Add EEPROM example

Author: dylanmckay

examples/eeprom.rs

@@ -0,0 +1,57 @@
+//! A persistent number counter.
+//!
+//! Chose random numbers in a loop until we have chosen 1000 odd numbers.
+//! If the device is reset it will continue, keeping track of the previous number
+//! of odd numbers.
+
+#![no_std]
+#![no_main]
+
+#![feature(lang_items, unwind_attributes)]
+
+extern crate avr_libc;
+
+use avr_libc::{eeprom_read_dword, eeprom_write_dword, random};
+
+#[no_mangle]
+pub extern fn main() {
+    let mut failed_attempts = load_failed_attempts();
+
+    while failed_attempts < 1000 {
+        // odd numbers are bad
+        if unsafe { random() } & 0b1 == 0b1 {
+            failed_attempts += 1;
+        }
+
+        save_failed_attempts(failed_attempts);
+    }
+}
+
+fn load_failed_attempts() -> u32 {
+    unsafe {
+        let addr = 12 as *mut u32; // chosen arbitrarily
+        eeprom_read_dword(addr)
+    }
+}
+
+fn save_failed_attempts(attempts: u32) {
+    unsafe {
+        let addr = 12 as *mut u32; // chosen arbitrarily
+        eeprom_write_dword(addr, attempts);
+    }
+}
+
+// These do not need to be in a module, but we group them here for clarity.
+pub mod std {
+    #[lang = "eh_personality"]
+    #[no_mangle]
+    pub unsafe extern "C" fn rust_eh_personality(_state: (), _exception_object: *mut (), _context: *mut ()) -> () {
+    }
+
+    #[lang = "panic_fmt"]
+    #[unwind]
+    pub extern fn rust_begin_panic(_msg: (), _file: &'static str, _line: u32) -> ! {
+        loop { }
+    }
+}
+