Add support for sending debug output to an I/O port.
It can be used together with QEMU's isa-debugcon driver to log the
coreboot output to a file. The port is configurable and defaults
to 0x402 which has established as the de facto standard. For example,
SeaBIOS+OVMF [1] use that one too.
[1] http://www.linux-kvm.org/page/OVMF
Open Virtual Machine Firmware
Change-Id: I0803f7fc70030242f80003e25c9449c37d71975e
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-on: http://review.coreboot.org/3331
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
038aa29dc2