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HowToUseMPU.md

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MPU

  • It supports 12 or 16 memory regions, depending on the configuration(ARMv7-R has 12 memory regions).
  • Each region should be programmed with a base address and size.

MPU Initialization and Memory Region Setup

Initialzation of MPU is done by setting up memory regions. Memory regions are set up by using the functions in below table and each function requires 2 arguments which are Region Base Address and Region Size to setup a memory region.

The functions with name _priv_ are used to configure the kernel(Privileged) MPU regions whereas the _user_ functions are called to configure the user(Un-Privileged) MPU regions.

MPU region setup related macros and functions are defined in mpu.h under os/arch/arm/src/armv7-r/ directory.

-----------------------------------
       MPU Memory Region Info
-----------------------------------
RNUM:	int32 - Region Number
RBASE:	int32 - Region Base Address
RSIZE:	int32 - Region Size
RATTR:	int32 - Region Attirbute
-----------------------------------

------------------------------------------------------------------
            MPU Init or Memory Region Setup Functions
------------------------------------------------------------------
mpu_control() : This function is used to Enable or Diable the MPU.
------------------------------------------------------------------
                       Memory Region Access Permission Attributes
                             Privileged      Un-Privileged
------------------------------------------------------------------
mpu_priv_stronglyordered() : Read Write        No Access
mpu_priv_noncache()        : Read Only         No Access
mpu_peripheral()           : Read Write        No Access
mpu_priv_flash()           : Read Only         No Access
mpu_user_flash()           : Read Only         Read Only
mpu_priv_intsram()         : Read Write        No Access
mpu_user_intsram()         : Read Write        Read Write
mpu_priv_extsram()         : Read Write        No Access
mpu_user_extsram()         : Read Write        Read Write
mpu_priv_intsram_wb()      : Read Write        No Access
mpu_user_intsram_wb()      : Read Write        Read Write
------------------------------------------------------------------

Memory Region Setup Functions

mpu_priv_stronglyordered() - This function is used to configure a memory region as strongly ordered memory with not cacheable, not bufferable and shareable attributes.

mpu_priv_noncache() - This function is used to configure a memory region as internal memory with not cacheable, not bufferable, shareable and instruction access disable attributes.

mpu_peripheral() - This function is used to configure a memory region as periperal address space with shareable, bufferable and instruction access disable attributes.

mpu_priv_flash() - This function is used to configure a memory region as privileged program flash with cacheable attributes.

mpu_user_flash() - This function is used to configure a memory region as user program flash with cacheable attributes.

mpu_priv_intsram() - This function is used to configure a memory region as privileged internal SRAM region with shareable, cacheable attributes.

mpu_user_intsram() - This function is used to configure a memory region as user internal SRAM with shareable, cacheable attributes.

mpu_priv_extsram() - This function is used to configure a memory region as privileged external SRAM region with shareable, cacheable and bufferable attributes.

mpu_user_extsram() - This function is used to configure a memory region as user external SRAM region with shareable, cacheable and bufferable attributes.

mpu_priv_intsram_wb() - This function is similar to mpu_priv_intsram() but with WB/WA cache policy.

mpu_user_intsram_wb() - This function is similar to mpu_user_intsram() but with WB/WA cache policy.

Example:

#ifdef CONFIG_ARMV7M_MPU
int s5j_mpu_initialize(void)
{
#ifdef CONFIG_ARCH_CHIP_S5JT200
	/*
	 * Vector Table		0x02020000	0x02020FFF	4
	 * Reserved		0x02021000	0x020217FF	2
	 * BL1			0x02021800	0x020237FF	8
	 * TizenRT		0x02023800	0x0210FFFF	946(WBWA)
	 * WIFI			0x02110000	0x0215FFFF	320(NCNB)
	 */

	/* Region 0, Set read only for memory area */
	mpu_priv_flash(0x0, 0x80000000);

	/* Region 1, for ISRAM(0x02020000++1280KB, RW-WBWA */
	mpu_user_intsram_wb(S5J_IRAM_PADDR, S5J_IRAM_SIZE);

	/* Region 2, wifi driver needs non-$(0x02110000++320KB, RW-NCNB */
	mpu_priv_noncache(S5J_IRAM_PADDR + ((4 + 2 + 8 + 946) * 1024), (320 * 1024));

	/* Region 3, for FLASH area, default to set WBWA */
	mpu_user_intsram_wb(S5J_FLASH_PADDR, S5J_FLASH_SIZE);

	/* region 4, for Sflash Mirror area to be read only */
	mpu_priv_flash(S5J_FLASH_MIRROR_PADDR, S5J_FLASH_MIRROR_SIZE);

	/* Region 5, for SFR area read/write, strongly-ordered */
	mpu_priv_stronglyordered(S5J_PERIPHERAL_PADDR, S5J_PERIPHERAL_SIZE);

	/*
	 * Region 6, for vector table,
	 * set the entire high vector region as read-only.
	 */
	mpu_priv_flash(S5J_IRAM_MIRROR_PADDR, S5J_IRAM_MIRROR_SIZE);

	mpu_control(true);
#endif
	return 0;
}
#endif