Messages in this thread | | | Date | Thu, 28 Mar 2002 13:39:43 -0800 | From | David Lawyer <> | Subject | Re: Char devices drivers |
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On Mon, Mar 11, 2002 at 09:59:14AM -0800, Ed Vance wrote: > On Mon, Mar 11, 2002, Henrique Gobbi wrote: > > > > Can anyone explain what is the utility of the callout devices > > in the char drivers ??? > > To further confuse things, most vendors have a "back door" port > configuration mechanism outside of termio(s)/sgtty. For example, Linux has > the setserial command. There is less need for separate callout devices when > the user can set a port to open with the desired flag values.
Setserial doesn't have facilities to set open flags for the ports. The reason cua isn't needed is that the programmer can make a ttyS port look like a cua port by using the O_NONBLOCK or O_NDELAY flags. However the non-blocking flag will not only force an open when CD is asserted, but will make all reads of the port non-blocking. So the programmer can change this if he wants after the port has opened.
So eliminating cua means more work for the programmer but less confusion for users. Overall, it's a good thing since there are many more users than programmers.
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