From owner-freebsd-hackers Thu Nov 13 21:32:56 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id VAA26757 for hackers-outgoing; Thu, 13 Nov 1997 21:32:56 -0800 (PST) (envelope-from owner-freebsd-hackers) Received: from out1.ibm.net (out1.ibm.net [165.87.194.252]) by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id VAA26752 for ; Thu, 13 Nov 1997 21:32:54 -0800 (PST) (envelope-from mouth@ibm.net) Received: from slip129-37-53-114.ca.us.ibm.net (slip129-37-53-114.ca.us.ibm.net [129.37.53.114]) by out1.ibm.net (8.8.5/8.6.9) with SMTP id FAA85668; Fri, 14 Nov 1997 05:32:37 GMT From: mouth@ibm.net (John Kelly) To: Bruce Evans Cc: hackers@FreeBSD.ORG Subject: Re: Status of 650 UART support Date: Fri, 14 Nov 1997 06:33:52 GMT Message-ID: <346ced6b.754999@smtp-gw01.ny.us.ibm.net> References: <199711140301.OAA11983@godzilla.zeta.org.au> In-Reply-To: <199711140301.OAA11983@godzilla.zeta.org.au> X-Mailer: Forte Agent 1.01/16.397 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by hub.freebsd.org id VAA26753 Sender: owner-freebsd-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk On Fri, 14 Nov 1997 14:01:41 +1100, Bruce Evans wrote: >>Why not start from scratch and develop siov2.c which uses elastic >>buffers, 650 polled vs. interrupt mode switching, yada, yada, yada. > >High costs/benefits. It can't be made more than about 10% faster in >that way on a reasonably fast CPU, since most of the overheads are >for waiting for the ISA bus. I recall reading that 16-bit ISA I/O is faster, per byte, than 8-bit ISA I/O. I wonder how much better you could do with a card which transferred two bytes at once on the 16-bit bus. You would just need some kind of buffer between the UARTs and the bus. Maybe even shared memory ... oh well I guess I could buy a Cyclades card or such rather than go to all that trouble. John