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TMS570LC4357: QS on MPU: What difference between Arm assembly and C in MPU function?

li xy
Intellectual 355 points
Part Number: TMS570LC4357

Hi all:

    I  am the first time to use ARM assembly and MPU function. In my mind, If I need configure the MPU function, I will set mpu registers in lc4357 datasheet rather than arm assembly.

    In our product, I find that any use or configuration of MPU is realized through arm assembly rather than C.    

    My questions are :

    1. what are differences between assembly and C during configuration of MPU?

    2. Is that necessary to use assembly?

    3. what's the difference between the PSMA regsister "DRBAR" and MPU register "MPUREGBASE"?

Best Wish

Li

  • 0
    TI__Guru**** 192666 points

    Hi Li,

    The MPU is configured through CP15 registers using ARM MCR and MRC instructions like enabling MPU with the following code:

    MRC p15, 0, R1, c1, c0, 0

    ; read CP15 register 1

    ORR R1, R1, #0x1

    DSB

    MCR p15, 0, R1, c1, c0, 0 ; enable MPU

    ISB

    li xy said:
        2. Is that necessary to use assembly?

    Yes, assembly code is used to config MPU

    li xy said:
      3. what's the difference between the PSMA regsister "DRBAR" and MPU register "MPUREGBASE"?

    I don't know PSMA, DRBAR, and MPUREGBASE registers. Can you tell me where you get those names?

    Please refer to ARM TRM: https://developer.arm.com/documentation/ddi0460/d/Memory-Protection-Unit

  • 0 in reply to QJ Wang
    Intellectual 355 points

    Hi QJ:

    For Q1, I think MPU could be configured through C code instead of arm assembly. is that right?

    For Q3, the  DRBAR is register of PMSA and they are from "ARM® Architecture Reference Manual ARMv7-A and ARMv7-R edition" ,Section B6.1.36, page 1840;

    The DRBAR is Data Region Base Address Register. PMAS is protected memory system architecture.

    Here is the example in assembly:

    To access the DRBAR, software reads or writes the CP15 registers with <opc1> set to 0, <CRn> set to c6, <CRm> set to
    c1, and <opc2> set to 0. For example:
    MRC p15, 0, <Rt>, c6, c1, 0 ; Read DRBAR into Rt
    MCR p15, 0, <Rt>, c6, c1, 0 ; Write Rt to DRBAR

    And in our product, here is the code:

    //=====================================================================
    // Init helper
    // mpuInitRegion
    //=====================================================================
        .global     mpuInitRegion
        .type       mpuInitRegion, function
        .func       mpuInitRegion
        .thumb_func
    mpuInitRegion:  // only for init!
        mov   ip, #0                               // To disable region before manipulation
        mcr    p15, #0, r0, c6, c2, #0     // RGNR, MPU Region Number Register
        mcr    p15, #0, ip, c6, c1, #2     // DRSR, Data Region Size and Enable Register
        mcr    p15, #0, r1, c6, c1, #0    // DRBAR, Data Region Base Address Register
        mcr    p15, #0, r3, c6, c1, #4    // DRACR, Data Region Access Control Register
        mcr    p15, #0, r2, c6, c1, #2    // DRSR, Data Region Size and Enable Register
        bx    lr
        .endfunc
    //=====================================================================

    I think the code above is that DRBAR register is same as the of "MPUREGBASE" register.