[coreboot] Re: How to debug open-source AGESA with serial console?

[Clay Daniels]

Paul, you are probably way ahead of this, but I found something pre-AGESA
from 2003 that says:

"Unlike minicomputer systems, the IBM PC was not designed to use a serial
console. This has two consequences.

Firstly, Power On Self-Test messages and Basic Input/Output System (BIOS)
messages are sent to the screen and received from the keyboard. This makes
it difficult to use the serial port to reconfigure the BIOS and impossible
to see Power On Self-Test errors.

An increasing number of manufacturers of rackable *server* equipment are
altering their BIOSs to optionally use the RS-232 port for BIOS
configuration and test messages. If you are buying a machine specifically
for use with serial console you should seek this feature. If you have an
existing machine that definitely requires access to the BIOS from the
serial port then there are hardware solutions such as PC Weasel 2000
http://www.realweasel.com/.

Secondly, the RS-232 port on the IBM PC is designed for connecting to a
modem. Thus a null modem cable is needed when connecting the PC's serial
port to a terminal."

https://tldp.org/HOWTO/Remote-Serial-Console-HOWTO/intro-why.html

Clay

On Thu, Oct 15, 2020 at 3:54 AM Paul Menzel  wrote:
> Dear coreboot folks,
>
> To get PCI bridge 0:15.2 enabled for the network device on the Asus
> F2A85-M PRO, I want to debug the PCIe General Purpose Ports lane
> configuration of the FCH.
>
> I’d like to print some variables in
>  src/vendorcode/amd/agesa/f15tn/Proc/Fch/Pcie/GppPortInit.c
>
> over the serial console. It looks like
>  #include <console/console.h>
>
> and `printk(BIOS_DEBUG, …)` compiles, but the messages are not sent over
> serial console. Is that expected?
>
> Do I need to use AGESA’s Integrated Debug Services (IDS) [1], and enable
> the console in `src/mainboard/asus/f2a85-m/OptionsIds.h`?
>
> Kind regards,
>
> Paul
>
> [1]:
>
> https://www.coreboot.org/images/3/36/AGESA_Interface_Spec_for_Arch_2008_v3.0...
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