Date: Sat, 29 Jun 1996 21:01:42 +1000 From: Bruce Evans <bde@zeta.org.au> To: jparnas@jparnas.cybercom.net, msmith@atrad.adelaide.edu.au Cc: Kevin_Swanson@BLaCKSMITH.com, bsdi-users@bsdi.com, hardware@FreeBSD.org, stesin@elvisti.kiev.ua Subject: Re: muliport boards - building a PPP dialup server Message-ID: <199606291101.VAA02125@godzilla.zeta.org.au>
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>The 16550 can be clocked safely to several megabits/s. The problem >with their implementation in the PC is that they're clocked at >~1.8MHz, which limits them to 115k2. The 16650 is a 16550 with a 32-bye I suppose the highly integrated 16550 clones can't be clocked so high. Especially if their clock is integrated. >FIFO. Neither are suitable for 512KBps; at this speed you have a new >byte arriving every 16us, or a full FIFO after only 512usec. This is too >fast for anything other than a dedicated system. That's not fast. A 386/20 can easily handle an interrupt every 86 us for a full (1 byte :-) fifo on an 8250. The problem is to move the data fast enough. 40 us every 512 us to move 32 bytes may be acceptable for one port, but it won't work for 16 ports. >> Its amazing that one of the slowest protocols on the computer is the >> one that gives most people the most trouble. The UARTs seem to be >> one step behind as do the motherboard/software companies. I'm of It seems more like 10 generations (with 10 steps per generation :-). >> course talking about RS/232 system, which has been a problem with >> some software at anything over 300 baud at times (even with 9600 >> baud modems operating at 300 baud. Sun requires a special board at >> least on my sparc 2. So there's no problem with a 10mbit/sec >> ethernet, but 1200baud to 1/20 of the original ethernet speed is >> even on workstations. FreeBSD software is only one generation behind. It routinely handles 115200 bps. Bruce
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