Low level access to MSP430 microcontrollers
This crate is based on cortex-m crate by Jorge Aparicio (@japaric).
This crate requires a nightly rust due to the use of the new asm! (0.3.0 and above), llvm_asm! (0.2.2) or old asm! (0.2.1 and below) macros. The below table contains compilers which are known to work:
msp430 version rustc compiler 0.3.0 nightly-2022-01-24 0.2.2 nightly-2020-04-22 0.2.1 nightly-2020-01-04
The critical-section-single-core feature provides a critical section implementation based upon disabling interrupts.
Critical sections by disabling interrupts are a valuable way to access I/O and shared data safely in msp430. However, rustc/LLVM does not always optimize critical sections well in terms of space. For example, sometimes rustc/LLVM will create two copies of interrupt enable assembly code when exiting a critical section that contains a branch- one copy each for branch-taken/branch-not-taken.
This crate provides three features for giving hints to rustc/LLVM for how to optimize critical sections for size. Both critical_section::with and the interrupt::free critical sections are supported, with and without the critical-section feature above:
outline-cs-acq: Hint to rustc/LLVM that each critical section entry should be a call to a single copy of an acquire function (disable interrupts).outline-cs-rel: Hint to rustc/LLVM that each critical section exit should be a call to a single copy of a release function (enable interrupts if not in a nested critical section).outline-cs: Convenience feature for enabling both of the above at the same time.If saving space is a concern in your application, you should experiment with which features provide the best size savings and balance this against the execution overhead of the extra function calls due to outlining. The execution overhead of enabling each hint is ~5 + 2 clock cycles for each critical section- at least a CALL and RET instruction.
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