AM2432: details how memory configuration can be changed

Hi SL,

Regarding to the MPU settings, please refer to the following thread:

(+) AM2432: GPMC - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

Best regards,

Ming

Hi SI,

Sung-IL said:

Does 'MPU ARMv7' mean 'R5' Core in below sysconfig?

Yes, this is the MPU configuration for the R5F.

Sung-IL said:

it would be very helpful if there is other document for memory configuration and modification

I'll see if we can improve the FAQ you mentioned.

The options provided in Sysconfig map directly to the MPU configuration options described in ARM documentation.

For "Region Attributes", please note "Advanced Configuration" allows setting the TEX bits exactly as desired.

Also note hovering over some options results in pop-up text with some details on the option.

For the ARM docs, please see:

• ARM Cortex-R Series Programmer's Guide: https://developer.arm.com/documentation/den0042/a/The-Memory-Protection-Unit
• Cortex-R5 Technical Reference Manual: https://developer.arm.com/documentation/ddi0460/d/Memory-Protection-Unit
• ARM Architecture Reference Manual, ARMv7-A and ARMv7-R edition: developer.arm.com/.../latest, Section B.5 Protected Memory System Architecture (PMSA)

Regards,
Frank

Hi SI,

Sung-IL said:

'Supervisor' should be OS or FW, and 'User mode' should be in application SW, right?

Yes, your understanding is correct. Please see: https://developer.arm.com/documentation/ddi0460/d/Programmers-Model/Modes-of-operation-and-execution/Modes-of-operation?lang=en. In Sysconfig, it would be better to use 'Privileged' instead of 'Supervisor' since the setting applies to all execution modes except User (USR) mode.

Sung-IL said:

'User RD' mean application SW can only read from TCM and can't write into TCM, right?

It means any code executed while the CPU is in USR mode can't write to TCM.

Sung-IL said:

Why TCM is set to "Supervisor RD+WR, User RD"?

Please see the SDK startup code here: source/kernel/nortos/dpl/r5/boot_armv7r_asm.S:89:_c_int00:

I notice the startup code sets the CPU to System (SYS) mode before the call to __mpu_init. The CPU is left in SYS mode even after calling main(). Setting aside IRQ, FIQ, etc., SDK code executes in SYS mode and doesn't enter USR mode.

I don't know why "User RD" is the default setting for the SDK. It could just as well be "User BLOCK" and SDK code will execute correctly. I'll ask the SW Development team about this and let you know what I find.

Developers using the SDK can add code to place the CPU in USR mode. In this case, the "User Read" setting might come into play (e.g. if the new code in USR mode attempts to write to an MPU region set for "User Read").

Regards,
Frank

Hi SI,

I got this additional feedback from the SW Development team:

User mode execution is not supported in MCU+SDK . All tasks are executed only in supervisor mode in MCU+SDK and it never switches to user mode. The setting to mark  TCM as supervisor RD+WR would make sense if  we want to place kernel data structures in TCM and prevent unprivileged code from overwriting. However as we don’t support transition from user to supervisor mode I cant think of any logical reason for MPU to have such a configuration. Basically all USER access permission in MPU should be disregarded as user mode is not validated in MCU+SDK.

Regards,
Frank