From owner-freebsd-hackers@FreeBSD.ORG Wed Jul 27 22:45:36 2005 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id CF6AA16A41F for ; Wed, 27 Jul 2005 22:45:36 +0000 (GMT) (envelope-from samuel.pierson@gmail.com) Received: from wproxy.gmail.com (wproxy.gmail.com [64.233.184.192]) by mx1.FreeBSD.org (Postfix) with ESMTP id 0D9D843D46 for ; Wed, 27 Jul 2005 22:45:35 +0000 (GMT) (envelope-from samuel.pierson@gmail.com) Received: by wproxy.gmail.com with SMTP id i22so280671wra for ; Wed, 27 Jul 2005 15:45:26 -0700 (PDT) DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:reply-to:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=PZSLKyo3we+DfeON13HtOgCzLR9GdwpRvE0fj1oEN50quH7leV9MY6FuHFIxVIdUOwFTtEHh2bBeqW9lIlHFiFQeUwQWXZHOVaztQKGiEli+HdXV/HNTO33wdoKfsa/rjKRUg0bXSyqFcH6ajfu56/Lk4i3ssaq8D9PKAOBrIuA= Received: by 10.54.32.18 with SMTP id f18mr534955wrf; Wed, 27 Jul 2005 15:45:26 -0700 (PDT) Received: by 10.54.144.1 with HTTP; Wed, 27 Jul 2005 15:45:26 -0700 (PDT) Message-ID: Date: Wed, 27 Jul 2005 17:45:26 -0500 From: Sam Pierson To: David Malone In-Reply-To: <200507261513.aa10533@salmon.maths.tcd.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline References: <200507261513.aa10533@salmon.maths.tcd.ie> Cc: FreeBSD Hackers Subject: Re: Atheros, hardware access layer, collisions X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Sam Pierson List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Jul 2005 22:45:36 -0000 On 7/26/05, David Malone wrote: > That's correct, but it probably takes a few microseconds for the > carries sense to kick in (if there wasn't a delay there would > be almost no need for the random backoff). That's why you'll > also have to have your transmissions synchronised very closely. > David. Since my project is running in adhoc mode, I noticed that there is a LOT of noise being generated by the two machines I want to use in order to generate a collision. The noise is the adhoc beacon being broadcast. Clearly they need to talk to each other, but I'd really like to quiet down the channel so I can attempt this collision. I found this in if_ath: /* NB: the beacon interval is kept internally in TU's */ and this in /sys/contrib/dev/ath/ah_desc.h =09HAL_TX_QUEUE_BEACON=09=3D 2,=09=09/* beacon xmit q */ =09HAL_TX_QUEUE_CAB=09=3D 3,=09=09/* "crap after beacon" xmit q */ and... # cat ah.h | grep interval * beacon interval (given in TU's) can also include flags u_int32_t bs_intval; /* beacon interval+flags */ #define HAL_BEACON_PERIOD 0x0000ffff /* beacon interval period *= / I think the carrier sensing is kicking in because the channel is not quiet due to the beacons. Do the tx q things matter? seems like the=20 hal_beacon_period would be the most important line, but I don't see how that flag (if it is one) can be used. -Sam