Differences

This shows you the differences between two versions of the page.

--- doc:appunti:hardware:eeepc_navit [2009/11/06 12:27] – niccolo
+++ doc:appunti:hardware:eeepc_navit [2011/04/22 13:00] (current) – [Installing the GPS daemon] niccolo
@@ Line 35: / Line 35: @@
 </code>
-===== Installing the GPS daemon =====
+===== Installing gpsd, the GPS daemon =====
+This was tested on Debian Squeeze 6.0.
 Before starting Navit the **gpsd** should be up and running. Install the gpsd package and configure it, this is the relevant part of **''/etc/default/gpsd''** file:
@@ Line 46: / Line 48: @@
 </file>
-It is convenient to let **udev** handle some operations: when I connect my **[[gps_logger_i_blue_747|i-Blue 747 USB GPS logger]]** I want gpsd to be started (if it was not). Just add the following line to the file **''/etc/udev/rules.d/z60_gpsd.rules''** and restart udev:
+This will start **''gpsd''** at bootstrap, it will wait for the GPS to be connected to the USB port. **Note:** when the USB is connected, ''udev'' will not start ''gpsd'' if it is not already running (i.e. when ''START_DAEMON="false"'').
+**''udev''** will handle the automatic connection of the GPS via USB, there is a script **''/lib/udev/rules.d/60-gpsd.rules''** in Debian Squeeze which includes the **[[gps_logger_i_blue_747|i-Blue 747 USB GPS logger]]**.
+For previous Debian releases just add the following line to the file **''/etc/udev/rules.d/z60_gpsd.rules''** and restart ''udev'':
 <file>
@@ Line 53: / Line 59: @@
 </file>
-When the GPS is plugged into the USB port, udev creates the **''/dev/gps0''** device and starts **gpsd**. When the GPS is unplugged the Unix device is removed, but the daemon remains running.
+When the GPS is plugged into the USB port, ''udev'' creates the **''/dev/gps0''** device, when the GPS is unplugged the Unix device is removed and the daemon remains running.
 A simple test to check that gpsd is working, is to run **''gpspipe -r''** (provided by the ''gpsd-clients'' package), it should print out the NMEA messages recevied from the GPS:
@@ Line 69: / Line 75: @@
 $GPGGA,112814.000,4353.5310,N,01106.0969,E,0,3,,102.4,M,47.6,M,,*4B
 </code>
+==== Problem #1: plug/unplug ====
+When a gps client opens a connection with gpsd, it starts receiving data. If GPS device is unplugged and plugged again, the connection does not restart automatically. A workaround is to execute **''gpspipe -r n1''** into another terminal to force device re-opening.
+I hacked **''/lib/udev/gpsd.hotplug''**, adding the execution of that command when the device is re-added. This is the patch:
+<code>
+--- gpsd.hotplug.orig   2010-06-02 23:03:02.000000000 +0200
++++ gpsd.hotplug        2011-04-22 12:44:32.000000000 +0200
+@@ -114,6 +114,9 @@
+                 hotplug(os.getenv("ACTION"), os.getenv("DEVPATH"))
+             else:                      # Called by hand for testing
+                 gpsd_control(sys.argv[1], sys.argv[2])
++                if sys.argv[1] == 'add':
++                    # Wake-up all the listening clients.
++                    os.system("/usr/bin/gpspipe -r -n1 &")
+         except:
+             (exc_type, exc_value, exc_traceback) = sys.exc_info()
+             syslog.syslog("gpsd.hotplug: exception %s yields %s" % (exc_type, exc_value))
+</code>
+==== Problem #2: permissions ====
+With Debian Lenny there is a **permission problem**: if gpsd starts with no GPS connected, it switches to group **nobody**. When a GPS is connected, udev add the ''/dev/ttyUSB'' device as **root:dialout** and ''/lib/udev/gpsd.hotplug'' assigns mode **0660**. In this scenario gpsd cannot read the device.
+A workaround is to create a node for ''/dev/ttyS0'' owned by group dialout at boot time, even if no such device is present. Per default ''gpsd'' will read the group of this device and switches to that group.
-==== Problems to be solved with gpsd ====
+It should be possibile to create such a static device into **''/lib/udev/devices/''**, udev will copy it under ''/dev/'' at boot time:
-We want to be able to plug/unplug the GPS device in the USB port and gpsd should work seamless, but there are two problems:
-  - **Permissions**: if gpsd starts with no GPS is connected, it switches to group **nobody**. When a GPS is connected, udev add the /dev/ttyUSB device as **root:dialout** and /lib/udev/gpsd.hotplug assigns mode **0660**. In this scenario gpsd cannot read the device.
-  - **GPS unplug/plug**: when a gps client opens a connection with gpsd, it starts receiving data. If GPS device is unplugged and plugged again, the connection does not restart automatically. A workaround is to execute **''gpspipe -r n1''** to force device re-opening.
-A workaround at the first problem is to let /etc/init.d/udev create a node for /dev/ttyS0 at boot time, even if no devices are present. Per default gpsd will read the group of this device and switches to that group.
 <code>
-mknod -m 0660 /lib/udev/devices c 4 64
+mknod -m 0660 /lib/udev/devices/ttyS0 c 4 64
-chown root:dialout /lib/udev/devices
+chown root:dialout /lib/udev/devices/ttyS0
 </code>
-For the second problem I hacked **''/lib/udev/gpsd.hotplug''**, adding the execution of a script when the device is re-added:
-<code python>
-    if action == 'add':
-        # Force the group-read & group-write bits on, so gpsd will still be
-        # able to use this device after dropping root privileges.
-        os.chmod(argument, stat.S_IMODE(os.stat(argument)[stat.ST_MODE])|0660)
-        connect.sendall("+%s\r\n" % argument)
-        connect.recv(12)
-        os.system('/usr/local/bin/gps-reopen')
-</code>
-The script is simple this:
-<code bash>
-#!/bin/sh
-/bin/echo /usr/bin/gpspipe -r -n1 | /usr/bin/at now
-</code>
-Don't ask me why I need running gpspipe it via **at**, I suspect there is the need of a controlling terminal, etc...
 ===== Navigation =====