Re: USB, select/poll for ucom

From: M. Warner Losh (imp_at_bsdimp.com)
Date: 06/25/03

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    Date: Wed, 25 Jun 2003 13:33:52 -0600 (MDT)
To: louie@TransSys.COM

    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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