From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-iio-owner@vger.kernel.org>
Received: from mail-io0-f178.google.com ([209.85.223.178]:36703 "EHLO
	mail-io0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752574AbbHSV3N (ORCPT
	<rfc822;linux-iio@vger.kernel.org>); Wed, 19 Aug 2015 17:29:13 -0400
Received: by iodv127 with SMTP id v127so24733566iod.3
        for <linux-iio@vger.kernel.org>; Wed, 19 Aug 2015 14:29:12 -0700 (PDT)
Date: Wed, 19 Aug 2015 16:29:07 -0500
From: Michael Welling <mwelling@ieee.org>
To: Greg Wilson-Lindberg <GWilson@sakuraus.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>
Subject: Re: BBB IIO ADC access not working
Message-ID: <20150819212906.GC29773@deathstar>
References: <20150818173703.GA5096@deathstar>
 <782E3A02C2EB2347BEA6DEA69DC7AB86021D3CBD42D8@sfamail.SAKURAUS.LOCAL>
 <20150818181324.GC5096@deathstar>
 <782E3A02C2EB2347BEA6DEA69DC7AB86021D3CBD4340@sfamail.SAKURAUS.LOCAL>
 <20150818223114.GA1372@deathstar>
 <782E3A02C2EB2347BEA6DEA69DC7AB86021D3CBD43DF@sfamail.SAKURAUS.LOCAL>
 <20150819175230.GA29773@deathstar>
 <782E3A02C2EB2347BEA6DEA69DC7AB86021D3CBD444B@sfamail.SAKURAUS.LOCAL>
 <20150819204847.GA28779@deathstar>
 <782E3A02C2EB2347BEA6DEA69DC7AB86021D3CBD4454@sfamail.SAKURAUS.LOCAL>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <782E3A02C2EB2347BEA6DEA69DC7AB86021D3CBD4454@sfamail.SAKURAUS.LOCAL>
Sender: linux-iio-owner@vger.kernel.org
List-Id: linux-iio@vger.kernel.org

On Wed, Aug 19, 2015 at 02:13:10PM -0700, Greg Wilson-Lindberg wrote:
> 
> I'm not using /sys/bus/iio/devices/iio:device0/in_voltageX_raw in my program, 
> I'm using the iio buffer system.
> 
> I tried using cat /sys/bus/iio/devices/iio:device0/in_voltageX_raw while my
> program was running and it worked a couple of times, and got busy a bit also,
> then the touch screen locked up.

This is expected because when the buffer is enabled the device IS busy.
> 
> I have not tried to use /sys/bus/iio/devices/iio:device0/in_voltageX_raw from
> in my program, I was hoping for a lighter weight access that didn't require 
> so many opens & closes. I'm under the impression that I can only get one 
> reading per open if I try to read /sys/bus/iio/devices/iio:device0/in_voltageX_raw.
> Or can I get multiple readings if I do multiple reads.
>

You should be able to keep the file descriptor open and perform multiple reads.

It is necessary lseek before reading from the same channel again.

lseek(fd, 0, SEEK_SET);

You will need a separate file descriptor for each channel.