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 [off-list ref] wrote:

Hi sandeep,

On Mon, Jan 9, 2012 at 10:37 PM, sandeep kumar
[off-list ref] wrote:

quoted

Hi All,

I want to know "What is a console?

A console is where the output from printk goes.

quoted

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.

quoted

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.

quoted

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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