Re: [Gumstix-users] Open bidirectional ttyS0

[Craig H. <cr...@gu...>]

On Oct 10, 2007, at 7:31 PM, Dave Hylands wrote:

> HI Scott,
>
>> I have an avionics box that sends constant binary data.  When I  
>> hooked the
>> avionics box up to HyperTerminal, I can see this data stream.  On the
>> gumstix, I want to connect this device to /dev/ttyS0 but I noticed  
>> that
>> getty was taking control of this port trying to produce a login  
>> prompt.
>> Under /etc/inittab I modified the getty to release control of /dev/ 
>> ttyS0 and
>> now I have an open bidirectional ttyS0.  I proved it by connecting
>> HyperTerminal to /dev/ttyS0 on the gumstix and I could type  
>> characters from
>> the HyperTerminal onto the gumstix and visa versa.  When I hooked  
>> up the
>> avionics box to the gumstix, and ran cat /dev/ttyS0 nothing shows  
>> up on my
>> screen.  I even tried tail /dev/ttyS0 and still nothing came cross  
>> the port.
>>  Shouldn't I see junk coming onto the gumstix from the avionics  
>> box?  Anyone
>> have any suggestions?
>
> cat won't setup the baud rate or other serial attributes. I like to
> use a program I wrote called sertest. It  opens the serial in raw
> mode, and allows bidirectional communication with the serial port
> (whereas cat is unidirectional).
>
> You can find sertest over here:
> <http://docswiki.gumstix.com/Sample_code/C/Serial>

I like to use socat for this kind of stuff, because it allows you to  
specify all the termios stuff on the command line, and lets you do  
neat tricks like pipe between the serial port and a raw TCP socket, eg:

socat open:/dev/ttyS0,raw,clocal,B115200 stdio

will connect a binary serial connection to a local device with no  
flow control at 115200bps to your current stdin/stdout, or

socat open:/dev/ttyS0,raw,clocal,B115200 tcp4:somehost:1234

will connect the serial port to a TCP server running on somehost on  
port 1234, or even

socat open:/dev/ttyS0,raw,clocal,B115200 tcp4-listen:1234

will open a TCP server to listen for inbound connections on port 1234  
and then will connect those up to the serial port.  Or if you enable  
openssl in socat, you can even use modes like openssl-listen which  
will automagically encrypt the TCP connection for you.  socat is  
basically like netcat on steroids.

C