Add support for Jetson AGX

doc/installation_jetson.md

@@ -8,24 +8,49 @@
 
 1. **Prerequisites:**
 
-  * **Jetson Nano** or **Jetson TX2** board (may also work on other Jetson devices)
-  * RealSense **D415**, **D435**, **D435i**, **SR300** or **T265** Camera
+  * NVIDIA® **Jetson Nano™**, **Jetson TX2™** and **Jetson AGX Xavier™** board (may also work on other Jetson devices)
+  * RealSense **D415**, **D435**, **D435i**, **D455**, **L515**, **SR300** and **T265** Camera devices.
 
 
-2. Follow [official instructions](https://developer.nvidia.com/embedded/learn/get-started-jetson-nano-devkit) to get your board ready. This guide will assume you are using official **Ubuntu 16.04** image from NVidia. We strongly recommend enabling the Barrel Jack connector for extra power (See [jetsonhacks.com/jetson-nano-use-more-power/](https://www.jetsonhacks.com/2019/04/10/jetson-nano-use-more-power/) to learn how)
+2. **Establish Developer's Environment**
+Follow [official instructions](https://developer.nvidia.com/embedded/learn/getting-started-jetson) to get your board ready. This guide will assume you are using **NVIDIA® L4T Ubuntu 16.04/18.04** image. Note that in most cases it is necessary to install a toll named "SDK Manager" to flash and install **Jetson** boards with both the L4T (Linux for Tegra) and NVIDIA-specific software packages (CUDA, Tensor Flow, AI, etc.)
+For **Jetson Nano™** we strongly recommend enabling the Barrel Jack connector for extra power (See [jetsonhacks.com/jetson-nano-use-more-power/](https://www.jetsonhacks.com/2019/04/10/jetson-nano-use-more-power/) to learn how)
 
   ![Jetson Nano](./img/jetson.jpg)
 
-> **Kernel Patches?** - There is a lot of confusion surrounding kernel patching for NVidia Jetson. [Previous versions](https://github.com/IntelRealSense/librealsense/blob/v2.29.0/doc/installation_jetson.md) of this document as well as [jetsonhacks.com guide](https://www.jetsonhacks.com/2019/05/16/jetson-nano-realsense-depth-camera/) are suggesting different patching strategies. While manual patching is still viable, starting with librealsense 2.24 (and 2.26 for the D435i) there is a better way:
+3. **Choose LibRealSense SDK Backend**  
+Librealsense2 SDK supports two API for communication with RealSense device on Linux platforms:
+    1. Linux native kernel drivers for UVC, USB and HID (Video4Linux and IIO respectively)
+    2. Using `RSUSB` - user-space implementation of the UVC and HID data protocols, encapsulated and activated by selecting the SDK's `-DFORCE_RSUSB_BACKEND` flag (a.k.a. `-DFORCE_LIBUVC` with SDK versions prior to v.2.30).  
 
-3. Register the server's public key:  
-```
-sudo apt-key adv --keyserver keys.gnupg.net --recv-key F6E65AC044F831AC80A06380C8B3A55A6F3EFCDE || sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-key F6E65AC044F831AC80A06380C8B3A55A6F3EFCDE
-```
+  When the second method is selected Librealsense2 communicates with the devices using the standard USB driver, while the higher-level protocols  (UVC/HID) stacks are compiled directly into the SDK.
+  Currently the two interfaces are mutually-exclusive, thus the choice taken during the SDK configuration stage (CMakes) predefines the selected backend API.
 
-> In case the public key cannot be retrieved, check and specify proxy settings: `export http_proxy="http://<proxy>:<port>"`, and rerun the command. See additional methods in the following [link](https://unix.stackexchange.com/questions/361213/unable-to-add-gpg-key-with-apt-key-behind-a-proxy).  
+  As a general rule it is recommended to use the native kernel drivers, especially in production environment.
+The second method augments the native installation and allows for a fully-functional SDK deployment at the expense of certain performance and functional limitations (e.g. multi-cam).
+The list of requirements for the second method comprise of a basic USB driver and GCC compiler, thus making it attractive for prototyping and demos in new/previously-unsupported environments.
 
-4. Add the server to the list of repositories:
+  If that's the case, what is the dilemma?
+
+  In order to enable the full capabilities of RealSense devices certain modifications in the kernel (driver) modules shall be applied, such as support of Depth-related streaming formats and access to per-frame metadata attributes. There is a small set of generic kernel changes that are mostly retrofitted with more advanced kernel versions aimed at improving the overall drivers stability.
+
+  NVIDIA's L4T delivers an Ubuntu-based distribution with a customized kernel based on version 4.9. The way the kernel is configured and deployed is different from a desktop Ubuntu image with two notable differences being the list of kernel modules included in default configuration and the way a new image is flashed.
+
+  And while it is possible to rebuild and flash a new kernel image the procedure can be perceived as challenging and shall be performed with extra caution.
+This guide comes with a script that allows to modify the kernel modules with Librealsense2-related patches without replacing the kernel image. The script has been verified with **Jetson AGX Xavier™** board using L4T versions 4.2.3, 4.3 and 4.4 (Sept 2020). Scroll to the end of the guide for details.
+
+
+4. **Install with Debian Packages**  
+Note that this method provides binary installation compiled using the `-DFORCE_RSUSB_BACKEND=true` option elaborated above.
+
+  1. Register the server's public key:  
+  ```
+  sudo apt-key adv --keyserver keys.gnupg.net --recv-key F6E65AC044F831AC80A06380C8B3A55A6F3EFCDE || sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-key F6E65AC044F831AC80A06380C8B3A55A6F3EFCDE
+  ```
+
+    > In case the public key cannot be retrieved, check and specify proxy settings: `export http_proxy="http://<proxy>:<port>"`, and rerun the command. See additional methods in the following [link](https://unix.stackexchange.com/questions/361213/unable-to-add-gpg-key-with-apt-key-behind-a-proxy).  
+
+  2. Add the server to the list of repositories:
 
   * Ubuntu 16:  
   ```
@@ -37,19 +62,73 @@ sudo apt-key adv --keyserver keys.gnupg.net --recv-key F6E65AC044F831AC80A06380C
   sudo add-apt-repository "deb http://realsense-hw-public.s3.amazonaws.com/Debian/apt-repo bionic main" -u
   ```
 
-5. Install the SDK:
-```
-sudo apt-get install librealsense2-utils
-sudo apt-get install librealsense2-dev
-```
-![installation](./img/install-jetson.png)
+  3. Install the SDK:
+  ```
+  sudo apt-get install librealsense2-utils
+  sudo apt-get install librealsense2-dev
+  ```
+  ![installation](./img/install-jetson.png)
+
 
-> With `dev` package installed, you can compile an application with **librealsense** using `g++ -std=c++11 filename.cpp -lrealsense2` or an IDE of your choice. To get started with RealSense using **CMake** check out [librealsense/examples/cmake](https://github.com/IntelRealSense/librealsense/tree/master/examples/cmake)
+  > With `librealsense2-dev` package installed, you can compile an application with **librealsense** using `g++ -std=c++11 filename.cpp -lrealsense2` or an IDE of your choice. To get started with RealSense using **CMake** check out [librealsense/examples/cmake](https://github.com/IntelRealSense/librealsense/tree/master/examples/cmake)
 
-6. Reconnect the RealSense device and run: `realsense-viewer` to verify the installation:
+  4. Reconnect the RealSense device and run: `realsense-viewer` to verify the installation:
 
   ![d400](./img/jetson-d400.png) ![t265](./img/jetson-t265.png)
 
   You can also double-TAB after typing `rs-` to see the full list of SDK examples.
-
-> **What about Building from Source?** - you can still build the SDK from source. To avoid kernel patching prerequisites we recommend building with `-DFORCE_LIBUVC=true` CMake flag. See [libuvc_installation.sh](https://github.com/IntelRealSense/librealsense/blob/master/scripts/libuvc_installation.sh). If you have CUDA dev-kit installed, don't forget to add `-DBUILD_WITH_CUDA=true` for better performance.
+
+## Building from Source using RSUSB Backend
+
+**Use the RSUSB backend without the kernel patching**
+
+  * In order to build the SDK using the `RSUSB` method and avoid the kernel patching procedure, please refer to [libuvc_installation.sh](https://github.com/IntelRealSense/librealsense/blob/master/scripts/libuvc_installation.sh) script for details. If you have CUDA dev-kit installed, don't forget to add `-DBUILD_WITH_CUDA=true` for optimal performance.
+
+ ## Building from Source using Native Backend
+
+ **Use the V4L Native backend by applying the kernel patching**
+
+   The method was verified with **Jetson AGX** boards with JetPack **4.2.3**[L4T 32.4.3], **4.3**[L4T 32.3.1] and **4.4**[L4T 32.2.1]. 
+
+   The medhoe has not yet been verified on the **Jetson Nano** board.
+
+  * **Prerequisite**
+
+    * Verify the board type and Jetpack versions compatibility.  
+    * Verify internet connection.  
+    * Verify the available space on flash, the patching process requires **~2.5Gb** free space  
+       >df -h
+
+    * Configure the Jetson Board into Max power mode (desktop -> see the upper right corner)  
+    * Disconnect attached USB/UVC cameras (if any).  
+
+  * **Build and Patch Kernel Modules for Jetson L4T** 
+
+    1. Navigate to the root of libreansense2 directory.  
+    2. Run the script (note the ending characters - `L4T`)  
+    ```
+    ./scripts/patch-realsense-ubuntu-L4T.sh  
+    ```
+    * The script will run for about 30 minutes depending on internet speed and perform the following tasks:  
+
+      a. Fetch the kernel source trees required to build the kernel and its modules.  
+      b. Apply Librealsense-specific kernel patches and build the modified kernel modules.  
+      c. Try to insert the modules into the kernel.  
+
+    ![d400](./img/jetson_l4t_kernel_patches.png)
+
+  * **Build librealsense2 SDK**  
+
+    1. Navigate to the SDK's root directory.  
+    2. Follow the [Ubuntu installation guide](./installation.md) to install the missing components and configuration items:  
+    ```
+    sudo apt-get install git libssl-dev libusb-1.0-0-dev pkg-config libgtk-3-dev -y
+    ./scripts/setup_udev_rules.sh  
+    mkdir build && cd build  
+    cmake .. -DBUILD_EXAMPLES=true -DCMAKE_BUILD_TYPE=release -DFORCE_RSUSB_BACKEND=false -DBUILD_WITH_CUDA=true && make -j$(($(nproc)-1)) && sudo make install
+    ```
+       The CMAKE `-DBUILD_WITH_CUDA=true` flag assumes CUDA modules are installed. If not, please reconnect the board to the Ubuntu Host PC and use NVIDIA `SDK Manager` tool to install the missing components.
+
+  * **Connect Realsense Device, run `realsense-viewer` and inspect the results**
+
+       ![d400](./img/jetson_l4t_sensors_md.png)