| Looks like the immediate problem is that the kernel doesn't
 | understand/doesn't support the serial console interface?  (Just a
 | guess, really.)

Probably Jornada 5xx serial module is not SCIF (SH3 internal serial interface). 
Jornada 5xx's companion chip(HP F1796 ???) is different from Jornada 6xx.
so you can't access video buffer too.
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UCHIYAMA Yasushi
uch@nop.or.jp