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Path: sserve!newshost.anu.edu.au!munnari.oz.au!yoyo.aarnet.edu.au!news.adelaide.edu.au!news.cs.su.oz.au!metro!ultima!kralizec.zeta.org.au!not-for-mail From: bde@kralizec.zeta.org.au (Bruce Evans) Newsgroups: comp.os.386bsd.questions Subject: Re: 8 16550 ports possible on FreeBSD 1.0 or 1.1? Date: 7 Apr 1994 17:56:42 +1000 Organization: Kralizec Dialup Unix Sydney - +61-2-837-1183, v.32bis v.42bis Lines: 20 Message-ID: <2o0ebq$kpb@kralizec.zeta.org.au> References: <Cn6nFx.280@du.edu> <CnpGrF.15B@luva.stgt.sub.org> <2nsipi$9lr@mojo.eng.umd.edu> NNTP-Posting-Host: kralizec.zeta.org.au >Actually, 16550 UARTS are a *lot* faster, although they stink for >mouse use. Does the sio code read the on chip FIFOs? Actually, they are normally limited by the serial board's Xtal to the same speed (115200 bps) as 8250 and 16450 UARTs, and sio has no trouble handling this speed, at least for less than 8 active ports. 16550's have less overheads; this sometimes translates to a faster speed. sio sets up the FIFOs with the maximum trigger level to minimise the overheads at the cost of increasing interrupt latency. You might need to use the FIFO_TRIGGER option to reduce the latency for 8 ports. Many operating systems have abysmal interrupt latency from other parts of the system and need to set the minimum trigger level for the serial ports to work even at low speeds like 19200. They get almost no benefits from the receiver FIFOs. sio used to always use the FIFOs if they exist. This is fixed in 1.1-BETA. You need to set flag 0x02 in the config for mouse ports. Also, mouse ports should have a slow speed (1200 bps) so that sio's software FIFOs don't cause the same problems as the h/w FIFOs. -- Bruce Evans bde@kralizec.zeta.org.au