Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!sun!pitstop!sundc!seismo!uunet!mcvax!hp4nl!eutrc3!rcbaps
From: rcbaps@eutrc3.UUCP (Pieter Schoenmakers)
Newsgroups: comp.arch
Subject: Re: Not-so RISCy
Message-ID: <493@eutrc3.UUCP>
Date: 22 Feb 89 11:21:47 GMT
References: <732@wpi.WPI.EDU> <11040@tekecs.TEK.COM>
Reply-To: rcbaps@eutrc3.UUCP (Pieter Schoenmakers)
Organization: Eindhoven University of Technology, The Netherlands
Lines: 18

In article <11040@tekecs.TEK.COM> andrew@frip.gwd.tek.com (Andrew Klossner) writes:
>[]
>
>	"Would it be a terrible hardship to only have two data sizes
>	(perhaps character and word) and not allow words to cross word
>	boundaries?"
>
>Data sizes: you need do atomic 8-bit, 16-bit, and 32-bit loads and
>stores in order to deal with all the sorts of device registers you
>might meet.

On the Archimedes (not only the Unix machine), (only 32 and 8 bits (both
aligned) load/store), the I/O bus is 16 bits wide. Reading from I/O space
puts the data in the low 16 bits of the databus; Writing into I/O space
puts the 16 top bits of the databus onto the I/O bus. Both 16 and 8 bit
devices are no problem; all are accessed using 32-bit operations.

---Tiggr