Date: Tue, 11 Jul 2000 19:52:40 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: ohoyer@fbwi.fh-wilhelmshaven.de Cc: Brian Handy <handy@isass0.solar.isas.ac.jp>, freebsd-hardware@FreeBSD.ORG Subject: Re: Serial I/O thruput Message-ID: <Pine.BSF.4.21.0007111930160.24707-100000@besplex.bde.org> In-Reply-To: <396A21AC.A43F233E@nightfire.de>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, 10 Jul 2000, Olaf Hoyer wrote: > > However...I'm not sure how fast I can push data into the motherboard over > > these ports. I don't have any hardware yet (that's what the proposal is Not very fast. Maybe 90K/sec using 8 standard ports or 1 nonstandard one. > Well, the standard 16550 FIFO is capable of shovelling about 115200 bps. More like 1.5 Mbps, actually. Even 8250's can handle low speeds like 115200 bps. Standard hardware is bug for bug compatible with original pre-ISA hardware, so it uses a 1.8432 MHz crystal and can't go faster than 1.8432 * 10^5 / 16 = 115200 bps. > There are better chips available, that shall be able to do more than > (IIRC, 8 times) that value. YOu need some special drivers for that. Boards with higher frequency crystals are usually shipped with newer UARTS with larger FIFOs since feeble drivers/OSes can't drain the 16550 FIFO fast enough. This makes little difference under FreeBSD since the bottleneck is the ISA bus (or the slow interface to the PCI bus in the case of the pci cyclades-Y (non-16550) hardware), provided the CPU is not too slow (P5 or better). Some simple modifications are required to support speeds above 115200 bps under FreeBSD. The pc98 version of sio already has them. The cyclades driver is arbitrarily limited to 150000 bps (some versions of the hardware work at 300000 bps). Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.BSF.4.21.0007111930160.24707-100000>