MPU

Memory Protection Unit regions. More...

Data Structures
struct	MpuRegion
	MPU region, described by its real base and size. More...

Enumerations
enum	MpuCachePolicy { MpuCachePolicy_NotCacheable , MpuCachePolicy_WriteThrough , MpuCachePolicy_WriteBackWriteAllocate , MpuCachePolicy_WriteBackNoWriteAllocate }
	Cache policy of a region. More...
enum	MpuPermissions {   MpuPermissions_NoAccess , MpuPermissions_PrivRW , MpuPermissions_PrivRW_UserRO , MpuPermissions_PrivRW_UserRW ,   MpuPermissions_PrivRO , MpuPermissions_PrivRO_UserRO , MpuPermissionsCount }
	Access permissions of a region. More...

Functions
void	mpu_enable (void)
	Enable the MPU.
void	mpu_disable (void)
	Disable the MPU.
void	mpu_set_region (const MpuRegion *region)
	Program a region.
MpuRegion	mpu_get_region (int region_num)
	Read back a programmed region.
void	mpu_get_register_settings (const MpuRegion *region, uint32_t *base_address_reg, uint32_t *attributes_reg)
	Compute the register values for a region without programming it.
bool	mpu_memory_is_cachable (const void *addr)
	Check whether an address may be cached.
void	mpu_init_region_from_region (MpuRegion *copy, const MpuRegion *from, bool allow_user_access)
	Copy a privileged read/write region, optionally granting unprivileged access.

Detailed Description

Memory Protection Unit regions.

Backends exist for ARMv7-M and ARMv8-M. Regions are described by their real base and size; the backend derives the hardware encoding.

const MpuRegion region = {
  .region_num = 3,
  .enabled = true,
  .base_address = (uintptr_t)buf,
  .size = sizeof(buf),
  .cache_policy = MpuCachePolicy_WriteBackWriteAllocate,
  .permissions = MpuPermissions_PrivRW,
};
 
mpu_set_region(&region);

---

Data Structure Documentation

MpuRegion

struct MpuRegion

MPU region, described by its real base and size.

The ARMv7-M backend rounds the region up to a power-of-two block and computes the subregion mask; the ARMv8-M backend programs the limit register directly.

Data Fields
uintptr_t	base_address	Base address, 32-byte aligned.
MpuCachePolicy	cache_policy	Cache policy.
bool	enabled: 1	Region is enabled.
bool	executable: 1	Allow instruction fetch (XN=0). Defaults to non-executable. Flash, app RAM, worker RAM and any code relocated to RAM must opt in.
MpuPermissions	permissions	Access permissions.
uint8_t	region_num: 4	Region number, 0 to 15.
uint32_t	size	Size in bytes.

Enumeration Type Documentation

MpuCachePolicy

enum MpuCachePolicy

Cache policy of a region.

Enumerator
MpuCachePolicy_NotCacheable	Not cacheable.
MpuCachePolicy_WriteThrough	Write-through.
MpuCachePolicy_WriteBackWriteAllocate	Write-back, write-allocate.
MpuCachePolicy_WriteBackNoWriteAllocate	Write-back, no write-allocate.

MpuPermissions

enum MpuPermissions

Access permissions of a region.

The backends map these to the hardware AP encoding (3 bits on ARMv7-M, 2 bits on ARMv8-M). The two-bit ARMv8-M field cannot express two of them precisely:

• MpuPermissions_NoAccess degrades to MpuPermissions_PrivRO, which still allows privileged reads. Use PSPLIM, not this, for thread stack overflow detection.
• MpuPermissions_PrivRW_UserRO is aliased to MpuPermissions_PrivRW_UserRW, so unprivileged code gains write access.

Enumerator
MpuPermissions_NoAccess	No access.
MpuPermissions_PrivRW	Privileged read/write, no unprivileged access.
MpuPermissions_PrivRW_UserRO	Privileged read/write, unprivileged read-only.
MpuPermissions_PrivRW_UserRW	Privileged and unprivileged read/write.
MpuPermissions_PrivRO	Privileged read-only, no unprivileged access.
MpuPermissions_PrivRO_UserRO	Privileged and unprivileged read-only.
MpuPermissionsCount	Number of permission sets.

Function Documentation

mpu_disable()

void mpu_disable

(

void

)

Disable the MPU.

mpu_enable()

void mpu_enable

(

void

)

Enable the MPU.

The default memory map stays enabled as a background region for privileged code.

mpu_get_region()

MpuRegion mpu_get_region

(

int

region_num

)

Read back a programmed region.

Parameters

region_num

Region number.

Returns

Region as decoded from the hardware registers.

mpu_get_register_settings()

void mpu_get_register_settings	(	const MpuRegion *	region,
		uint32_t *	base_address_reg,
		uint32_t *	attributes_reg
	)

Compute the register values for a region without programming it.

Parameters

	region	Region to encode.
[out]	base_address_reg	Value for the RBAR register.
[out]	attributes_reg	Value for the RASR (ARMv7-M) or RLAR (ARMv8-M) register.

mpu_init_region_from_region()

void mpu_init_region_from_region	(	MpuRegion *	copy,
		const MpuRegion *	from,
		bool	allow_user_access
	)

Copy a privileged read/write region, optionally granting unprivileged access.

Used to switch app and worker RAM regions on task switches.

Parameters

[out]	copy	Destination region.
	from	Source region; must be MpuPermissions_PrivRW.
	allow_user_access	Grant unprivileged read/write access in copy.

mpu_memory_is_cachable()

bool mpu_memory_is_cachable

(

const void *

addr

)

Check whether an address may be cached.

Only SRAM is considered cacheable, and only while the data cache is enabled.

Parameters

addr	Address to check.

Returns

true if addr is cacheable.

mpu_set_region()

void mpu_set_region

(

const MpuRegion *

region

)

Program a region.

Parameters

region

Region to program, in slot MpuRegion::region_num.