Date: Fri, 14 Nov 1997 06:33:52 GMT From: mouth@ibm.net (John Kelly) To: Bruce Evans <bde@zeta.org.au> Cc: hackers@FreeBSD.ORG Subject: Re: Status of 650 UART support Message-ID: <346ced6b.754999@smtp-gw01.ny.us.ibm.net> In-Reply-To: <199711140301.OAA11983@godzilla.zeta.org.au> References: <199711140301.OAA11983@godzilla.zeta.org.au>
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On Fri, 14 Nov 1997 14:01:41 +1100, Bruce Evans <bde@zeta.org.au> 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
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