examples: rh850: can_demo: Added documentation about using the Linux …

…can-utils 'canfdtest' with the CAN demo application.

Signed-off-by: Adrien Ricciardi <aricciardi@baylibre.com>

examples/rh850/can_demo/README.md

@@ -48,9 +48,49 @@ If you want to generate a `.srec` file to directly flash on the board, look at t
 
 ## Running
 
+### Using Kvaser CanKing
+
 Before starting the CAN demo application, connect the hardware setup and configure the Kvaser CanKing application as described in the above paragraphs.
 Then, click the CanKing `Go On Bus` button.
 Now, you can run the CAN demo application.
 
 The CAN demo application starts by sending a CAN frame with the CAN ID `0x123` and the string payload `Ready!`.
 After that, it waits for a CAN frame to be received. When a frame is received, it increments the CAN ID and all the payload bytes, then it sends the frame back.
+
+### Using canfdtest on Linux
+
+For this test we used `Ubuntu 23.10` as it is the first Ubuntu version containing a recent enough version of the `can-utils` package (the minimal required version of the `can-utils` package is `v2023.03`).
+
+* Install the required package :
+  ```
+  sudo apt install can-utils
+  ```
+  Note : it is also possible to build the `can-utils` package from sources to run it on older Linux versions (see [https://github.com/linux-can/can-utils/releases/tag/v2023.03](https://github.com/linux-can/can-utils/releases/tag/v2023.03)).
+* Start the CAN demo application on the board.
+* Then, execute the following commands on the Linux PC :
+  ```
+  # Configure the CAN interface for CAN-FD operations without bit rate switch
+  sudo ip link set can0 type can bitrate 1000000 dbitrate 1000000 fd on
+  sudo ip link set up can0
+
+  # Run the test (the PC generates the frames and the board sends the answers)
+  # Generate CAN-FD frames without bit rate switch
+  canfdtest -d -g -v can0
+  ```
+* When frames are correctly transmitted and received, the output of the program looks like :
+  ```
+  baylibre@baylibre:~$ canfdtest -d -g -v can0
+  interface = can0, family = 29, type = 3, proto = 1
+  .................................................................
+  ```
+* On another terminal on the PC, you can display the CAN bus load, showing that frames are being transmitted :  
+  Run the command : `canbusload -b can0@1000000`.  
+  The output of the program looks like :
+  ```
+  baylibre@baylibre:~$ canbusload -b can0@1000000
+  can0@1000000   963  131931  61632      0  13% |XX..................|
+
+  can0@1000000  1061  145357  67904      0  14% |XX..................|
+
+  can0@1000000  1012  138644  64768      0  13% |XX..................|
+  ```