[Gllug] set serial port irq

[Jack Richards]

You wont get any data flow if the DTR lines are required ( sometimes this is 
impossible to disable through software because of the way the serial port 
hardwrae is implemented - I've had this on a number of occasions with HP and 
Sun Hardware for example )

DTR is used to control the hardware flow on the SERIAL FIFO buffers in hardware

A simple 9.99 line analiser solves many of these problems straight off.  My 
gut feeling is that the cable you are using is not using all the lines and may 
actually be a 3 or 5 pin implementation.  ( tx rx gnd or tx rx cts rts gnd )

I believe that there is a DTR=always on flag somewhere in the serial setup 
programs though for the life of me I can't remember where ( might not even be 
in Linux :-} ) 

Quoting Ben Fitzgerald <ben_m_f at yahoo.co.uk>:

> On Mon, Apr 19, 2004 at 04:19:37PM +0100, Jack Richards wrote:
> > This is where a faker box really comes in handy.
> > 
> > Sounds like you may have a DTR related issue
> 
> You mean this in /var/log/mgetty.log.ttyS0:
> 
> 04/19 17:01:04 yS0  WARNING: DSR is off - modem turned off or bad cable?
> 04/19 17:01:04 yS0  lowering DTR to reset Modem
> 
> > Best thinng to do is to turn off your iniitab getty for this serial port
> and 
> > test the serial connectivity at a lower level.
> > 
> > Try running cat > /dev/ttySX on the reciever machine and echo "hello" 
> > >> /dev/ttySY on the sending machine
> 
> Did you mean cat /dev/ttyS0? I tried both just in case.
> 
> Tried that, and the echo hangs (and hangs...). It does complete after
> 60 seconds or so but nothing has arrived on the other box.
> 
> I guess it must be having trouble initiating the connection and so
> keeps trying but can't get to send characters across.
> 
> > Check to see if your getting stuff.  Use stty -F /dev/ttySX and set ospeed,
> 
> > ispeed to the correct values first and use setserial and the uart flag to
> set 
> > the UART to 16550A.
> 
> receiver# stty -F /dev/ttyS0 ospeed 115200 && stty -F /dev/ttyS0 ispeed
> 115200
> sender# stty -F /dev/ttyS0 ospeed 115200 && stty -F /dev/ttyS0 ispeed 115200
> 
> tried to echo hello across again but still no joy :(
> 
> > if you are not getting data after this, then consider that your cable is
> not 
> > xover ( pin 2 to 3 3 to 2 7 to 7 etc ) or that your flow control is not
> right.
> 
> perhaps pcworld on the way home...
> 
> Ben
> -- 
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Jack Richards

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