topic Re: LPC55S69: Boot-Rom area attributes in LPC Microcontrollers

LPC55S69: Boot-Rom area attributes

EugeneHiihtaja — Thu, 18 Jun 2020 11:17:35 GMT

Hi !

I have active MPU on secure side and run out of section for cover all specific areas.

What kind of default memory attributes has Boot-Rom area. MPU cover it with privileged access right.

But typical executable area have the next memory attributes:

portMPU_NORMAL_MEMORY_BUFFERABLE_CACHEABLE

portMPU_REGION_NON_SHAREABLE
portMPU_REGION_PRIVILEGED_READ_ONLY

What about normal FLASH memory area attributes ? Are they by default the same ?

MPU default settings can keep those areas with privileged access right what is OK for me.

But If I not specify others, may be some performance penalty or some other degradation can happens.

In can see in FreeRTOS port for LPC, some area is covered explicitly with those attributes as well.

Can those code area stay as it is or extra MPU atrributes bring some required settings and/or benefits ?

Regards,

Eugene

Re: LPC55S69: Boot-Rom area attributes

diego_charles — Wed, 24 Jun 2020 03:41:24 GMT

Hi Eugene,

I just wanted to let you know that I am working to provide feedback on your inquiries.

Regards,

Diego.

Re: LPC55S69: Boot-Rom area attributes

diego_charles — Tue, 30 Jun 2020 19:03:40 GMT

Hi Eugene,

Thank you for your patience,

We could consider the Boot ROM and normal FLASH as normal memory for the MPU.

However, the definition of their attributes for memory regions will depend on your application, this includes the privilege attribute.

Unfortunately ,we do not have specific examples to define a memory region in MPU for the BootROM for your reference.

If we check the prvSetupMPU() , from FreeRTOS port.c we can see that already 5 MPU regions are defined for the kernel operation:

#define portPRIVILEGED_FLASH_REGION                                                                   ( 0UL )
#define portUNPRIVILEGED_FLASH_REGION                                                              ( 1UL )
#define portUNPRIVILEGED_SYSCALLS_REGION                                                       ( 2UL )
#define portPRIVILEGED_RAM_REGION                                                                       ( 3UL )
#define portSTACK_REGION                                                                                          ( 4UL )

For example, privileged flash has the region 0 assigned. The attributes for this specific Flash area are defined using the RBAR register of the MPU.

   portMPU_RNR_REG = portPRIVILEGED_FLASH_REGION;// equals to region number 0 of the MPU
       portMPU_RBAR_REG =   ( ( ( uint32_t ) __privileged_functions_start__ ) & portMPU_RBAR_ADDRESS_MASK ) |
                               ( portMPU_REGION_NON_SHAREABLE ) |   ( portMPU_REGION_PRIVILEGED_READ_ONLY );

By default the MPU blocks access to the memory areas that are not explicitly configured on the MPU for any privileged or unprivileged program.

However, we can see that the last sentence of the prvSetupMPU() function:

portMPU_CTRL_REG |= ( portMPU_PRIV_BACKGROUND_ENABLE | portMPU_ENABLE );

Enables the MPU and the PRIVDEFENA bit . The last bit will enable the access to the un-mapped

Memory areas to privileged privileged programs. For example, this means that a privileged function can access to SRAM areas that were not defined on the MPU .

You could leave the five regions defined by FreeRTOS as they are. If we check closer only necessary attributes are granted for proper kernel operation.

I hope this helps

Regards,

Diego

Re: LPC55S69: Boot-Rom area attributes

EugeneHiihtaja — Wed, 01 Jul 2020 10:39:39 GMT

Hi Diego !

Thank you !

I think I can keep it as it is because PRIV_BACKGROUND is enabled for MPU_S and SAU is not enable access to it from Nonsecure side.

Regards,

Eugene