Date: Thu, 19 Oct 1995 19:53:59 -0400 From: "Mark J. Taylor" <root@spiffy.cybernet.com> To: <hackers@freebsd.org> Subject: Re: Bragging rights.. Message-ID: <XFMail.951019190335.root@spiffy.cybernet.com> In-Reply-To: <199510192007.NAA29801@corbin.Root.COM>
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On 10/19/95 20:25:56 David Greenman wrote: [clip] > > Let me add a bit of sanity to this part of the discussion. 115200 baud async >will give you about 11.52Kbytes/second if you have no packet overhead. 115200 >baud sync will give you 14.40Kbytes/second if you have no packet overhead. > Why? Because we're talking bits - async is 8 data bits plus 1 start and 1 >stop bit...10 bits. With synchronous serial, it's just 8 data bits. So sync >always has the potential to give you 25% more bytes throughput at the same bit >rate compared to async. > Now with sync you'll also be running at a faster bit rate (128000bits/sec). >This is 16Kbytes/second. This is 38.9% faster. > >-DG As a slightly interested party, I'd like to ask: As mentioned recently on -hackers, isn't it possilbe to up the rate of the serial chip simply by doubling (or quadding) the rate of the xtal driving the chip? Many (most?) 16550 chips should be able to handle a Fmax higher than they are being driven, and with 16 byte FIFOS (set to trigger at 14 bytes), the interrupt overhead would not necessarily be increased. Is the same xtal trick applicable to sync serial, to get 32 KBytes/second @256000 bits/sec (as opposed to 28.8 KBytes/sec async serial @230400 bits/sec)? -Mark Taylor mtaylor@cybernet.com
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