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Low level access to Cortex-A processors.

Currently Supported Execution States

  • [x] AArch64
  • [ ] AArch32

Minimum Supported Rust Version

Requires a recent nightly of Rust if the (default) nightly feature is enabled. Without this the register access module is not available.


Please note that for using this crate's register definitions (as provided by cortex_a::registers::*), you need to also include tock-registers in your project. This is because the interface traits provided by tock-registers are implemented by this crate. You should include the same version of tock-registers as is being used by this crate to ensure sane interoperatbility.

For example, in the following snippet, X.Y.Z should be the same version of tock-registers that is mentioned in cortex-a's Cargo.toml.

name = "Your embedded project"

# Some parts omitted for brevity.

tock-registers = "X.Y.Z"
cortex-a = "A.B.C"       # <-- Includes tock-registers itself.


Check out for usage examples. Listed below is a snippet of rust-raspberrypi-OS-tutorials's early boot code.

use cortex_a::{asm, registers::*};
use tock_registers::interfaces::Writeable; // <-- Trait needed to use `write()` and `set()`.

// Some parts omitted for brevity.

unsafe fn prepare_el2_to_el1_transition(
    virt_boot_core_stack_end_exclusive_addr: u64,
    virt_kernel_init_addr: u64,
) {
    // Enable timer counter registers for EL1.

    // No offset for reading the counters.

    // Set EL1 execution state to AArch64.

    // Set up a simulated exception return.
            + SPSR_EL2::A::Masked
            + SPSR_EL2::I::Masked
            + SPSR_EL2::F::Masked
            + SPSR_EL2::M::EL1h,


Descriptive comments in the source files are taken from the ARM Architecture Reference Manual ARMv8, for ARMv8-A architecture profile.


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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