Console and outputs

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Coreboot has various possible consoles:

Output name direction (from the target coreboot machine point of view) Requirements software compatibility (compatibility with software loaded after coreboot, like OS payloads etc...)
Serial console

(sends coreboot logs over the serial port)

  • input
  • output
  • An internal(not USB) serial port:
    • it can on the mainboard
    • it can also be a PCIe OXPCIe952 card with the 0x1415 and 0xc158 vendor and device ID (respectively).
    • USB serial ports are not supported by coreboot yet.
  • seabios
  • grub as a payload
  • grub running after seabios
  • libpayload
  • linux kernel (loaded after the payload)
  • most GNU/Linux init systems(sysvinit, systemd, upstart etc...)
Console Over EHCI debug port

(sends coreboot logs over the usb debug port)

  • input?
  • output
  • An USB debug port supported by coreboot.
  • To find on which usb connector it goes.
  • grub
  • linux kernel in its early initialisation (I'm not sure that it can be kept afterward, because, after the early initialisation, by default it tries to initialise the USB port normally)
Console trough spkmodem

(sends coreboot logs over the sound card)

  • output only
  • A working "beep" sound card at boot.
  • On some laptops it's necessary to tell the embedded controller to enable sound output to get it working.

For writting to it from the coreboot target computer:

  • coreboot's console
  • grub's console

For reading it from a remote computer:

  • coreboot's/grub's spkmodem_recv uttilty (same uttility, but it's available in both git repositories)
Network console

(sends coreboot logs over the network)

  • output
  • probably no input
  • A ne2k compatible ethernet card on the coreboot target system.
  • A network between the coreboot computer and the computer receiving the logs.

For sending the logs:

  • the linux kernel

For receiving the logs:

  • nc and similar networking uttilities.
Cbmem console

(Ram buffer, like dmesg)

  • output only for coreboot.
  • input/output for grub.
  • It requires the computer to be booted to retrive the logs.
  • A coreboot device that supports cbmem: not all devices supports it in coreboot.

For writting to the buffer which is in the coreboot target computer:

  • coreboot console output
  • grub console output
  • seabios

For reading the buffer on the coreboot target computer, after coreboot booted:

  • grub with the cbmemc command
  • coreboot's userspace cbmem -c uttility

Other output: