From owner-freebsd-hackers Fri Mar 17 01:53:48 1995 Return-Path: hackers-owner Received: (from majordom@localhost) by freefall.cdrom.com (8.6.10/8.6.6) id BAA00178 for hackers-outgoing; Fri, 17 Mar 1995 01:53:48 -0800 Received: from godzilla.zeta.org.au (godzilla.zeta.org.au [203.2.228.34]) by freefall.cdrom.com (8.6.10/8.6.6) with ESMTP id BAA00172 for ; Fri, 17 Mar 1995 01:53:38 -0800 Received: (from bde@localhost) by godzilla.zeta.org.au (8.6.9/8.6.9) id SAA12539; Fri, 17 Mar 1995 18:52:32 +1000 Date: Fri, 17 Mar 1995 18:52:32 +1000 From: Bruce Evans Message-Id: <199503170852.SAA12539@godzilla.zeta.org.au> To: dufault@hda.com, freebsd-hackers@freefall.cdrom.com Subject: Re: Multiport serial cards Sender: hackers-owner@FreeBSD.org Precedence: bulk >I'm interested in a board that will let me receive continuous data at >28.8 on four ports without any problems. At roughly 300 us per >character that will mean we have to service each port every 4.8 ms with >a 16550, or roughly 1.2 ms per port. (Of course lots of times when >you're in the interrupt you'll be able to to serve more than one port) This is a small load for sio. The overhead using an AST/4 on a DX2/66 should be about 6% for input-only and 4% for output-only plus whatever you protocol handler adds. >I think I should use a board with a large FIFO, which I don't think >any of these have. A 1-char "FIFO" as found on 8250's should be adequate provided you have no bus-hogging devices. sio can handle continuous data in both directions at once at 115.2 on 2 ports (but not 3) on a 486DX/33 with 8250's. The system load for this is about 60% (too high for continuous use). A 486DX2/66 with 16550's can probably handle about 6 times as many ports. Bruce