Examples: Clarify extern section

Some beginners are confused about the "extern" section, so I added an
explanation comment to all examples. Furthermore, using the UARTx
interrupts when UART is actually being used in the same example may be
confusing, so I changed them all to SSI0/QEI0.

1 files changed, 4 insertions, 1 deletions

diff --git a/examples/t-stask-main.rs b/examples/t-stask-main.rs
index 4245ef2..f270940 100644
--- a/examples/t-stask-main.rs
+++ b/examples/t-stask-main.rs
@@ -18,7 +18,10 @@ const APP: () = {
         debug::exit(debug::EXIT_SUCCESS);
     }
 
+    // RTIC requires that unused interrupts are declared in an extern block when
+    // using software tasks; these free interrupts will be used to dispatch the
+    // software tasks.
     extern "C" {
-        fn UART0();
+        fn SSI0();
     }
 };