Serial console

Supported Serial Ports

SuperI/O with integrated UARTs

coreboot supports a variety of SuperI/O chips with UART functionality. If your mainboard has a serial port built-in, you can use it with no or minimal changes.

PCIe/Mini PCIe based serial cards

Experimental coreboot and libpayload support is available for the StarTech MPEX2S952 card. Those cards are available at Amazon for around 60 USD. In order to use the card for romstage debugging, minimal setup of the PCIe bridge and the MPEX2S952 have to be added to romstage.c, otherwise the card is only available after the resource allocator has been running.

USB to Serial Converters

USB to serial converters are not supported by coreboot at this time.

Enabling Serial Console

In order to get serial console output from various components of your system special options may be needed. This page tries to give a short description of how to use these options.

coreboot

In coreboot you have to set up serial console support during configuration. Enable Console--> Serial port console output. You will be able to choose the UART and baud rate settings in the same menu.

FILO

FILO picks up coreboot's serial console configuration, if compiled with serial console support.

GRUB legacy

In your boot/grub/menu.lst add the following:

serial --unit=0 --speed=115200
terminal --timeout=15 serial console

Change --unit=0 to --unit=1 for the second serial port (COM2).

GRUB2

The usual way to get serial is to have the following in /etc/default/grub:

GRUB_TERMINAL_INPUT="console serial"
GRUB_TERMINAL_OUTPUT="console serial"
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"

But that depend on having console(and so graphics) working(if console fails serial isn't tried), so adding the following to the end of /etc/grub.d/40_custom

serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1
terminal_input --append  serial
terminal_output --append serial
set timeout=1
play 480 440 1

Then regenrate the grub config: For debian, ubuntu, trisquel:

sudo update-grub2

for arch, parabola:

grub-mkconfig -o /boot/grub/grub.cfg

Linux kernel command line

Add

console=ttyS0,115200 console=tty0

to send debug output to both the serial console on COM1 and to VGA.

if you use grub2 you can add it to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub

Then regenrate the grub config: For debian, ubuntu, trisquel:

sudo update-grub2

for arch, parabola:

grub-mkconfig -o /boot/grub/grub.cfg

Linux login prompt

In /etc/inittab add/enable a line like this:

T0:23:respawn:/sbin/getty -L ttyS0 115200 vt100

Change ttyS0 to ttyS1 for COM2.

ubuntu, trisquel based

Create a file called /etc/init/ttyS0.conf containing the following:

# ttyS0 - getty
#
# This service maintains a getty on ttyS0 from the point the system is
# started until it is shut down again.

start on stopped rc or RUNLEVEL=[2345]
stop on runlevel [!2345]

respawn
exec /sbin/getty -L 115200 ttyS0 vt102

Then do

sudo start ttyS0

Hardware pinouts

de9

Pin	Function
1	DCD
2	RX
3	TX
4	DTR
5	GND
6	DSR
7	RTS
8	CTS
9	RI

standard 10 pins PC mainboard connector

Pin	Function
1	DCD
2
3
4
5
6
7
8
9
10	NC

non-standard "intel" 10 pins PC mainboard connector

Pin	Function
1	DCD
2
3
4
5
6
7
8
9
10	NC

Notes

While serial is the most supported console(support in coreboot,seabios,serialice,ipxe,memtest etc...) it's not available on every hardware anymore, some recent devices like the Lenovo X201 or the Chromebook pixel lack a serial port...

See also

Console_and_outputs

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