Linux Debug
Tips to do debugging under Linux.
Contents
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.
Unlock registers access
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Note: On APF51 & APF28 you don't have to explicitly unlock registers in U-Boot to access them under Linux, like explained just above |
- 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
Usage
- 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 or http://www.linuxtopia.org/online_books/linux_kernel/kernel_configuration/ch09s07.html
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 ....
