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# udev rules for HDMI2USB devices
These directory contains udev rules for
[HDMI2USB devices](https://hdmi2usb.tv). While these devices *don't need* these
rules to operate correctly, they make things significantly nicer.
These udev rules do the following things;
* Generate `/dev/hdmi2usb` symlinks. Each entry is a directory which groups
together the usbdev, tty and video devices. There are three methods for
finding the board;
1) By number, first board == 0, second board == 1, etc.
```
/dev/hdmi2usb/by-num/all$N/{usbdev,tty,video}
/dev/hdmi2usb/by-num/all0/
/dev/hdmi2usb/by-num/$BOARDTYPE$N/{usbdev,tty,video}
/dev/hdmi2usb/by-num/opsis0/
```
2) By location on the USB bus;
```
/dev/hdmi2usb/by-path/usb.bus$X.port$Y{-hub.port$Z}*/{usbdev,tty,video}
/dev/hdmi2usb/by-path/usb.bus1.port2/
/dev/hdmi2usb/by-path/usb.bus3.port4-hub.port3/
/dev/hdmi2usb/by-path/usb.bus3.port4-hub.port3-hub.port1/
```
3) By serial number;
```
/dev/hdmi2usb/by-serial/$SERIALNO/{usbdev,tty,video}
/dev/hdmi2usb/by-serial/ffffd8803956c79a/
```
* Grant anyone on the system permission to access the HDMI2USB boards.
* Make modem-manager ignore the serial ports.
They work the following way;
* `98-hdmi2usb-xxx.rules` - These files tag the ENV with the HDMI2USB
information.
- `98-hdmi2usb-opsis.rules` - Rules for the Numato Opsis board.
- `98-hdmi2usb-atlys.rules` - Rules for the Digilent Atlys board.
* `99-hdmi2usb-xxx.rules` - These files use the tags to do things.
- `99-hdmi2usb-aliases.rules` - Creates the extra symlinks
- `99-hdmi2usb-permissions.rules` - Sets the permissions
- `99-hdmi2usb-mm-blacklist.rules` - Makes modem manager ignore the device
* `99-hdmi2usbaux-xxx.rules` - These files are used for HDMI2USB related
devices which don't really follow the proper rules.
- `99-hdmi2usbaux-cypress.rules` - Rules for an unconfigured Cypress FX2
(such as the Numato Opsis/Digilent Atlys in fail-safe mode).
- `99-hdmi2usbaux-ixo-usb-jtag.rules` - Rules for the boards when loaded with
ixo-usb-jtag.
* `hdmi2usb-human-path-helper.sh` is just a simple shell script which converts
the kernel naming into something human readable.
# Examining udev data
```
udevadm info --attribute-walk --name=/dev/ttyACM0
udevadm test /sys/class/tty/ttyACM0 2>&1 | less
udevadm test /sys/class/video4linux/video0 2>&1 | less
udevadm test $(udevadm info -q path -n /dev/bus/usb/003/109) 2>&1 | less
```
Useful docs:
* [udev Linux Man Page](http://linux.die.net/man/8/udev)
* [Linux kernel udev docs](https://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/udev.html)
* [Debian Wiki](https://wiki.debian.org/udev)
* [Oracle Docs on Device Management](https://docs.oracle.com/cd/E37670_01/E41138/html/ol_devices.html)
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