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--- projects:qtusb [2013/06/01 23:26] – [Linux] mkucia
+++ projects:qtusb [2013/06/04 23:23] – [Developing multi-platform USB applications with Qt] mkucia
@@ Line 1: / Line 1: @@
 ====== Developing multi-platform USB applications with Qt ======
-//24.05.2013 Freising, Germany//
+//Germany 24.05.2013//
-<WRAP center todo>
-This page is under construction
-</WRAP>
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@@ Line 50: / Line 45: @@
   * [[http://www.usb.org/developers/usbfaq#12| USB.org How do I get a USB VID, TID and PID?]]
   * [[http://www.ti.com/mcu/docs/mcuorphan.tsp?contentId=72713&DCMP=STELLARIS&| TI Stellaris USB VID/PID Sublicense Application]]
 ====== Software ======
@@ Line 174: / Line 168: @@
 </code>
 ===== Linux =====
-I am using Debian 6.0.7 (virtual machine).
+{{:projects:qt_usb_linux.png |}}
+I am using Debian 7 with LXDE.
 We cannot use windows-specific routines under Linux. To check if device is connected or not we will pool udev monitor.
@@ Line 182: / Line 177: @@
 If true plug-and-play is required it is better to use standard USB class (for example CDC).
-  * Qt Linux source code [TODO]
+ {{:projects:usb_gui.zip|Qt Linux source code}}
-==== Building libusbx ====
+==== Linking libraries ====
+If your system is up-to-date you will most likely have both libraries installed. You can link them using following qmake code:
+<code>
+LIBS += -L/usr/local/lib/ -lusb-1.0
+LIBS += -L/usr/lib/ -ludev
+</code>
+==== udev rules ====
+Create a rule for device by making a new file:
-  - Download the code from libusbx source forge download page
+  nano /etc/udev/rules.d/usb_led_bulk.rules
-  - Extract files
-  - Run standard sequence:
-    - ''./configure''
-    - ''make''
-    - ''make install''
-After that user should find ''libusb-1.0.a'' in local libraries catalog ''/usr/local/lib''
+with following content:
-It might be necessary to install required packages, see README.
+  SUBSYSTEMS=="usb", ATTRS{idVendor}=="1cbe", ATTRS{idProduct}=="0003", GROUP="users", MODE="0666", SYMLINK+="rgb_led"
+This will allow non-root users to access the device. Also device will be accessible through path ''/dev/rgb_led''
-==== Building systemd (libudev) ====
+Restart udev service for changes to take effect ''/etc/init.d/udev restart''
-  - Download most recent source from http://www.freedesktop.org/software/systemd/
-  - Extract
-  - Go to project directory
-  - Build library (additional packages might be required I had to build libdbus, see README):
-    - ''./configure''
-    - ''make''
-    - ''make install''
-TODO
-==== udev Rules ====
+There are more actions that udev rules can implement. For example launching application when device is connected.
-TODO
-Start with creating a rule for device
+==== Detecting device mount/remove ====
-  nano /etc/udev/rules.d/usb_led_bulk.rules
-  SUBSYSTEMS=="usb", ATTRS{idVendor}=="1cbe", ATTRS{idProduct}=="0003", GROUP="users", MODE="0666", NAME="rgb_led"
+udev allow user applications to receive messages on changes in devices filesystem.
+One can filter messages by subsystem and type.
+In our case we want to receive USB device notifications from USB subsystem (it also emits USB interface messages).
+Finally monitor is activated and file descriptor ([[wp>Unix_file_types#Socket|socket file]]) retrieved.
-This will allow non-root users to access the device. Also device will be accessible through path ''/dev/rgb_led''
+<code=c>
+// Create the udev object
+if (!(udev = udev_new()))
+[..]
-Restart udev service for changes to take effect ''/etc/init.d/udev restart''
+// Set up a monitor to monitor usb devices
+mon = udev_monitor_new_from_netlink(udev, "udev");
+// We want only to receive information about usb devices
+udev_monitor_filter_add_match_subsystem_devtype(mon, "usb", "usb_device");
+udev_monitor_enable_receiving(mon);
+fd = udev_monitor_get_fd(mon);
+</code>
+The messages need to be pooled periodically. I created timer that fires every 250 [ms].
+<code=c>
+// Start timer that will periodicaly check if hardware is connected
+monitorTimer = new QTimer(this);
+connect(monitorTimer, &QTimer::timeout, this, &MainWindow::monitorTimerTick );
+monitorTimer->start(250);
+</code>
+Timer code checks if there is a new message. select() returns amount of messages. In this case function is non-blocking but one can implement timeout easy here.
+<code=c>
+void MainWindow::monitorTimerTick()
+{
+    // Set up select
+    fd_set fds;
+    struct timeval tv;
+    int ret;
+    FD_ZERO(&fds);
+    FD_SET(fd, &fds);
+    tv.tv_sec = 0;
+    tv.tv_usec = 0;
+    ret = select(fd+1, &fds, NULL, NULL, &tv);
+    // Check if our file descriptor has received data.
+    if (ret > 0 && FD_ISSET(fd, &fds))
+    {
+</code>
+When new message is confirmed code check if it from our hardware by looking into vendor id and product id.
+If device matches, code checks type of event and emits appropriate Qt signal.
+<code=c>
+// Get the device
+if ( (dev = udev_monitor_receive_device(mon)) == NULL)
+[...]
+// Now check if the device is our rgb_led launchpad
+const char* str_action = udev_device_get_action(dev);
+const char* str_PID = udev_device_get_property_value(dev, "ID_MODEL_ID");
+const char* str_VID = udev_device_get_property_value(dev, "ID_VENDOR_ID");
+[...]
+// Compare strings and send signals
+if ( (strcmp(STR_PRODUCT_ID,str_PID) == 0) && (strcmp(STR_VENDOR_ID,str_VID) == 0) )
+{
+   if (strcmp("add",str_action) == 0)
+   {
+      emit signal_DeviceConnected();
+   }
+   else if (strcmp("remove",str_action) == 0)
+   {
+      emit signal_DeviceDisconnected();
+   }
+[...]
+    // If there are more events to process, do not wait for next tick!
+    if (ret-1 > 0)
+        monitorTimerTick();
+</code>
 ====== References ======
+  * http://libusbx.sourceforge.net/api-1.0/
   * http://www.signal11.us/oss/udev/
   * http://www.freedesktop.org/software/systemd/libudev/
+  * http://linux.die.net/man/8/udevadm
   * http://www.linuxforu.com/2012/06/some-nifty-udev-rules-and-examples/
   * http://www.reactivated.net/writing_udev_rules.html
-  * http://linux.die.net/man/8/udevadm
   * http://hackaday.com/2009/09/18/how-to-write-udev-rules/
+  * http://msdn.microsoft.com/en-us/library/windows/hardware/gg463179.aspx
 <WRAP todo>
   * Build single software package for MCU, Win and Linux
-  * add more references
 </WRAP>