Path: utzoo!attcan!uunet!husc6!mailrus!ames!pasteur!ucbvax!PURDUE.EDU!comer
From: comer@PURDUE.EDU (Douglas Comer)
Newsgroups: comp.os.xinu
Subject: Re:  putting a char to console (SUN Xinu)
Message-ID: <8805231449.AA09097@merlin.cs.purdue.edu>
Date: 23 May 88 14:49:57 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 21

Mike,

   All hardware is different.  In the ideal world, we want to 
separate upper and lower halves so the upper half deals only
with user prcoesses and the lower half deals only with hardware.
However, on the SUN, the hardware does not generate an interrupt
when enabled, so the upper half must take more explicit action
to start the device.  In fact, the SUN may not use the real
tty hardware at all -- it may direct output to the bit-mapped
screen (in which case there is no interrupt...).

   As for bypassing the the device switch table, I think you
overlooked something.  Even in the early versions of Xinu, the
iint and oint entries in the device switch table were consulted
at system startup and then stored in the intmap table that
gets used by the interrupt dispatcher.  The reason is simple --
it's too inefficient to index the device switch table on every
interrupt.

Cheers,
Doug