What is a console? and Why it is always associated with UART?

[Peter Teoh]

Hi Dave And Sandeep,

Hope I can contribute and sorry for the interruption of conversation :-(.

On Tue, Jan 10, 2012 at 2:59 PM, Dave Hylands <dhylands at gmail.com> wrote:

> Hi sandeep,
>
> On Mon, Jan 9, 2012 at 10:37 PM, sandeep kumar
> <coolsandyforyou at gmail.com> wrote:
> > Hi All,
> >
> > I want to know "What is a console?
>
> A console is where the output from printk goes.
>
> > and Why it is always associated with
> > UART?"
>


Yes, console is output and UART is the hardware device input port.....it
can be implemented hardware wise by many different devices, but all of them
will speak the UART protocol:

http://en.wikipedia.org/wiki/Universal_asynchronous_receiver/transmitter

and the hardware devices' source codes are in
drivers/tty/serial/8250_xxxxx.c for examples (xxxx for different devices).



>
> While console's may often be associated with a UART (typical for
> embedded systems) there is no need or requirement for them to be
> associated with a console. You can regitser a console to send the
> output wherever you like.
>
> > What is a serial console??
>
> A serial console is a console driver (registered via register_console)
> which sends the output to a serial port, typically also allowing the
> serial port to be used as a tty interface.
>
> > Can there be a USB console??
>
> Sure. I don't know if a driver for this exists yet, but if it doesn't
> you can always write one.
>
>
According to the diagram of the book "Essential Linux Device Drivers" page
175, both the output of serial_core.c and usb-serial.c (which implements
the serial signals coming in from the USB interface) are directed to
n_tty.c (which essentially goes to the serial console output).   So answer
is NO, current architecture has the tty console linked to both UART and
USB-Serial interface.   (a FTDI software driver
drivers/usb/serial/ftdi_sio.c is needed to convert the USB signal back to
the serial packets structure).


> There is already something called a netconsole (see
> Documentation/networking/netconsole.txt). This is an example of a
> console which isn't associated with a serial port.
>
> There is also a framebuffer console (See Documentation/fb/fbcon.txt)
>
> --
> Dave Hylands
> Shuswap, BC, Canada
> http://www.davehylands.com
>
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>

Happy Hacking.....


-- 
Regards,
Peter Teoh
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