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Problem with CPU Data cache

virupax virupax
Note: This was originally posted on 15th December 2009 at http://forums.arm.com

Hi
I am using arm926ej-S processor and using the linux 2.6.27 kernel. If i enable the cpu DCACHE then the kernel is not booting up.
Can some one tell me is this because of some issue with the processor. I am using at91sam9g20 controller.
Is there some test application or test method which can be used to test internal data cache of the processor,  to check is there is some problem with the processor's internal data cache.

Thanks

Virupax
  • Note: This was originally posted on 16th December 2009 at http://forums.arm.com

    sim

    Thank you for the reply.

    I am disabling the data cache in the kernel source code where it is getting enabled, in other words i am changing the kernel source code not to enable the data cache.
    There are two places(which i have found) in the linux kernel source code where the data cache is being enabled.
    1) The "arch/arm/boot/compressed/head.S" which is used for decompressing the kernel and here i have changed the code manually to not to enable the data cache.
    writing #0x0009 instead of #0x000d to the c1 register of the cp15.
    2) The "arch/arm/kernel/head.S" file and for this the CONFIG_CPU_DCACHE_DISABLE kernel config option is sufficient to disable the data cache enabling.

    If i dont do the first one , i get
    Uncompressing Linux.............................................................
    ................................................
    crc error
    -- System halted

    and if the first change is done and the seconds one is not done, then the kernel boots up but fails to mount the RFS. On doing both  changes the kernel boots up fine with the RFS.

    I feel like data chache disabling is needed only at places where there is some king of data decompression is there.
    I am seeing this issue on only one board. I have several other boards on which the kernel works fine.
    I am not been able to make the issue is because of the bad controller(9G20) or Processor ( arm926ej-S) or the peripherals connected to the controller( like SDRAM).

    Any ideas will be helpful.

    Thanks
  • Arm Employee Badge
    Note: This was originally posted on 15th December 2009 at http://forums.arm.com

    It's not clear whether you are enabling the cache within the Linux build, or before entering the kernel.
    Either way, it's probably worth reading [url="http://www.arm.linux.org.uk/developer/booting.php"]http://www.arm.linux.org.uk/developer/booting.php[/url]

    hth
    s.