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MSP430FR5994: Hardware Multiplier thread security issue

Yale Li 李耀先
Expert 4660 points

Part Number: MSP430FR5994

Hi Team,

Is there any thread security issue when using Hardware Multiplier with RTOS?

Thanks & Regards,

Yale Li

  • 0
    TI__Genius 10060 points

    Hi Yale,

    Can you help me understand what "thread security" means in your question? MSPM0 has a couple features that may be related:

    • M0 has two execution modes: handler and thread. Handler has full access to the system. Thread can be restricted. 
    • Memory protection unit can restrict access to regions of memory to privileged code.
    • MSPM0 has a single cycle HW multiply

    Hope that help. I'm interested to hear more about your question.

    Regards,

    Evan

  • 0 in reply to Evan Lew
    TI__Expert 4660 points

    Hi Evan,

    Thanks for your reply.

    This customer is using RTOS, so the thread mentioned above refer to the thread module like task, software interrupt and hardware interrupt etc. I'm not familiar with RTOS. It seems related to some stability issue of OS software.

    And the customer is using FR5994, not M0.

    Thanks & Regards,

    Yale Li

  • 0 in reply to Yale Li 李耀先
    TI__Genius 10060 points
    Yale Li 李耀先 said:
    And the customer is using FR5994, not M0.

    Ok, thanks for pointing that out. I missed that.

    I'm not sure what the customer is wanting to know. Can you ask about what security/threat-model the customer is trying to protect?

    Regards,

    Evan

  • +1
    Guru 25485 points

    An RTOS typically will not save the multiplier state which means that if multiple tasks use the multiplier, they must protect those operations by preventing a task switch. The usual thing to do is to disable interrupts during the operation. That can be tricky since sometimes the compiler will use it without an explicit multiply operator being visible.

    I looked up the description for the -mhwmult option for GCC and found:

       "The hardware multiply routines disable interrupts whilst running
         and restore the previous interrupt state when they finish.  This
         makes them safe to use inside interrupt handlers as well as in
         normal code."

    So GCC generated code should be OK. Other compilers may vary.

    If you access the multiplier directly, say to run an extended multiply accumulate operation, you are responsible for protecting it.

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