Trait bern_arch::memory_protection::IMemoryProtection

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pub trait IMemoryProtection {
    type MemoryRegion;

    fn enable_memory_protection();
    fn disable_memory_protection();
    fn enable_memory_region(region: u8, config: Config);
    fn disable_memory_region(region: u8);
    fn prepare_memory_region(region: u8, config: Config) -> Self::MemoryRegion;
    fn prepare_unused_region(region: u8) -> Self::MemoryRegion;
    fn apply_regions(memory_regions: &[Self::MemoryRegion; 3]);
    fn min_region_size() -> Byte;
    fn n_memory_regions() -> u8;
}

Expand description

Memory Protection.

Implementation

In addition to the trait the following features have to be implemented:

Memory Protection Exception

A violation of a memory rule will trigger an exception. The exception must call memory_protection_exception() to notify the kernel, i.e.:

extern "Rust" {
    pub fn memory_protection_exception();
}

#[allow(non_snake_case)]
#[exception]
fn MemoryManagement() -> () {
    unsafe {
        memory_protection_exception();
    }
}

Size and Alignment

Different memory protection implementation have different requirements in terms of sizes and alignment. A hardware implementation must provide

Alignment structs for all available alignments with naming convention A<size number><unit prefix (_,K,M,G)>, i.e.

ⓘ
```
#[repr(align(4_096))]
pub struct A4K;
```

A macro alignment_from_size!() that returns valid alignment for given memory size, i.e.

#[macro_export]
macro_rules! alignment_from_size {
    (4_096) => { $crate::arch::memory_protection::A4K };
    ($x:expr) => {
        compile_error!("Size does not meet alignment requirements from the MPU. \
        Compatible sizes are: 4KB");
     };
}

A macro size_from_raw!() that returns a valid size type from raw number, i.e.

#[macro_export]
macro_rules! size_from_raw {
    (4_096) => { $crate::arch::memory_protection::Size::S4K };
    ($x:expr) => {
        compile_error!("Size cannot be protected by MPU. \
        Compatible sizes are: 4KB");
     };
}

Required Associated Types

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type MemoryRegion

Precalculated memory region configuration.

Required Methods

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fn enable_memory_protection()

Enable memory protection hardware.

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fn disable_memory_protection()

Disable memory protection hardware.

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fn enable_memory_region(region: u8, config: Config)

Setup and enable one memory region.

Example

Protect all flash memory from write access, instruction fetch allowed.

Arch::enable_memory_region(
   0,
   Config {
        addr: 0x0800_0000 as *const _,
        memory: Type::Flash,
        size: Size::S512K,
        access: Access { user: Permission::ReadOnly, system: Permission::ReadOnly },
        executable: true
});