Date: Wed, 25 Jun 2003 13:33:52 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: louie@TransSys.COM Cc: freebsd-hackers@freebsd.org Subject: Re: USB, select/poll for ucom Message-ID: <20030625.133352.08453169.imp@bsdimp.com> In-Reply-To: <200306251858.h5PIwSW8017536@whizzo.transsys.com> References: <E19VCk7-000254-00@cs.huji.ac.il> <20030625.101549.78767546.imp@bsdimp.com> <200306251858.h5PIwSW8017536@whizzo.transsys.com>
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In message: <200306251858.h5PIwSW8017536@whizzo.transsys.com>
"Louis A. Mamakos" <louie@TransSys.COM> writes:
: I think the problem is that the USB hardware doesn't try to read data
: from the peripheral until the user-mode code does a read(2) system
: call. I had this problem with the ugen device. I would guess that
: the ucom/umodem devices could use the tty clist infrastructure as
: the intermediate buffer for data to be stuck into absent the user
: application doing a read.
I thought that ucom does do that. It uses ttypoll as its polling
function, and seems to insert data into the tty structure on an
interrupt basis. That is hidden a little bit by the usb driver
structure. In the middle of ucomopen we call ucomstartread which
posts a read onto the bulk in pipe. This read fires a callback when
it is 'finished' which the processes the data. So I think that maybe
that transfer is never completing.
Warner
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