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TMS570LS3137: Unexpected HALcoGen MPU Background Region Enable Function Behaviour

Tyler Bailey
Prodigy 20 points
Part Number: TMS570LS3137
Other Parts Discussed in Thread: HALCOGEN,

Tool/software:

I've been experimenting with the MPU background region and have noticed that calling HALcoGen's _mpuEnableBackgroundRegion_() function from sys_mpu.asm seems to perform the opposite operation compared to what I'm expecting and disables the background region. As detailed in the ARMv7-A/ARMv7-R reference manual, "When the SCTLR.BR bit is set to 0, the MPU behaves as if there is a background region that generates a Background fault memory abort on any access."

The _mpuEnableBackgroundRegion_() function sets the SCTLR.BR bit to 1 via "orr   r0,  r0, #0x20000". When performing a read or write to a memory address which does not correspond to a configured MPU region and does not generate a data abort by default as defined in table 6.9.2 within the TMS570LS3137 datasheet (e.g: 0x80000000), no data abort is generated. When removing the call to _mpuEnableBackgroundRegion_() (i.e: SCTLR.BR is 0), a data abort is generated.

Just want to confirm whether or not this behaviour is expected and my understanding is backwards, or if HALcoGen's "Enable" and "Disable" terminology in this case is backwards in reference to the ARM reference manual.

Thanks!

  • 0
    TI__Guru 63035 points

    Hi Tyler Bailey,

    Is it possible to share your project to re-create the issue at my end?

    --
    Thanks & regards,
    Jagadish.

  • 0 in reply to jagadish gundavarapu
    Prodigy 20 points

    Hi Jagadish,

    My apologies for the late reply. Unfortuntately, I'm unable to share the full project, however here are the details necessary to recreate the issue:

    1. Create a HALcoGen project for the TMS570LS3137 with FreeRTOS.
    2. Within os_port.c, make the changes detailed below to perform a read from the EMIF CS0 region with the MPU background region enabled using the HALcoGen provided MPU functions within sys_mpu.h:
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        static void prvSetupDefaultMPU( void )
        {
        /* make sure MPU is disabled */
        prvMpuDisable();
        /* First setup the entire flash for unprivileged read only access. */
        prvMpuSetRegion(portUNPRIVILEGED_FLASH_REGION, 0x00000000, portMPU_SIZE_4MB | portMPU_REGION_ENABLE, portMPU_PRIV_RO_USER_RO_EXEC | portMPU_NORMAL_OIWTNOWA_SHARED);
        /* Setup the first 32K for privileged only access. This is where the kernel code is
        placed. */
        prvMpuSetRegion(portPRIVILEGED_FLASH_REGION, 0x00000000, portMPU_SIZE_32KB | portMPU_REGION_ENABLE, portMPU_PRIV_RO_USER_NA_EXEC | portMPU_NORMAL_OIWTNOWA_SHARED);
        /* Setup the the entire RAM region for privileged read-write and unprivileged read only access */
        prvMpuSetRegion(portPRIVILEGED_RAM_REGION, 0x08000000, portMPU_SIZE_512KB | portMPU_REGION_ENABLE, portMPU_PRIV_RW_USER_RO_EXEC | portMPU_NORMAL_OIWTNOWA_SHARED);
        /* Default peripherals setup */
        prvMpuSetRegion(portGENERAL_PERIPHERALS_REGION, 0xF0000000,
        portMPU_SIZE_256MB | portMPU_REGION_ENABLE | portMPU_SUBREGION_1_DISABLE | portMPU_SUBREGION_2_DISABLE | portMPU_SUBREGION_3_DISABLE | portMPU_SUBREGION_4_DISABLE,
        portMPU_PRIV_RW_USER_RW_NOEXEC | portMPU_DEVICE_NONSHAREABLE);
        /* Privilege System Region setup */
        XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
    3. When debugging the modified code in CCS, add a breakpoint on the line which performs a read from EMIF memory. When stepping over this breakpoint, no data abort occurs.
    4. Now, to perform a test of the case where the MPU background region is disabled, modify the prvSetupDefaultMPU() function as follows:
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        static void prvSetupDefaultMPU( void )
        {
        /* make sure MPU is disabled */
        prvMpuDisable();
        /* First setup the entire flash for unprivileged read only access. */
        prvMpuSetRegion(portUNPRIVILEGED_FLASH_REGION, 0x00000000, portMPU_SIZE_4MB | portMPU_REGION_ENABLE, portMPU_PRIV_RO_USER_RO_EXEC | portMPU_NORMAL_OIWTNOWA_SHARED);
        /* Setup the first 32K for privileged only access. This is where the kernel code is
        placed. */
        prvMpuSetRegion(portPRIVILEGED_FLASH_REGION, 0x00000000, portMPU_SIZE_32KB | portMPU_REGION_ENABLE, portMPU_PRIV_RO_USER_NA_EXEC | portMPU_NORMAL_OIWTNOWA_SHARED);
        /* Setup the the entire RAM region for privileged read-write and unprivileged read only access */
        prvMpuSetRegion(portPRIVILEGED_RAM_REGION, 0x08000000, portMPU_SIZE_512KB | portMPU_REGION_ENABLE, portMPU_PRIV_RW_USER_RO_EXEC | portMPU_NORMAL_OIWTNOWA_SHARED);
        /* Default peripherals setup */
        prvMpuSetRegion(portGENERAL_PERIPHERALS_REGION, 0xF0000000,
        portMPU_SIZE_256MB | portMPU_REGION_ENABLE | portMPU_SUBREGION_1_DISABLE | portMPU_SUBREGION_2_DISABLE | portMPU_SUBREGION_3_DISABLE | portMPU_SUBREGION_4_DISABLE,
        portMPU_PRIV_RW_USER_RW_NOEXEC | portMPU_DEVICE_NONSHAREABLE);
        /* Privilege System Region setup */
        XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
    5. When debugging the modified code in CCS, again add a breakpoint on the line which performs a read from EMIF memory. When stepping over this breakpoint, a data abort occurs.

    These results illustrate the inverted behaviour I've described - when the MPU background region is "enabled", no data abort occurs - this is the opposite of what I'm expecting given the details provided about the TMS570LS3137's Cortex-R4F MPU.

    Thanks,

    Tyler

  • 0 in reply to Tyler Bailey
    TI__Guru 63035 points

    Hi Tyler,

    Thanks for your code, i will go through it and i will try to provide my updates as soon as possible.

    --
    Thanks & regards,
    Jagadish.

  • 0 in reply to jagadish gundavarapu
    TI__Guru 63035 points

    Hi Tyler,

    Apologies for the delay in late response, i was stuck with other issues in this mean time.

    I found something:

    I think you should need to disable the region-1 to test the Background region enable check:

    Please refer below highlighted sentences in the core reference manual:

    Can you please once again test the behavior of BR bit by disabling the region-1 once.

    --
    Thanks & regards,
    Jagadish.