[Techtalk] ttyS1: LSR safety check engaged!

Robyn rmanning at iinet.net.au
Sun Sep 11 01:48:22 EST 2005

On Fri, 2005-09-09 at 20:51 -0700, Carla Schroder wrote:
> On Wednesday 07 September 2005 8:56 pm, agoats wrote:
> > > Simple question- wot the heck does 'ttyS1: LSR safety check engaged!'
> > > mean? It's dmesg output. I have Googled, and found only other puzzled
> > > souls.
> > >
> >
> > This one's obscure enough I'm going to jump in early... no offense!
> >
> > All of the LSR instructions are buried in the serial driver source code
> > for the kernel source.
> >
> > /usr/src/linux/drivers/char/serial.c
> Thanks, I don't mind digging through obsure docs when I'm in the mood. :)
> The amusing bit is on this particular PC there is only one serial port & UART, 
> on ttyS0. This is what setserial shows:
> $ setserial -g /dev/ttyS[0123]
> /dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
> /dev/ttyS1: No such device
> /dev/ttyS2, UART: unknown, Port: 0x03e8, IRQ: 4
> /dev/ttyS3, UART: unknown, Port: 0x02e8, IRQ: 3
In times previous internal modems or anything internal that had it's own serial
port had to have the corresponding port disabled on the motherboard.

ttyS0 and ttyS2 share irq 4, ttyS1 and ttyS3 share irq 3 yet your
setserial listing shows ttyS1 No such device and ttyS3 has UART: unknown
etc. The output on ttyS3 is what you get when the port doesn't exist.

Some motherboards let you plug in a second serial port to the board with
it mounted on a slot cover. This port if available in the cmos is often
either an Infrared port or a serial port.


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