From owner-freebsd-current Thu Oct 17 11:15:36 2002 Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id B4D1337B401 for ; Thu, 17 Oct 2002 11:15:35 -0700 (PDT) Received: from apollo.backplane.com (apollo.backplane.com [216.240.41.2]) by mx1.FreeBSD.org (Postfix) with ESMTP id 1788143E8A for ; Thu, 17 Oct 2002 11:15:35 -0700 (PDT) (envelope-from dillon@apollo.backplane.com) Received: from apollo.backplane.com (localhost [127.0.0.1]) by apollo.backplane.com (8.12.5/8.12.4) with ESMTP id g9HIFXPQ022795; Thu, 17 Oct 2002 11:15:33 -0700 (PDT) (envelope-from dillon@apollo.backplane.com) Received: (from dillon@localhost) by apollo.backplane.com (8.12.5/8.12.4/Submit) id g9HIFX3a022794; Thu, 17 Oct 2002 11:15:33 -0700 (PDT) (envelope-from dillon) Date: Thu, 17 Oct 2002 11:15:33 -0700 (PDT) From: Matthew Dillon Message-Id: <200210171815.g9HIFX3a022794@apollo.backplane.com> To: Don Bowman Cc: "'Kenneth P. Stox'" , FreeBSD current users Subject: Re: RE: Dedicating an interrupt to a PC-Card slot References: Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG :Doesn't sound like that fast an interrupt. The 16550 has a 16-byte :send and receive fifo. Set the rx interrupt @ 14, and the tx @ 2. :230400/8 = 28800 chars /s :28800 / 14 = 2057 interrupts / s. This should be well within reach :of a pentium-class machine. Not a good idea. If you set the rx fifo at 14 you will get fewer interrupts, sure, but you will also have less of a safety margin to process them before the rx fifo potentially overflows and you lose characters. This is why I changed the default fifo level from HIGH (14) to MEDH (8) a while back. In anycase, anything less then 10,000 interrupts a second ought to be fine. The real problem is still going to be other things in the system causing enough interrupt latency to result in lost characters. The most common culprit is X windows doing big bitblits to the video card / video memory, and I think having a non-DMA IDE interface can also cause problems. At 230400 baud and 10 bits per character (one start, one stop bit), a fifo level of 14 gives you 2 character times of safety, or approximately 86uS. At a fifo level of 8 you have 8 character times of safety or approximately 347uS. -Matt Matthew Dillon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message