From owner-freebsd-hackers Sat Feb 24 02:17:11 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id CAA13859 for hackers-outgoing; Sat, 24 Feb 1996 02:17:11 -0800 (PST) Received: from godzilla.zeta.org.au (godzilla.zeta.org.au [203.2.228.19]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id CAA13848 for ; Sat, 24 Feb 1996 02:16:58 -0800 (PST) Received: (from bde@localhost) by godzilla.zeta.org.au (8.6.12/8.6.9) id VAA30131; Sat, 24 Feb 1996 21:15:33 +1100 Date: Sat, 24 Feb 1996 21:15:33 +1100 From: Bruce Evans Message-Id: <199602241015.VAA30131@godzilla.zeta.org.au> To: msmith@atrad.adelaide.edu.au, petzi@zit.th-darmstadt.de Subject: Re: 230.400 bps on serial port Cc: hackers@FreeBSD.org Sender: owner-hackers@FreeBSD.org Precedence: bulk >> I need a reliable data transfer rate of 230.400 bps on the serial port for >> PPP. Can that be done ? getty only has a setting for 115.200 bps. I have a >> Gigabyte 586 ATEP mainboard with FIFOs. Can I use them for 230.400 bps, and >> how ? Or should I buy a special serial card for that ? >... >Note that at the speed you suggest a 16550 UART will be generating around >15,000 interrupts per second. This will place a _serious_ load on your >system, and if you're using IDE disk, may cause you to suffer communications >problems. All wrong. - 230400 bps full speed bidirectional generates at most 23040 / 16 + 23040 / 14 = 3085 interrupts/second. - 15000 serial interrupts/second isn't a _serious_ load under FreeBSD. On a 486/33, 23040 serial interrupts/second for full speed bidirectional through a 16450 has an total (user + sys + intr) overhead overhead of about 33%. This is only a serious overhead :-). On the same system, the interrupt overhead for a slow (1.25MB/sec) IDE disk is 56% for 2500 interrupts/second, and the overhead for an 1100K/sec WD8013EBT ISA ethernet card is 21% Sys + 54% Intr for 756 interrupts/second. - IDE disks have no effect on serial communications under FreeBSD. (Bus-hogging DMA controllers may have an adverse affect if they steal too many cycles.) Bruce