Linux Debug

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 debug your driver or access i.MX hardware functionnalities directly from Linux console.

• First, you have to enable this tool in Buildroot (package selection for target -> Hardware handling / blockdevices and filesystem maintenance -> imxregs):

 $ make menuconfig

Once done, compile it:

 $ make

The generated file is located in $ARMADEUS_ROOTFS_DIR/usr/bin/. You can copy it directly on your target or reflash your rootfs.

• 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

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

 BIOS> run unlock_regs

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

 # imxregs REGISTER_NAME  (give it the register name as printed in iMX 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

Links

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

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