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//! # `shared` //! //! A moderately low cost, easy to use, safe abstraction for sharing //! data between application and interrupt context. //! //! ## Example //! //! ```rust //! use nrf52832_pac::Interrupt; //! use bare_metal; //! use cortex_m; //! //! // Tuples are of the format: //! // (VARIABLE_NAME, VARIABLE_TYPE, CORRESPONDING_INTERRUPT), //! shared!( //! (RADIO_PKTS, usize, Interrupt::RADIO), //! (WALL_CLOCK, usize, Interrupt::RTC0), //! ); //! //! #[entry] //! fn main() { //! // Using a `shared` data item in non-interrupt context //! // requires a token. This is a singleton, sort of like //! // the peripherals from a peripheral access crate //! let mut token = RADIO_PKTS::set_initial(27).unwrap(); //! //! // You access the data from within a closure. The interrupt //! // this data is shared with is disabled for the duration of //! // the closure. Other interrupts may still occur. //! token.modify_app_context(|y| { //! *y -= 1; //! y //! }).unwrap(); //! } //! //! #[interrupt] //! fn RADIO() { //! // Within an interrupt, access is only granted if it matches //! // the declared interrupt. Inside the `RADIO` interrupt here, //! // only `RADIO_PKTS` is accessible. //! // //! // Access from within an interrupt doesn't require a token. //! RADIO_PKTS::modify_int_context(|x| { //! *x += 1; //! x //! }).unwrap(); //! } //! //! #[interrupt] //! fn RTC0() { //! // If `set_initial` was never called, then all attempts to //! // access will return an `Err`. This code would panic at //! // runtime! //! BAZ::modify_int_context(|x| { //! *x += 1; //! x //! }).unwrap(); //! } //! ``` #![no_std] #[macro_export] macro_rules! shared { ( $(($NAME:ident, $dat_ty:ty, $int:expr),)+ ) => { /// Re-export all the structures at the top level, making them /// visible at the scope the macro was used (not necessarily global!) pub use shared_internals::structs::*; /// This module is basically just here to hide all of the stuff /// from being public #[doc(hidden)] pub mod shared_internals { /// These are the actual data structures that back the /// shared data mod singletons { $( pub static mut $NAME: Option<$dat_ty> = None; )+ } /// These flags are used to prevent re-entrant calls from within /// an interrupt mod flags { use ::core::sync::atomic::AtomicBool; $( pub static $NAME: AtomicBool = AtomicBool::new(false); )+ } /// This is the primary interface to the shared data. The struct itself /// is actually an opaque zero sized type, with methods that grab data /// from the `flags` and `singletons` modules pub mod structs { use ::core::sync::atomic::Ordering; use ::cortex_m::peripheral::NVIC; use ::bare_metal::Nr; // This is bad. I don't know how else to generically get // the interrupt enum provided by the -PAC though. // PRs welcome :) use super::super::Interrupt; $( pub struct $NAME { _private: () } impl $NAME { /// Set the initial value of the shared data. This must be done /// from application context, not interrupt context. /// /// This function must be called before the `modify_*` methods /// can be used, otherwise they will return errors. pub fn set_initial(data: $dat_ty) -> Result<$NAME, $dat_ty> { if int_is_enabled($int) || super::flags::$NAME.load(Ordering::SeqCst) { return Err(data); } if unsafe { super::singletons::$NAME.is_none() } { unsafe { super::singletons::$NAME = Some(data); } Ok($NAME { _private: () }) } else { Err(data) } } /// Access the shared data from the application (non-interrupt) context. /// The interrupt must not be active when calling this function. /// /// During the scope of the closure, the corresponding interrupt will be /// disabled to prevent concurrent access. pub fn modify_app_context<F>(&mut self, f: F) -> Result<(), ()> where for<'w> F: FnOnce(&'w mut $dat_ty) -> &'w mut $dat_ty, { // theoretical race condition: if an interrupt enables this interrupt between // the next line and the line after let enabled = int_is_enabled($int); if enabled { disable_int($int); } if int_is_active($int) || unsafe { super::singletons::$NAME.is_none() } { if enabled { enable_int($int); } return Err(()); } unsafe { f(super::singletons::$NAME.as_mut().unwrap()); } if enabled { enable_int($int); } Ok(()) } /// Access the shared data from the interrupt context. This function will /// only work if the corresponding interrupt is currently active. This /// function is not re-entrant - you cannot grab the shared data more than /// once. pub fn modify_int_context<F>(f: F) -> Result<(), ()> where for<'w> F: FnOnce(&'w mut $dat_ty) -> &'w mut $dat_ty, { if !int_is_active($int) || unsafe { super::singletons::$NAME.is_none() } || super::flags::$NAME.swap(true, Ordering::SeqCst) { return Err(()); } unsafe { f(super::singletons::$NAME.as_mut().unwrap()); } assert!(super::flags::$NAME.swap(false, Ordering::SeqCst)); Ok(()) } } )+ ///////////////////////////////////////////////////////// // This section comes from the cortex-m crate. // // Ideally, we wouldn't need to copy/paste code, but // I don't think it's possible to use these functions without // having a mutable reference to the NVIC, which would require // something taking ownership of it. // // PRs welcome if this could be done better! ///////////////////////////////////////////////////////// /// This method comes from `cortex-m::NVIC` fn int_is_enabled<I>(interrupt: I) -> bool where I: Nr, { let nr = interrupt.nr(); let mask = 1 << (nr % 32); // NOTE(unsafe) atomic read with no side effects unsafe { ((*NVIC::ptr()).iser[usize::from(nr / 32)].read() & mask) == mask } } /// This method comes from `cortex-m::NVIC` fn int_is_active<I>(interrupt: I) -> bool where I: Nr { let nr = interrupt.nr(); let mask = 1 << (nr % 32); // NOTE(unsafe) atomic read with no side effects unsafe { ((*NVIC::ptr()).iabr[usize::from(nr / 32)].read() & mask) == mask } } /// This method comes from `cortex-m::NVIC` fn disable_int<I>(interrupt: I) where I: Nr { let nr = interrupt.nr(); unsafe { (*NVIC::ptr()).icer[usize::from(nr / 32)].write(1 << (nr % 32)) } } /// This method comes from `cortex-m::NVIC` fn enable_int<I>(interrupt: I) where I: Nr { let nr = interrupt.nr(); unsafe { (*NVIC::ptr()).iser[usize::from(nr / 32)].write(1 << (nr % 32)) } } } } } }