Difference between revisions of "Serial console"

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kernel running on a board.  Therefore, it is very common to boot a kernel using a "serial console".
 
kernel running on a board.  Therefore, it is very common to boot a kernel using a "serial console".
 
That is, the console messages, and the ability to log in to the newly running kernel are provided
 
That is, the console messages, and the ability to log in to the newly running kernel are provided
via a serial connection to the development board.
+
via a serial connection to the development board (rather than via a VGA screen and keyboard combination,
 +
which is the default for desktop versions of Linux).
  
 
To use a serial console, you must have a kernel with the necessary serial port driver configured
 
To use a serial console, you must have a kernel with the necessary serial port driver configured

Revision as of 22:49, 18 September 2007

Often, embedded development boards and products do not have normal displays that are available for kernel console messages. This is especially true during the early stages of getting a new kernel running on a board. Therefore, it is very common to boot a kernel using a "serial console". That is, the console messages, and the ability to log in to the newly running kernel are provided via a serial connection to the development board (rather than via a VGA screen and keyboard combination, which is the default for desktop versions of Linux).

To use a serial console, you must have a kernel with the necessary serial port driver configured in, and you must boot the kernel and specify to use a serial console on boot.

The kernel configuration options to support this are (usually):

  • CONFIG_SERIAL_8250=y
    • other serial ports are also supported, but this is the most common serial UART hardware
  • CONFIG_SERIAL_8250_CONSOLE=y

An example kernel command line option to specify the serial console (and it's settings) are:

  • console=ttyS0,115200n8

This option tells the kernel to use ttyS0 (the first serial port), with settings of speed=115200 cps, no stop bits and 8 data bits. The serial ports of the host and the target should be configured to match in terms of the speed, stop bits and data bits. Minicom is a common serial communications program used on host machines for accessing the console from the host.