Add a user-defined HardFault handler to print ExceptionFrame in crash example

examples/crash.rs

@@ -82,8 +82,10 @@
 use panic_halt as _;
 
 use core::ptr;
+use core::fmt::Write;
 
-use cortex_m_rt::entry;
+use cortex_m_rt::{entry, exception, ExceptionFrame};
+use cortex_m_semihosting::hio;
 
 #[entry]
 fn main() -> ! {
@@ -94,3 +96,12 @@ fn main() -> ! {
 
     loop {}
 }
+
+#[exception]
+fn HardFault(ef: &ExceptionFrame) -> ! {
+    if let Ok(mut hstdout) = hio::hstdout() {
+        writeln!(hstdout, "{:#?}", ef).ok();
+    }
+
+    loop {}
+}