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added USB compendium to documentation and made related FAQ entry
git-svn-id: https://svn.fhem.de/fhem/trunk@353 2b470e98-0d58-463d-a4d8-8e2adae1ed80
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borisneubert
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@ -492,3 +492,4 @@
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- feature: structure module for big installations
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- feature: Cost Control in 15_CUL_EM (CostPerUnit, BasisFeePerMonth)
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- feature: add counter differential per time in 81_M232Counter.pm
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- feature: added USB compendium to documentation
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141
fhem/docs/USB.html
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141
fhem/docs/USB.html
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<html>
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<head>
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<title>USB compendium</title>
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</head>
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<body>
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<H1>USB compendium</H1>
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Several fhem users are plagued by spontaneous disconnects/reconnects of USB
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devices. This is not an issue of fhem but a problem of hardware and/or USB
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drivers.<P>
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This document summarizes some findings on the issue. They are taken from
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users' experience and from a web research. This compendium is written for Linux
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users.
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<H2>A. Problem description</H2>
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USB devices spontaneously disconnect from the bus. They are reconnected after
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some time ranging from zero to many seconds. fhem global log shows messages like
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<pre>
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2009.01.12 19:22:14 1: USB device /dev/elv_fhz1300pc disconnected, waiting to reappear
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2009.01.12 19:22:19 1: USB device /dev/elv_fhz1300pc reappeared
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</pre>
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A look into the kernel message log with
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<pre>
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grep usb /var/log/messages | tail -n 100 | less
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</pre>
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shows messages like
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<pre>
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Jan 12 19:22:14 bunkertor kernel: usb 10-2.1: USB disconnect, address 59
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Jan 12 19:22:14 bunkertor kernel: usb 10-2.1.1: USB disconnect, address 61
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Jan 12 19:22:14 bunkertor kernel: usb 10-2.4: USB disconnect, address 60
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Jan 12 19:22:14 bunkertor kernel: usb 10-2: reset full speed USB device using uhci_hcd and address 2
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Jan 12 19:22:14 bunkertor kernel: usb 10-2.1: new full speed USB device using uhci_hcd and address 62
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.1: not running at top speed; connect to a high speed hub
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.1: configuration #1 chosen from 1 choice
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.1: New USB device found, idVendor=04b4, idProduct=6560
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.4: new full speed USB device using uhci_hcd and address 63
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.4: configuration #1 chosen from 1 choice
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.4: FTDI USB Serial Device converter now attached to ttyUSB0
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.4: New USB device found, idVendor=0403, idProduct=e0ef
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.4: Product: ELV EM 1010 PC
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.4: Manufacturer: ELV AG
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Jan 12 19:22:15 bunkertor kernel: usb 10-2.1.1: new full speed USB device using uhci_hcd and address 64
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Jan 12 19:22:16 bunkertor kernel: usb 10-2.1.1: configuration #1 chosen from 1 choice
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Jan 12 19:22:16 bunkertor kernel: usb 10-2.1.1: FTDI USB Serial Device converter now attached to ttyUSB1
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Jan 12 19:22:16 bunkertor kernel: usb 10-2.1.1: New USB device found, idVendor=0403, idProduct=e0e8
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Jan 12 19:22:16 bunkertor kernel: usb 10-2.1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
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Jan 12 19:22:16 bunkertor kernel: usb 10-2.1.1: Product: ELV FHZ 1300 PC
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Jan 12 19:22:16 bunkertor kernel: usb 10-2.1.1: Manufacturer: ELV AG
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Jan 12 19:22:16 bunkertor kernel: usb 10-2.1.1: SerialNumber: xxxxxxxxxxx
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</pre>
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<H2>B. Possible reasons and remedies</H2>
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<H3>1. Not enough power on the bus</H3>
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FHZ1300PC directly connected to the computer's built-in USB ports does not work
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at all or seizes to work after short time. This is likely due to the USB's
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inability to provide sufficient power to the connected
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devices. Use of a powered hub seems to cure the problem in some cases
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(confirmed, see [6]).
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<H3>2. Mixture of USB 1.1 and USB 2.0 devices</H3>
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Use of an USB 1.1 hub to connect USB 2.0 devices and vice versa might lead to
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timing problems (see [3]). Consistent use of either USB 1.1 or USB 2.0 devices
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might be a cure (unconfirmed).
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<H3>3. Timing problems</H3>
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It was suggested that late answers from a device make the driver think that it
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has gone away. This would lead to a disconnect. followed by a reconnect when
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the device's reply arrives. Changing the timeouts
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might be a cure. It is not known how to achieve this (see [5]).
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<H3>4. Electromagnetic interferences</H3>
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Bad shielding of cables or devices might lead to interferences with electric
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devices nearby (fridges, light switches, ...). A computer can cope with this
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problem better or worse. Changing the computer's hardware helps (confirmed,
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see [7]). If this is not feasible, use a ferrite ring (see [8] for instance)
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or two around the ends of the cable (unconfirmed).
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<H3>5. USB Power management</H3>
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The linux kernel USB driver supports power management. If there is no activity
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on the USB for a certain time, the port is switched to powersaving which leads
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to a disconnect of the device (see [3]). Details on
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linux power management are found in [4]. In short, you can turn off power
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management in general if you do
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<pre>
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echo -1 >/sys/module/usbcore/parameters/autosuspend
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</pre>
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or, for a specific device,
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<pre>
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echo on > /sys/bus/usb/devices/DEVICEID/power/level
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</pre>
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with DEVICEID substituted by the device's ID.
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<H3>6. USB extenders</H3>
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To increase the maximum cable length from 5 meters to 10 meters, so-called
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USB extenders are on sale. The consist of a fixed passive 1-port hub at the end of
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an USB cable. This drives the USB to its limits and may cause all sorts of
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problems on the bus. Either do not use USB extenders (confirmed, see [10]) at all
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or put an active (self-powered) hub in the middle (unconfirmed).
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<H2>C. Suggested reading</H2>
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[1] <A HREF="http://www.mikrocontroller.net/topic/116263">http://www.mikrocontroller.net/topic/116263</A><BR>
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[2] <A HREF="http://www.ti.com/sc/docs/apps/msp/intrface/usb/emitest.pdf">http://www.ti.com/sc/docs/apps/msp/intrface/usb/emitest.pdf</A><BR>
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[3] <A HREF="http://forum.soft32.com/linux/solution-usb-disconnect-problems-usb-ftopict345989.html">http://forum.soft32.com/linux/solution-usb-disconnect-problems-usb-ftopict345989.html</A><BR>
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[4] /usr/src/linux/Documentation/usb/power-management.txt<BR>
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[5] Google group FHZ1000 users on Linux, Message-ID: beb1c8d2-ec08-4ded-bc9b-2c0fc856fa09@e1g2000pra.googlegroups.com<BR>
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[6] Google group FHZ1000 users on Linux, Message-ID: 200812241129.01819.omega@online.de<BR>
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[7] Google group FHZ1000 users on Linux, Message-ID: 930a1555-3eda-49ce-82d9-3ecc617f5e9c@a26g2000prf.googlegroups.com<BR>
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[8] <A HREF="http://www.reichelt.de/?;ACTION=3;LA=4;GROUP=B522;GROUPID=3187;ARTICLE=7674;START=0;SORT=preis;OFFSET=1000;SID=26j@QMWawQARoAAFcmBVM2b30b32eb7a0d90a6833475d294db8c2">http://www.reichelt.de/?;ACTION=3;LA=4;GROUP=B522;GROUPID=3187;ARTICLE=7674;START=0;SORT=preis;OFFSET=1000;SID=26j@QMWawQARoAAFcmBVM2b30b32eb7a0d90a6833475d294db8c2</A><BR>
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[9] <A HREF="http://www.usb.org/developers/usbfaq/">http://www.usb.org/developers/usbfaq/</A><BR>
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[10] Google group FHZ1000 users on Linux, Message-ID: 2aac5192-1966-4939-a8ff-73d1e0b67506@w24g2000prd.googlegroups.com<BR>
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</body>
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</html>
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@ -61,6 +61,11 @@ messages from my FHT80b. How to switch back to the actuator:0% messages?</a>
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<a href="#faq17">17. I have problem receiving data, I get "Bad CRC" or "Oversized message."</a><br>
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<a href="#faq18">18. My FHZ1X00PC gets all time automatically disconnected and
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reconnected. My log shows "USB device /dev/elv_fhz1300pc disconnected, waiting to reappear".
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What is wrong with my USB?
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</a><br>
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<br/>
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<br/>
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@ -270,7 +275,7 @@ by fhem.pl?</b>
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# Get the second word, so we can compare it.
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FHZ> { my @a = split(" ", $value{myfht});; $a[1] }
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23.8
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23.8
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# Set the ventilator on now, if its too hot.
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FHZ> { my @a = split(" ", $value{myfht});; fhem("set ventilator on") if($a[1] > 25.0) }
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@ -399,6 +404,18 @@ messages from my FHT80b. How to switch back to the actuator:0% messages?
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</pre>
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</ul>
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<a name="faq18">
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<b>18. My FHZ1X00PC gets all time automatically disconnected and
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reconnected. My log shows "USB device /dev/elv_fhz1300pc disconnected, waiting to reappear".
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What is wrong with my USB?
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</b>
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<ul>
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Several fhem users are plagued by spontaneous disconnects/reconnects of USB
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devices. This is not an issue of fhem but a problem of hardware and/or USB drivers.
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See <a href="USB.html">USB compendium</a> for help.
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</ul>
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<br>
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</body>
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