - Re: Real time USB2Serial devices and behaivor

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Message-Id: <200803271248.40519.david-b@pacbell.net>
Date:	Thu, 27 Mar 2008 12:48:40 -0700
From:	David Brownell <david-b@...bell.net>
To:	mgross@...ux.intel.com
Cc:	Greg KH <greg@...ah.com>, lkml <linux-kernel@...r.kernel.org>,
	linux-rt-users@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: Real time USB2Serial devices and behaivor

On Wednesday 26 March 2008, mark gross wrote:
> On Wed, Mar 26, 2008 at 09:27:28AM -0700, Greg KH wrote:
> > Give up and use a "real" serial port, you'll have better luck :)
> 
> but its getting very hard to find real serial ports any more :(

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."  :(

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.

- Dave

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