Linux Kernel Programming

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Linux Kernel Developing

U-boot and Kernel Compilation

1. Get right toolchain for your platform.

            a. Ubuntu: sudo apt-get install gcc-arm-linux-gnueabi/gcc-arm-linux-gnueabihf

or

           b.  Get from linaro.org : wget -c https://releases.linaro.org/14.04/components/toolchain/binaries/gcc-linaro-arm-linux-gnueabihf-4.8-2...

   2. Get U-boot code source

1. git clone http://git.denx.de/u-boot-imx.git
2. make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- wandboard_quad_config
3. make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-

   3. Get Kernel source with Wandboard support

1. Wandboard repo:
   1. git clone https://github.com/wandboard-org/linux.git
   2. Select the right branch:
   3. git checkout wandboard_imx_3.10.17_1.0.0_beta    

                              or     

                           git checkout wandboard_imx_3.0.35_4.1.0

             b. Kernel Configuration ( load the wandboard  config )

                     make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- wandboard_defconfig

                                    or

                           make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- menuconfig

             c. Kernel Compilation

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-

     4. Prepare the sdcard:

            I. Copy the u-boot on the sdcard

1. Determine the sdcard device name : sudo df -h
2. sudo umount /dev/sdd*
3. sudo dd if=/<path>/u-boot.imx of=/dev/sdd bs=512 seek=2

          II. Partitionating the sdcard

• sudo fdisk /dev/sdd
  • o
  • n
  • p
  • 1
  • 2048
  • +1G
  • t
  • c
  • n
  • p
  • 2
  • 12288
  • +5G
  •   P
• sudo mkfs.vfat -n KERNEL /dev/sdd1
• sudo mkfs.ext3 -L RFS /dev/sdd2
• cd /media/
• sudo mkdir KERNEL
• sudo mkdir RFS
• sudo mount /dev/sdd1 KERNEL/
• v. sudo mount /dev/sdd2 RFS/

         |||. Download a RFS and put on the sdcard

• wget -c https://rcn-ee.net/deb/minfs/wheezy/debian-7.5-minimal-armhf-2014-07-07.tar.xz
• sudo tar -xvf debian-7.5-minimal-armhf-2014-07-07.tar.xz  -C RFS/
• Put the dtb file and zImage on the sdcard ( KERNEL partition ).
• sudo cp <kernel_path>/arch/arm/boot/uImage /media/KERNEL
• sudo cp <kernel_path>/arch/arm/boot/imx6q_wandboard.dtb /media/KERNEL

IV. Setup the u-boot:

• run loadimage
• run loadfdt
• setenv bootargs console=ttymxc0,115200 root=/dev/mmcblk0p2 rootwait rw
• bootz ${loadaddr} - ${fdt_addr}

Kernel devices

Realise a kernel device controlled from user space. The following steps will be done on the virtual machine.

NEEDED: Get the Virtual Box softwarte:  https://www.virtualbox.org/wiki/Downloads

1. Realize a kernel device which prints “Hello World” starting from you’re the attached code.

   a . First determine the kernel version from target platform:

• uname –a
• Get the kernel sources or kernel headers using one of the following methods. On the current virtual machine this step is already done.
  • For kernel headers: sudo apt-get install linux-headers-$(uname -r)
  • For kernel sources:
    • sudo apt-get install linux-source

   b. Now go to the directory tasks/kernel. Create a function void hello() which prints “Hello World”.  It should be called when the device is inserted.

   c.  Compile the module : make

   d.  Insert the module on the virtual machine : insmod lec_cdev.ko

   e.  See if the module  is inserted

• lsmod
• dmesg

   f. Remove the kernel module :  rmmod lec_cdev.ko

   2. Create the device lec_cdev using  mknod  /dev/lec_cdev c 243 0

   3. Implement the read function of the device in order to have the following effect:

1. cat /dev/lec_cdev =>  print to infinit “a”
2. Modify the previous module in order to be commanded using ioctl from userspace.
   1. In function lec_cdev_ioctl  detect the command sent  from userspace and

If command is

• MY_IOCTL_HELLO prints “HELLO WORLD”;
• MY_IOCTL_SET_BUFFER – prints the buffer received from userspace.
• MY_IOCTL_GET_BUFFER – prints the data from the char device driver buffer

        HINT: use functions 

* copy_to_user(user_buffer, kernel_buffer, size)

* copy_from_user(kernel_buffer, user_buffer , size)