[Wlug] Multiple RS232 Com Ports...

Karl Hiramoto karl at hiramoto.org
Mon May 21 09:31:43 EDT 2007


Stephen Daukas wrote:
>
> On 5/21/07, *Karl Hiramoto* <karl at hiramoto.org
> <mailto:karl at hiramoto.org>> wrote:
>
>     Mike Frysinger wrote:
>     > On 5/20/07, Stephen C. Daukas <scd at daukas.com
>     <mailto:scd at daukas.com>> wrote:
>     >
>     >>  I'm wondering if anyone knows how many RS232 devices a
>     "vanilla" Linux
>     >> kernel can manage simultaneously.
>     >>
>     >
>     > there shouldnt be any real limit ... at work, we have ~24
>     USB<->RS232
>     > devices hooked up and we use them all simultaneously to interact
>     with
>     > some hardware
>     >
>     >
>     >> I'd like to be able to have up to 32
>     >> going at once, with data taken from each device written to its
>     own file via
>     >> the standard I/O subsystem.  As far as I know, wouldn't Linux
>     simply fork
>     >> the appropriate number of driver threads to read as many RS232
>     ports as are
>     >> attached with each device's stream written to a "/dev" file?
>     >>
>     >
>     > i'd be more worried about *what* the devices are and *how* you
>     connect
>     > your 32 devices to the machine ... making sure linux has proper
>     device
>     > driver support for it
>     > -mike
>
>
> The *how* is the heart of my question...  If you mean how physically,
> that's a matter of cable and such.
> The driver question is, again, what I was looking into.  If Linux has
> support for multiple RS232s built in
> to one or more generic drivers in a given distro, then we are talking
> about terminal emulation - a.k.a.
> VT100 or ANSI or whatever.  Currently, the lab uses hyperterminal to
> talk with the sondes - the sondes
> are intelligent and provide a tty-based menu for command and control. 
> The devices are known, so the
> *what* isn't really an open question.
>
>     >
>     Yes, there should be no real limit..  At work i have use multile
>     Edgeport/8   http://www.digi.com/products/usb/edgeport.jsp  
>     devices to have may rs-232 ports
>
>
> How do the RS232 FIFO/Interrupts get managed via USB?  In other words,
> each of the RS232s will need to have its "pin-outs" (DB-9) active so
> the sondes believe they are connected in order to avoid their "turning
> off".  Also, is it safe to assume the edgeport has its own drivers?
>
> Regards,
> Steve
Take a look at:
/usr/src/linux/drivers/usb/serial/io_edgeport.c


What do you mean by turning off Sondes?  your sensors?  Your sensors,
may read the rs-232 flow control pins,  If the port is open() then they
probably won't turn off.   What ever program you write will be a lot of
string parsing to send and receive data.

I believe it is the case with all the USB/Serial adapter drivers that
the driver polls over USB the usb/serial converter device.



--
karl.








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