UM1535 datasheet(29/39 Pages) STMICROELECTRONICS

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UM1535

Working with customized kernels

Doc ID 023036 Rev 2

29/39

To configure the kernel using a default configuration (for example, for SPEAr1340), enter the

kernel source tree directory and run the commands:

$ make distclean

$ make ARCH=arm CROSS_COMPILE=armv7-linux- spear13xx_defconfig

To modify the default configuration, from the terminal run the make ARCH=arm

CROSS_COMPILE=armv7-linux- menuconfig tool in the kernel source tree root directory.

Now you can change all the configuration options.

Use the arrows keys to navigate in the menu structure and change the options. When all

changes are done, save the configuration and exit. The new configuration is saved in a

hidden ".config" file. If you like, you can choose another name.

6.2

Rebuilding the kernel

After the configuration step is finished, the kernel can be rebuilt with a "make" command:

$ make ARCH=arm CROSS_COMPILE=armv7-linux- uImage

If you configured some components as modules, you also need a make ARCH=arm

CROSS_COMPILE= armv7-linux- modules command afterwards.

The time required for the build process is varies depending on the number of features you

choose during the configuration step and your PC speed (usually it takes some minutes).

When the build process is completed, you can find the kernel images in the arch/arm/boot

subdirectory of the kernel tree, both as uncompressed (Image) and compressed (zImage,

uImage) kernel image.

6.3

Workflow models

The kernel binary image is always generated on the development PC. However, there are

many approaches (workflows) to make the kernel operating on the target evaluation board.

The main ones are described in the following subsections.

6.3.1

Booting the kernel on-demand

If the board can be connected to the development PC through an Ethernet LAN, one

solution is to load the kernel binary image file just after reset by configuring U-Boot for

automatic file transfer by TFTP protocol.

This approach is especially useful when frequently modifying the kernel, for instance during

adaptations to a device drivers that are statically linked with kernel code.

To enable TFTP support on the development PC, you must make sure that the TFTP

daemon program /usr/sbin/in.tftpd is installed. On Fedora Core systems you can verify this

by running:

$ rpm -q tftp-server

If necessary, install the TFTP daemon program from your distribution media.

Most Linux distributions disable the TFTP service by default. To enable it, for example on

Fedora systems, edit the file /etc/xinetd.d/tftp and remove the line

disable = yes

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