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load image into cache and execute it in cache

yitian bu
Note: This was originally posted on 31st January 2013 at http://forums.arm.com

Hi Experts:

    i have heard that some ARM platform providers load their bootloader into L2 cache, and execute the bootloader in L2 cache directly.

    how can this work? do they add some logic inside silicon to make this work?

    as my understanding, cache has differnt architecture from normal sram, how can CPU recognize the L2 cache as a normal sram and execute image in it directly?



Best Regards
Parents
  • Note: This was originally posted on 5th February 2013 at http://forums.arm.com


    I don't think that's going to work. If you use the CPU to do the copy of the second boot loader it is simply going to overwrite the first level bootloader. Locking things down in the cache does not make them immutable, nor change the fact that both bits of code exist at the same address =)

    Footnote - most devices have a small SRAM on chip for doing precisely what you are doing so you have some scratch RAM before main memory is available.

    Iso


    I agree, this is proved as standard practice to use any device local SRAM to use for booting before you configure DRAM (provided your ARM processor doesn't have local SRAM or ITCM). Otherwise ARM processor ITCM would suffice to get into the similar solution space. Another point to worth consider that few ARM processors require cache to be invalidated/cleared on reset.

         Vaibhav

Reply
  • Note: This was originally posted on 5th February 2013 at http://forums.arm.com


    I don't think that's going to work. If you use the CPU to do the copy of the second boot loader it is simply going to overwrite the first level bootloader. Locking things down in the cache does not make them immutable, nor change the fact that both bits of code exist at the same address =)

    Footnote - most devices have a small SRAM on chip for doing precisely what you are doing so you have some scratch RAM before main memory is available.

    Iso


    I agree, this is proved as standard practice to use any device local SRAM to use for booting before you configure DRAM (provided your ARM processor doesn't have local SRAM or ITCM). Otherwise ARM processor ITCM would suffice to get into the similar solution space. Another point to worth consider that few ARM processors require cache to be invalidated/cleared on reset.

         Vaibhav

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