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--- lkd:laboratoare:01 [2024/07/07 13:54]
daniel.baluta
+++ lkd:laboratoare:01 [2024/07/08 15:18] (current)
daniel.baluta
@@ Line 15: / Line 15: @@
 ==== Presentation ====
-  * follow slides at [[session 1]]
+  * follow slides at  {{:lkd:laboratoare:lkd_01.pdf| Session 1}}
 ==== Practical lab ====
@@ Line 46: / Line 45: @@
 === 2. Compile the Linux kernel ===
+<code bash>
+$ source ~/work/scripts/setenv.sh
+$ cd ~/work/nss-linux
+$ make tn_imx8_defconfig
+$ make -j8
+</code>
+Successful compilation will create the following binaries:
+  * ''arch/arm64/boot/Image'' - this is the resulting Linux kernel image
+  * ''arch/arm64/boot/dts/freescale/imx8mq-pico-pi.dtb'' - device tree blob files
+  * a set of Linux kernel modules (''*.ko'') scattered around the Linux kernel working tree.
+We also have prebuild binaries for ''Image'' and ''imx8mq-pico-pi.dtb'' found under  ''~/work/images/'' directory to be used as a backup.
 === 3. Boot the board ====
+Connect the PICO-PI-IMX8M to your laptop using the two USB cables provided as described on [[https://developer.technexion.com/docs/recover-to-factory-settings-pico-imx8m-mini | Technexion ]] webpage.
+{{:lkd:laboratoare:pico-pi-imx8m-mini-cables.jpg}}
+  - Yellow box: debug console cable
+  - Red box: power cable (USB Type C)
+  - Magent box: boot configuration jumper location.
+Make sure the board is in ''Serial Download Mode''. Jumper location should be set as follows:
+{{:lkd:laboratoare:pico-imx8m-pi-serial-download-mode.png}}.
+Now, we are ready to boot the board. Open two consoles:
+Console #1
+<code bash>
+$ minicom -D /dev/ttyUSB0
+</code>
+Console #2
+<code bash>
+# sudo ~/work/scripts/uuu ~/work/scripts/uuu_script
+</code>
+And then hit ''Reset'' button on the board.
+During the booting of the board you will need to tell Virtualbox which USB devices to passthrough the Guest Linux.
+{{:lkd:laboratoare:usb_filter.png}}
+The final consoles should look like this. Notice Console #1 has Linux kernel booting log:
+{{:lkd:laboratoare:boot_run.png?736x356}}
+<note important>Use user ''root'' and password ''root'' to login on Linux running on the board </note>
+=== 4. Make a change in the Linux kernel ===
+Go to the Linux kernel source root tree and modify a file.
+<code bash>
+$ cd ~/work/nss-linux
+$ vim ~/work/arch/arm64/kernel/setup.c
+</code>
+Add a simple print like in the following patch
+<code c>
+--- a/arch/arm64/kernel/setup.c
++++ b/arch/arm64/kernel/setup.c
+@@ -90,6 +90,8 @@ void __init smp_setup_processor_id(void)
+        pr_info("Booting Linux on physical CPU 0x%010lx [0x%08x]\n",
+                (unsigned long)mpidr, read_cpuid_id());
++
++       pr_info("Hello from Embedded Linux Summer School\n");
+ }
+</code>
+Now recompile the kernel. You can go back and read [[#compile_the_linux_kernel | 2. Compile the Linux kernel]]. Sequence for recompiling the kernel is as simple as:
+<code bash>
+$ cd ~/work/nss-linux
+$ source ~/work/scripts/setenv.sh
+$ make -j8
+</code>
+Boot script ''~/work/scripts/uuu_script'' will use your newly compiled Linux kernel image. So there is no need to change anything after your recompiled the kernel. Just follow again the steps in section  [[#boot_the_board |3. Boot the board ]]!
+Now, with the new boot image notice the new logs on the console:
+<code bash>
+[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034]
+[    0.000000] Hello from Embedded Linux Summer School
+[    0.000000] Linux version 6.1.55-ga5f70b9823b6-dirty (student@nss)
+[    0.000000] Machine model: TechNexion PICO-IMX8MQ and PI baseboard
+</code>
+=== 5. Make a change in the rootfs ===
+rootfs (or the root file system) is the filesystem that is mounted at ''/'' (root of the hierarchy) and contains all the files necessary for the operating system to boot and run.
+<code bash>
+# ls /
+bin         home        lost+found  proc        srv         var
+boot        lib         media       root        sys
+dev         lib64       mnt         run         tmp
+etc         linuxrc     opt         sbin        usr
+</code>
+In our setup, the rootfs used to boot the board can be found in ''~/work/images/rootfs.ext2''. Use the following instructions that add one of your own files into the root filesystem.
+<code bash>
+$ cd ~/work/images
+# make a backup of the initial root filesystem
+$ cp rootfs.ext2 rootfs.ext2.back
+$ sudo mkdir /mnt/my_root
+$ sudo mount -o loop rootfs.ext2 /mnt/my_root
+# explore the contents of /mnt/my_root directory and notice that these are the exact files that you can find on the board
+# create your own file
+$ sudo touch /mnt/my_root/root/my_file
+# unmount the filesystem
+$ sudo umount /mnt/my_root
+</code>
+Now boot the board and notice that the file you created exists on the board! Follow the steps in section  [[#boot_the_board |3. Boot the board ]]!
+=== 5. Explore the board ===
+After booting the board and getting the prompt explore the hardware board capabilities.
+Check the current Linux kernel version:
+<code bash>
+$ cat /proc/version
+</code>
+Check the command line arguments used to start the Linux kernel:
+<code bash>
+$ cat /proc/cmdline
+</code>
+List all the cpus in the system:
+<code bash>
+$ cat /proc/cpuinfo
+</code>
+List all available free and used physical memory in the system.
+<code bash>
+$ free -h
+</code>
+List the physical memory map for the system:
+<code bash>
+$ cat /proc/iomem
+</code>
+Notice the address range for ''System RAM'' and for the rest of devices.
+Check the current list of filesystems supported by the kernel:
+<code bash>
+$ cat /proc/filesystems
+</code>
+Check the current list of modules loaded in the system:
+<code bash>
+$ cat /proc/modules
+</code>
+Finally check the kernel log:
+<code bash>
+$ dmesg
+</code>

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