initialize the FPU

closes #2

Author: Jorge Aparicio

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Added
+
+- Initialize the FPU before main
+
 ## [v0.1.0] - 2016-10-04
 
 ### Added

examples/fpu.rs

@@ -0,0 +1,29 @@
+//! You can do fast, single precision, floating point math as well
+
+#![feature(asm)]
+#![no_main]
+#![no_std]
+
+#[macro_use]
+extern crate f3;
+
+#[export_name = "main"]
+pub extern "C" fn main() -> ! {
+    let x = black_box(2_f32);
+    let y = black_box(3_f32);
+    let z = black_box(x * y);
+
+    iprintln!("{} * {} = {}", x, y, z);
+
+    loop {}
+}
+
+// Magic to prevent optimizations like "constant folding" which is when LLVM
+// performs arithmetic at compile time. This is a copy of `test::black_box`.
+fn black_box<T>(x: T) -> T {
+    unsafe {
+        asm!("" :: "r"(&x));
+    }
+
+    x
+}

src/fpu.rs

@@ -0,0 +1,24 @@
+//! Floating Point Unit (FPU)
+
+use cortex_m;
+
+/// Initializes the FPU
+///
+/// # Safety
+///
+/// - Must be called once
+/// - Must be called in an interrupt-free environment
+pub unsafe fn init() {
+    let scb = cortex_m::peripheral::scb_mut();
+
+    // Enable the FPU co-processor
+    let cpacr = scb.cpacr.read();
+    scb.cpacr.write({
+        // Enable privileged access to the co-processor 10
+        const CP10: u32 = 0b01 << 20;
+        // Enable privileged access to the co-processor 11
+        const CP11: u32 = 0b01 << 22;
+
+        cpacr | CP10 | CP11
+    });
+}

src/itm.rs

@@ -23,6 +23,11 @@ impl Write for Port {
 }
 
 /// Initializes the ITM port
+///
+/// # Safety
+///
+/// - Must be called once
+/// - Must be called in an interrupt-free environment
 pub unsafe fn init() {
     let dbgmcu = peripheral::dbgmcu_mut();
     let dcb = cortex_m::peripheral::dcb_mut();

src/lib.rs

@@ -142,6 +142,7 @@ mod lang_items;
 pub mod delay;
 pub mod examples;
 pub mod exception;
+pub mod fpu;
 pub mod itm;
 pub mod led;
 pub mod peripheral;
@@ -152,6 +153,7 @@ pub mod peripheral;
 #[linkage = "weak"]
 pub unsafe extern "C" fn init() {
     delay::init();
+    fpu::init();
     itm::init();
     led::init();
 }