Difference between revisions of "Linux Debug"

Revision as of 20:27, 1 August 2010

Tips to do debugging under Linux.

Introduction

On this page, you will find usefull informations for debugging your Linux kernel/drivers.

Testing your custom Linux kernel before flashing it

You can test a linux kernel you've generated without having to reflash your board and destroy your currently working image. Indeed Linux kernel images can be loaded and started from SDRAM with U-Boot:

 BIOS> tftp ${loadaddr} ${board_name}-linux.bin
 BIOS> bootm ${loadaddr}

Changing processor registers from Linux user space with imxregs

This tool allows you to access i.MX registers from Linux userspace/console. This way you can debug your driver or access i.MX hardware functionnalities directly from Linux console.

In recent releases (>= 3.0) you should find this tool in /usr/bin/ on your board.

• To use it, you must clear i.MX PAR_1 & PAR_2 registers (registers access rights) before launching Linux kernel, so in U-Boot type (example here is for APF9328):

 BIOS> mw.l 0x00200008 0
 BIOS> mw.l 0x00210008 0

• on APF27:

 BIOS> mw 10000008 0
 BIOS> mw 10020008 0

If you use it frequently, a small script unlock_regs has been defined in U-Boot, and you can call it before booting your board:

 BIOS> run unlock_regs
 BIOS> boot

• Then in Linux console/terminal, launch imxregs like that:

 # imxregs REGISTER_NAME    (give it the register name as printed in i.MX Ref Manual or just the begining of the name)

or

 # imxregs    (to dump all supported registers)

Examples:

• Show OCR1 registers of each GPIO Port:

 # imxregs OCR1

• Write 0x00000123 to OCR1_D register:

 # imxregs OCR1_D 123

Changing FPGA IP's registers from Linux user space with fpgaregs

see FPGA_register

Using DebugFS

DebugFS is a in-kernel filesystem, similar to procfs or sysfs, that allows Linux driver to easily communicate debug informations to user space. Full documentation: http://lxr.linux.no/linux+v2.6.32/Documentation/filesystems/debugfs.txt

Mounting it

# mount -t debugfs none /sys/kernel/debug

Showing already allocated GPIOs

# cat /sys/kernel/debug/gpio
GPIOs 0-31, gpio-0:          
 gpio-5   (LCD                 ) in  lo
 gpio-6   (LCD                 ) in  lo
 gpio-7   (LCD                 ) in  lo
 gpio-8   (LCD                 ) in  lo
....

Links

• http://www-users.cs.umn.edu/~boutcher/kprobes/
• http://tree.celinuxforum.org/CelfPubWiki/PatchArchive