Serial console ports on systems with no console connected.

Murray Jensen Murray.Jensen at
Wed Jul 10 16:47:28 EST 2002

On Tue, 9 Jul 2002 19:45:19 -0400, Arun Dharankar <ADharankar at ATTBI.Com> writes:
>Also have the serial port speed set at 115200,  I
>dont believe this is buffer overrun issue.

If you want to go faster than about than about 38400, you need to get a
different clock source for your baud rate generators (Tom Rini has a patch
from me to add support for an external clock source for BRGs on the 8260
in linuxppc_2_4_devel). By default, the SCCs and SMCs use a clock source that
won't divide cleanly at the higher baud rates - the error becomes so large
that it simply stops working - which is what you are getting by the looks of it.

Try running the serial ports at 19200 and see if that works. Cheers!

PS: the patch Tom has is trivial - you still need to hack the 8260 uart driver
to use the new code (also trivial), plus your hardware needs an external clock
source (distinctly non-trivial if your board design doesn't include one already
- our hymod board has a 3686400Hz clock source wired appropriately, which allows
up to 230400bps if you use 16x oversampling)

PPS: ppcboot already has support for external BRG clock sources - see
include/config_hymod.h for an example of how to configure it.
Murray Jensen, CSIRO Manufacturing Sci & Tech,         Phone: +61 3 9662 7763
Locked Bag No. 9, Preston, Vic, 3072, Australia.         Fax: +61 3 9662 7853
Internet: Murray.Jensen at

Hymod project:

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