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Cortex-A9 RealMode Memory size

gael therond
Note: This was originally posted on 29th April 2011 at http://forums.arm.com

Dear ARM's guru,

I'm asking myself about the ARM real mode and especially about the memory management on this mode.

Is there a limitation on memory allocution in real-mode under ARM?
Is ARM's Cortex CPU behave like Intel's x86 CPU in real-mode in term of memory allocution?

In fact I want to know if I could use more than the usual 1Mb (Using Gate A20 trick) available in real-mode with an Intel CPU.

Many thanks in advance.
  • Note: This was originally posted on 30th April 2011 at http://forums.arm.com

    Many thanks to your answer sim!

    This is exactly the answer I was looking for ;)

    I'm currently trying to develop a fast bootloader for my NVidia TEGRA 250 DevKit and as NVidia doesn't provided us the TRM I was not sure about this point.

    More I use ARM Processors, more I like it, there are no limitation due to backward compatibility for now, and that a good point on it :D
  • Arm Employee Badge
    Note: This was originally posted on 30th April 2011 at http://forums.arm.com

    None of the concepts you mention exist in ARM systems.

    Out of reset the memory is 4GB linear and flat mapped; with the MMU enabled, each process still has a 4GB linear address space, however, the operating system can map each 4KB to any physical address.

    The answer to your final question appears to be yes, you can [theoretically] use ~4096 times the amount.

    hth
    s.