Messages in this thread | | | From | "Paul Fulghum" <> | Subject | Re: CLOCAL and TIOCMIWAIT | Date | Mon, 26 Feb 2001 19:27:54 -0600 |
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> A customer has just brought to my attention that when you try to use the > TIOCMIWAIT ioctl with our boards and CLOCAL is enabled, you can't check > changes in the DCD signal. He also mentioned that that is possible with > the regular serial ports. > > As I understood, CLOCAL meant disabling DCD sensitivity, so if CLOCAL is > disabled, no changes in DCD will be passed from hardware driver to the > kernel or userspace. The way the serial driver is implemented, this is not > true (i.e. even with CLOCAL enabled, you can still see DCD changes through > the TIOCMIWAIT command). > > My question is: what's the correct interpretation of CLOCAL?? If the > serial driver's interpretation is the correct one, I'll be more than happy > to change the Cyclades' driver to comply with that, I just want to make > sure that this is the expected behavior before I patch the driver. > > Thanks in advance for your comments. > > Later, > Ivan
I believe CLOCAL only governs how DCD is used (or ignored) when opening a port (must be active to complete open) and maintaining a connection (negation signals hangup).
So CLOCAL controls the driver's 'interpretation' of DCD but TIOCMIWAIT monitors the signal transitions without regard to a predefined interpretation (let's the application decide what to do with DCD).
Paul Fulghum paulkf@microgate.com
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