From 4d71c0ee76cee0bee651eb7b131bdad6a3c259b5 Mon Sep 17 00:00:00 2001
From: Rahix <rahix@rahix.de>
Date: Thu, 9 May 2019 10:58:29 +0200
Subject: [PATCH] Add interrupts and use cfg-if

Signed-off-by: Rahix <rahix@rahix.de>
---
 Cargo.toml         |  3 +-
 src/devices/mod.rs | 11 +++++---
 src/interrupt.rs   | 68 ++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs         | 31 ++++++++++++++-------
 4 files changed, 98 insertions(+), 15 deletions(-)
 create mode 100644 src/interrupt.rs

diff --git a/Cargo.toml b/Cargo.toml
index 4a32280..1598624 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,9 +5,10 @@ authors = ["Rahix <rahix@rahix.de>"]
 edition = "2018"
 
 [features]
-attiny85 = []
 atmega32u4 = []
+attiny85 = []
 
 [dependencies]
 bare-metal = "0.2.4"
 vcell = "0.1.0"
+cfg-if = "0.1.7"
diff --git a/src/devices/mod.rs b/src/devices/mod.rs
index b068eec..0ef1b14 100644
--- a/src/devices/mod.rs
+++ b/src/devices/mod.rs
@@ -1,4 +1,7 @@
-#[cfg(feature = "attiny85")]
-pub mod attiny85;
-#[cfg(feature = "atmega32u4")]
-pub mod atmega32u4;
+cfg_if::cfg_if! {
+    if #[cfg(feature = "atmega32u4")] {
+        pub mod atmega32u4;
+    } else if #[cfg(feature = "attiny85")] {
+        pub mod attiny85;
+    }
+}
diff --git a/src/interrupt.rs b/src/interrupt.rs
new file mode 100644
index 0000000..3e2a5ac
--- /dev/null
+++ b/src/interrupt.rs
@@ -0,0 +1,68 @@
+//! Interrupts
+//!
+//! For the most part, [interrupt::free] is what you want:
+//!
+//! ```
+//! atmega32u4::interrupt::free(|cs| {
+//!     // Interrupts are disabled here
+//! })
+//! ```
+
+pub use bare_metal::{CriticalSection, Mutex, Nr};
+
+#[inline]
+/// Disables all interrupts
+pub fn disable() {
+    unsafe {
+        asm!(
+            "cli" :::: "volatile"
+        );
+    }
+}
+
+#[inline]
+/// Enables all the interrupts
+///
+/// # Safety
+///
+/// - Do not call this function inside an `interrupt::free` critical section
+pub fn enable() {
+    unsafe {
+        asm!(
+            "sei" :::: "volatile"
+        );
+    }
+}
+
+/// Execute closure `f` in an interrupt-free context.
+///
+/// This as also known as a "critical section".
+pub fn free<F, R>(f: F) -> R
+where
+    F: FnOnce(&CriticalSection) -> R,
+{
+    let sreg: u8;
+
+    // Store current state
+    unsafe {
+        asm!(
+            "in $0,0x35"
+            : "=r"(sreg)
+            :
+            :
+            : "volatile"
+        );
+    }
+
+    // Disable interrupts
+    disable();
+
+    let r = f(unsafe { &CriticalSection::new() });
+
+    // Restore interrupt state
+    if sreg & 0x80 != 0x00 {
+        enable();
+    }
+
+    r
+}
diff --git a/src/lib.rs b/src/lib.rs
index d437777..e9f6a60 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,21 +1,32 @@
 #![no_std]
+#![feature(asm)]
 
-#[allow(non_camel_case_types)]
+#[allow(non_camel_case_types, unused_attributes)]
 mod devices;
 
-#[cfg(feature = "attiny85")]
-pub use crate::devices::attiny85::*;
-#[cfg(feature = "atmega32u4")]
-pub use crate::devices::atmega32u4::*;
+pub mod interrupt;
 
+cfg_if::cfg_if! {
+    if #[cfg(feature = "atmega32u4")] {
+        pub use crate::devices::atmega32u4::*;
+    } else if #[cfg(feature = "attiny85")] {
+        pub use crate::devices::attiny85::*;
+    } else {
+        compile_error!("You need to select exactly one chip as a feature!");
+    }
+}
+
+#[cfg(any(feature = "attiny85", feature = "atmega32u4"))]
 impl Peripherals {
     /// Returns all the peripherals *once*
     #[inline]
     pub fn take() -> Option<Self> {
-        if unsafe { DEVICE_PERIPHERALS } {
-            None
-        } else {
-            Some(unsafe { Peripherals::steal() })
-        }
+        interrupt::free(|_| {
+            if unsafe { DEVICE_PERIPHERALS } {
+                None
+            } else {
+                Some(unsafe { Peripherals::steal() })
+            }
+        })
     }
 }
-- 
2.49.0