• State Accepted Answer
  • +1 person also asked this people also asked this
  • Locked Locked
  • Replies 5 replies
  • Subscribers 345 subscribers
  • Views 9781 views
  • Users 0 members are here
Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Is ARMv7-M3 thumb instructions compatible to ARMv7-A thumb?

Kaiyuan

Hello guys,

I am trying to verify some features of ARMv7-M3 in a software simulator platform for ARM. But this simulator only support ARMv7-A ISA.

Is ARMv7-M3 instructions compatible to ARMv7-A, especially thumb instructions?

Thank you very much.

  • 0

    Hi,

    according to the Cortex-A5/A7/A8/A9/A17 TRMs, these processors support Thumb encoding after the introduction of Thumb-2 technology, and for all 16-bit and 32-bit Thumb basic instructions.

    This means existing ARMv7-A processors support Cortex-M3 ISA because it is the Thumb-2.

    However, I don't know whether Cortex-M3 has Non-basic Thumb-2 instructions.

    Best regards,

    Yasuhiko Koumoto.

  • 0

    The Cortex-M3 doesn't have the DSP or floating point instructions. The ARMv7-A doesn't support all the Cortex-M system things in particular how interrupts are handled or the bit-banding. I believe you should be able to run M3 programs on an ARMv7-A emulator if you don't need to use those system facilities and you should use build flags to exclude the DSP and floating point options.

    Also see Free ARM Cortex-M3 Simulation Software?

  • 0

    Hi Kaiyuan,

    Another feature of ARMv7-A not present in Cortex-M3 (ARMv7-M) is NEON Advanced SIMD extension. While it is only an optional extension to the architecture, majority of Cortex-A devices implement it. Although you are in the opposite circumstance (simulating Cortex-M3 instructions in ARMv7-A simulator), this difference could be a cause of confusion. Replacing your simulator with one that specifically supports Cortex-M3 is a good idea. You can try those mentioned in the link in daith's reply.

    Regards,

    Goodwin

  • +1

    You might find this diagram useful.

    Cortex-M Instruction Sets.png

    This shows the different subsets of the Thumb instruction set which are supported by the different members of the Cortex-M family. The smallest subset is support by Cortex-M0 and the largest by Cortex-M4 with FPU extensions. The width of each box shows the size of each instruction - small boxes are 16-bit instructions and large ones are 32-bit.

    Hope this helps.

    Chris

  • 0

    Dear Kaiyuan,

    Cortex-M3 instructions are a subset of arm-v7m instructions. arm-v7m instruction is application level compatiable with arm-v7a. So the following system instrctions are different in cortex-m3: CPS, MRS, MSR.

    All other instructions are compatiable with ARM-V7A.