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bit addressable arrays in ARM9

sgupta sgupta
Note: This was originally posted on 5th January 2009 at http://forums.arm.com

plz help me by telling hw we can use bit addressable arrays menas arrays that can be used bitwise..while programming through keil microvision , is there any option available??? plz help..
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  • 0 Arm Employee Badge
    Note: This was originally posted on 6th January 2009 at http://forums.arm.com

    ARM has no "access per bit" instruction - so the compiler will need to acccess bytes and then extract the data it needs using shifts / masks. While you could use language extensions to do this, writing it yourself shouldn't be too hard.

    That said... Cortex-M3 is a special case which supports a bit-banded memory region (each bit is addressable as one word in the address map, removing the need for the mask and shift). There is a 32MB bit-band memory allocated in the address map, which allows addressing of a 1MB array of memory.

    It depends on the MCU implementation on how much of this bit-band is allocated to real memory.

    Cheers,

    Iso
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  • 0 Arm Employee Badge
    Note: This was originally posted on 6th January 2009 at http://forums.arm.com

    ARM has no "access per bit" instruction - so the compiler will need to acccess bytes and then extract the data it needs using shifts / masks. While you could use language extensions to do this, writing it yourself shouldn't be too hard.

    That said... Cortex-M3 is a special case which supports a bit-banded memory region (each bit is addressable as one word in the address map, removing the need for the mask and shift). There is a 32MB bit-band memory allocated in the address map, which allows addressing of a 1MB array of memory.

    It depends on the MCU implementation on how much of this bit-band is allocated to real memory.

    Cheers,

    Iso
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