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Self Modifying Code on the ARM1176JZF-S (raspberry pi)

Sally Chak
Note: This was originally posted on 6th April 2013 at http://forums.arm.com

Hello
I'm trying to write some Self modifying code (SMC) to run on my raspberry pi and I've been reading a few things and am slightly confused.
  • [size=2]From what I understand, ARMv6-M is thumb2 only (i.e. always in thumb mode)  So if I want to write SMC, it has to be in thumb 2? (despite the 1176JZF-S? being able to run both arm and thumb?)
    [/size]
  • [size=2]Should I use MCRR (and stay in the assembly) or linux's mmap/mprotect/__cache__clear (in the OS) for cache coherence?

    Currently, I just keep getting segmentation faults on my code


    Best
    Sally[/size]
  • Note: This was originally posted on 7th April 2013 at http://forums.arm.com


    ARMv6-M is Thumb only.  However, the ARM1176JZF-S is an implementation of ARMv6 with the Security Extensions - not - ARMv6-M.  I know this can be somewhat confusing.  Basically ARMv6-M and ARMv7-M are the versions of the architecture of used by the Cortex-M microcontrollers.
    For the record, the ARM1176JZF-S does NOT support Thumb-2. It supports ARM and Thumb (or Thumb-1 if that's clearer).
    My Linux experience is admittedly limited, but I'd recommend use the kernel calls.  It will help make your code more portable, and is why they're provided in the first place.




    Oh No... I've been assuming I've been in thumb mode all the time.
    Ok, thanks then.

    Do people also happene to know what machine code instruction to use to switch between ARM mode and thumb mode?
  • Note: This was originally posted on 8th April 2013 at http://forums.arm.com

    Got it. Thanks!
  • Arm Employee Badge
    Note: This was originally posted on 7th April 2013 at http://forums.arm.com

    ARMv6-M is Thumb only.  However, the ARM1176JZF-S is an implementation of ARMv6 with the Security Extensions - not - ARMv6-M.  I know this can be somewhat confusing.  Basically ARMv6-M and ARMv7-M are the versions of the architecture of used by the Cortex-M microcontrollers.
    For the record, the ARM1176JZF-S does NOT support Thumb-2. It supports ARM and Thumb (or Thumb-1 if that's clearer).
    My Linux experience is admittedly limited, but I'd recommend use the kernel calls.  It will help make your code more portable, and is why they're provided in the first place.

  • Arm Employee Badge
    Note: This was originally posted on 7th April 2013 at http://forums.arm.com

    In v6; BX, BLX or a load with the pc as the destination
    The "BLX " instructions always causes a state change.
    For the "BX Rd" and "BLX Rd" instructions, and loads to the PC, the bottom bit of the value written to the PC controls the state you arrive in.