So far, I've been using a normal serial console with a device running Linux.
I configured it in two places:
- kernel command line to see kernel messages: console=ttyS0,115200
- /etc/inittab: T0:23:respawn:/sbin/getty -L ttyS0 115200 vt102 (to be 
able to log in)


As to use that serial console I have to open the device, I decided I 
will use a USB-serial console instead. The changes seemed trivial:

- compile all USB/console related stuff in the kernel
- kernel command line to see kernel messages: console=ttyUSB0,115200
- /etc/inittab: T0:23:respawn:/sbin/getty -L ttyUSB0 115200 vt102


However, this doesn't work as I expected:

1) I don't see any "initial" kernel messages on the USB-serial console:

Linux version 2.6.20 ([EMAIL PROTECTED]) (gcc version 4.1.1) #56 PREEMPT Tue 
Feb 20 18:14:38 CET 2007
CPU: XScale-IXP42x Family [690541f1] revision 1 (ARMv5TE), cr=0000397f
Machine: Freecom FSG-3
(...)

I guess that's because kernel didn't initialize USB-subsystem yet?


2) After loading the kernel, my system is set up to wait for 10 seconds 
before continuing and loading the proper "init". 10 seconds should be 
far more than necessary for the system to see all USB devices?
Still, when the system loads, I don't see any kernel messages, system 
loading etc. on ttyUSB0 (I saw these things with console=ttyS0,115200).


3) As soon as the system loads completely, I get a login prompt on 
ttyUSB0 (started by getty). From this point on, I will get kernel 
messages onto ttyUSB0.


Why do I get kernel messages logged on the USB-serial console that late, 
only after the system is fully loaded and after I get a login prompt on 
ttyUSB0?


-- 
Tomasz Chmielewski
http://wpkg.org


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