[argyllcms] Re: ubuntu-10.10-desktop-amd64: dispcal -D5 -? hangs

Hal V. Engel wrote:


This may work for some situations but it is far from fool proof.  One example.
I have a time keeping serial GPS connected to my system (Motorola Oncore UT+)
that is used by ntp for precise time keeping (<  +- 1 microsecond after it has
stabilized).  Nothing related to this including the kernel module that creates
the interrupt from the one second pulse that marks the epoch or ntp creates a
lock of any kind.  Messing with this serial port could cause a time keeping
failure on systems like mine.   This type of set up is not common since Pulse
Per Second (PPS) support was only added to the linux kernel recently (2.6.32 -
FreeBSD has had this for several years now and is the reference
implementation) but I suspect that PPS support is only one example of systems
that do not create locks when using a serial port.


Hi Hal,
        this is an unfortunate example. I notice that the setserial
program gets more information about the serial ports by opening them
O_NONBLOCK and then doing an ioctl TIOCGSERIAL. So it would seem
that anyone doing a "setserial -g /dev/ttyS*" will upset
your device. I notice that similar information is
in /proc/tty/driver/serial, but the software would need
elevated privileges to read this file. In contrast, attempting
to open the devices ends up listing devices that could be
opened with the current credentials.

Graeme Gill.

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