document how to use the heap and a dynamic allocator

src/examples/_3_crash.rs

@@ -27,7 +27,7 @@
 //! $2 = cortex_m::exception::Exception::HardFault
 //!
 //! (gdb) # Where did we come from?
-//! (gdb) print _e
+//! (gdb) backtrace
 //! ```
 //!
 //! ```

src/examples/_6_allocator.rs

@@ -0,0 +1,75 @@
+//! How to use the heap and a dynamic memory allocator
+//!
+//! To compile this example you'll need to build the collections crate as part
+//! of the Xargo sysroot. To do that change the Xargo.toml file to look like
+//! this:
+//!
+//! ``` text
+//! [dependencies.core]
+//! [dependencies.collections] # new
+//!
+//! [dependencies.compiler_builtins]
+//! features = ["mem"]
+//! git = "https://github.com/rust-lang-nursery/compiler-builtins"
+//! stage = 1
+//! ```
+//!
+//! This example depends on the alloc-cortex-m crate so you'll have to add it
+//! to your Cargo.toml:
+//!
+//! ``` text
+//! # or edit the Cargo.toml file manually
+//! $ cargo add alloc-cortex-m
+//! ```
+//!
+//! ```
+//! 
+//! #![feature(collections)]
+//! #![feature(used)]
+//! #![no_std]
+//! 
+//! // This is the allocator crate; you can use a different one
+//! extern crate alloc_cortex_m;
+//! #[macro_use]
+//! extern crate collections;
+//! #[macro_use]
+//! extern crate cortex_m;
+//! extern crate cortex_m_rt;
+//! 
+//! use cortex_m::asm;
+//! 
+//! fn main() {
+//!     // Initialize the allocator
+//!     unsafe {
+//!         extern "C" {
+//!             // Start of the heap
+//!             static mut _sheap: usize;
+//!         }
+//! 
+//!         // Size of the heap in words (1 word = 4 bytes)
+//!         // WARNING: The bigger the heap the greater the chance to run into a
+//!         // stack overflow (collision between the stack and the heap)
+//!         const SIZE: isize = 256;
+//! 
+//!         // End of the heap
+//!         let _eheap = (&mut _sheap as *mut _).offset(SIZE);
+//! 
+//!         alloc_cortex_m::init(&mut _sheap as *mut _, _eheap);
+//!     }
+//! 
+//!     // Growable array allocated on the heap
+//!     let xs = vec![0, 1, 2];
+//!     hprintln!("{:?}", xs);
+//! }
+//! 
+//! // As we are not using interrupts, we just register a dummy catch all handler
+//! #[allow(dead_code)]
+//! #[used]
+//! #[link_section = ".rodata.interrupts"]
+//! static INTERRUPTS: [extern "C" fn(); 240] = [default_handler; 240];
+//! 
+//! extern "C" fn default_handler() {
+//!     asm::bkpt();
+//! }
+//! ```
+// Auto-generated. Do not modify.

src/examples/mod.rs

@@ -6,3 +6,4 @@ pub mod _2_panic;
 pub mod _3_crash;
 pub mod _4_register_interrupt_handler;
 pub mod _5_override_exception_handler;
+pub mod _6_allocator;