From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vx0-f171.google.com (mail-vx0-f171.google.com [209.85.220.171]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id B4ECB200890 for ; Tue, 13 Mar 2012 21:36:13 -0700 (PDT) Received: by vcbfl15 with SMTP id fl15so2984552vcb.16 for ; Tue, 13 Mar 2012 21:36:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=o4c9T/qXKeWcFOQP70a3tNvXDgC75b6pkyWLW7h10oo=; b=w8Kb6PZUf076ei/hKznuu6DiK9x4NT7KmpI0hFREqEHG5aE2duYCm+gxS7xpbfKCfC 6lIBhwIG4itQVelOj5G6GVErGDng+I/LZ4bx6335SWBU9QFh91HlvSBlDiSKf6qabmU0 b8HxE64UScLWjWXpZv12iGysNtDUh8sP4M+TKcGm5jcSETpoVbZAq4rxmaGojGrSpKfo Jwz1NFBSSuF2K/yTnmG7WTycOZIBDagL42QBvT2KDXfqtDYDZpGRKF+nKhfRmMPfM18j 9lipbJ6Jw8ZKOPAT4Eq4LWng/8eNfO0sCJmwTswwx2SetQHXfAIXa1YLr+fpJ1zjZTfm ehFg== MIME-Version: 1.0 Received: by 10.52.93.138 with SMTP id cu10mr810145vdb.86.1331699772465; Tue, 13 Mar 2012 21:36:12 -0700 (PDT) Received: by 10.220.140.132 with HTTP; Tue, 13 Mar 2012 21:36:12 -0700 (PDT) In-Reply-To: References: <20120313230612.GA24800@thyrsus.com> Date: Tue, 13 Mar 2012 23:36:12 -0500 Message-ID: From: Patrick Maupin To: tz Content-Type: text/plain; charset=ISO-8859-1 Cc: thumbgps-devel@lists.bufferbloat.net Subject: Re: [Thumbgps-devel] Project clarification X-BeenThere: thumbgps-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 14 Mar 2012 04:36:14 -0000 On Tue, Mar 13, 2012 at 10:05 PM, tz wrote: > We could send an event OUT the USB host and timestamp it at the > device, returning when it saw it - this might be more accurate if this > is more granular than polling. I was definitely thinking of this when thinking of building the FPGA-based timestamp-everything unit. You're right that if we're willing to write USB device firmware, a lot of opportunities to gain tighter tolerances present themselves. This would be even more true if we pick a highspeed device. Another simple thing we could do with basic serial units is to loop back RTS to CTS so you can calculate round-trip time to put an upper bound on inbound delay. If we really want to consider our own firmware, we might consider something like nuttx running on either an Atmel part or an NXP LPC3131. Olimex has an NXP development board for $90.