Date: Thu, 19 Oct 1995 16:37:01 -0700 From: David Greenman <davidg@Root.COM> To: root@spiffy.cybernet.com Cc: hackers@freebsd.org Subject: Re: Bragging rights.. Message-ID: <199510192337.QAA00227@corbin.Root.COM> In-Reply-To: Your message of "Thu, 19 Oct 95 19:53:59 EDT." <XFMail.951019190335.root@spiffy.cybernet.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)? Apparantly, *some* 16550 UARTs will do this, but as far as I know, this would be overclocking most versions out there and might result in the part overheating (or simply not working at 230K baud). -DG
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