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Re: Ack! Only 4 uarts with FC6!

On Fri, Oct 27, 2006 at 11:07:59PM -0700, Brian Mury wrote:

 > Ok, I'm curious. Is the 4 ports just a default number that is used
 > regardless of whether or not they actually exist?


 > Why aren't the 3rd and
 > 4th ports that are in /dev without the kernel parameter usable


 > (since
 > all it seems to do is tell the kernel how many ports to use)? And why do
 > I need this at all since I didn't need it in FC 1 through 5?

because some people wanted to be able to use 32 port serial cards and the like,
and due to the way the serial core works, you compile it for a maximum number
of uarts, and udev then creates that many /dev entries regardless of whether
they exist or not.  Some people (typically people without cards with lots of ports)
complained when they had all those useless /dev entries, and different people
complained when the default was set so low it wouldn't allow them to use their
'lots of serial ports' devices.

So the boot time switch came to be, which allows you to set it up to a maximum
of what the old compile-time limit is set to.

Serial device port allocation isn't the most straightforward thing, there are
all sorts of funny corner cases.  Another common misconception is that the ttyS
nodes are allocated sequentially, but the IO port that the serial port is mapped
to is what determines which /dev/ttyS node it ends up with.
So having ttyS0, ttyS1, ttyS12, ttyS13 and no other nodes is possible for eg.



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