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Original question:

MCU-PLUS-SDK-AM243X: MMR write protection mechanisms

MCU-PLUS-SDK-AM243X: Safety Diagnosis，MMR-F3:MMR write protection mechanisms

Jimmy
Prodigy 170 points
Part Number: MCU-PLUS-SDK-AM243X
Other Parts Discussed in Thread: AM2432

Tool/software:

Hello Expert,

We have conducted further research on the MMR-F3: MMR write protection mechanisms diagnostic procedure and have come across some doubts.

According to the response from your previous post, this diagnostic procedure does not require software-based operations. However, in the safety manual, it explains that this diagnostic procedure is related to the Proxy1 address, whereas TI's example code does not use the Proxy1 address mentioned in the explanation. We are wondering if there is a need for implementing the diagnostic measure using the Proxy1 address in software and whether there is any reference code available.

Please refer to the following manual contentAM64x,< AM243x Functional Safety Manual>:

6.3.107 MMR write protection mechanisms
This MMR module has Proxy Addressing enabled. Each of the following register descriptions lists the Proxy0 address offset which is intended as the normal read/write access address. A second Proxy1 address also exists to provide exclusive register write control to safety-aware processing elements. When the associated claim register bit is set, a register becomes read-only at its Proxy0 address and may only be written through its Proxy1 address. Claim registers themselves are always readable through their Proxy0 address but may only be written through their Proxy1 address.

Thank you
Best regards

Jimmy

  • 0
    TI__Mastermind 18357 points

    Hello Jimmy,

    Jimmy said:
    whether there is any reference code available

    Currently, there is no reference example available in SDL for this.

    Jimmy said:
    if there is a need for implementing the diagnostic measure using the Proxy1 address in software

    I am forwarding this thread to a safety expert to comment on this.

    Regards,
    Krithika

  • 0 in reply to Krithika Ravi
    Prodigy 170 points

    Hello Krithika

    Thank you for your response, looking forward to the expert's reply.

    Thank you
    Best regards

    Jimmy

  • 0 in reply to Jimmy
    TI__Guru 68760 points

    Hi Jimmy, 

    The Proxy mechanism being referred to in MMR-F3 is similar to the Firewall mechanism that is described in 4.4 Device Configuration.

    There is a diagnostic for firewalls CBA-8.

    I would have expected a similar diagnostic for MMR Proxy as this is an extension of firewall but can economically map each individual MMR to one of two addresses, separated by 4K, so that register by register select register can be pushed to an address (for write access) that is either within a firewall protected region or out of the region.  

    MMR-F3 is not 'written up' as a diagnostic, it is a mechanism.  But it works like a firewall extension and I would think it would be covered with a diagnostic similar to CBA-8.   I'll need to research why this isn't the case, but hopefully this helps explain what the item is referring to.

    Note that you can use firewalls without proxy.  If you can simply map all registers within a partition to one CPU and use a firewall to protect the entire partition then no need to use the Proxy.   The proxy is only needed if you need to split ownership of MMRs within the same partition.   

  • 0 in reply to Anthony F. Seely
    Prodigy 170 points

    Hi Anthony

    Thank you for your response. Your reply has been very helpful to us, and now I have a more comprehensive understanding of MMR-F3.

    In our application scenario, we only use one R5 core of the AM2432, without any kernel interactions. Hence, we didn't use a firewall in this situation. Under these circumstances, can we also avoid using a proxy?

    Thank you
    Best regards

    Jimmy

  • +1 in reply to Jimmy
    TI__Guru 68760 points

    In my opinion yes.  What I would say is if you think you need to use firewalls, then also consider the proxy feature as an extension of firewalls.

  • 0 in reply to Anthony F. Seely
    Prodigy 170 points

    Hi Anthony

    Thank you for your reply, I already have the answer, it's very helpful to us.


    Thank you
    Best regards

    Jimmy