Improve CP0-disabled error message (#2061)

* Improve CP0-disabled error message

* CHANGELOG.md

esp-backtrace/CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 ### Changed
+- Print a more helpful message in case of a `Cp0Disabled` exception (#2061)
 
 ### Fixed
 

esp-backtrace/src/lib.rs

@@ -100,7 +100,7 @@ unsafe fn __user_exception(cause: arch::ExceptionCause, context: arch::Context)
 
     // Unfortunately, a different formatter string is used
     #[cfg(not(feature = "defmt"))]
-    esp_println::println!("\n\nException occurred '{:?}'", cause);
+    esp_println::println!("\n\nException occurred '{}'", cause);
 
     #[cfg(feature = "defmt")]
     defmt::error!("\n\nException occurred '{}'", cause);

esp-backtrace/src/xtensa.rs

@@ -1,4 +1,4 @@
-use core::arch::asm;
+use core::{arch::asm, fmt::Display};
 
 use crate::MAX_BACKTRACE_ADDRESSES;
 
@@ -11,7 +11,7 @@ pub(super) const RA_OFFSET: usize = 3;
 
 /// Exception Cause
 #[doc(hidden)]
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
 #[repr(C)]
 pub enum ExceptionCause {
@@ -99,6 +99,16 @@ pub enum ExceptionCause {
     None                           = 255,
 }
 
+impl Display for ExceptionCause {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        if *self == Self::Cp0Disabled {
+            write!(f, "Cp0Disabled (Access to the floating point coprocessor is not allowed. You may want to enable the `float-save-restore` feature of the `xtensa-lx-rt` crate.)")
+        } else {
+            write!(f, "{:?}", self)
+        }
+    }
+}
+
 #[doc(hidden)]
 #[allow(non_snake_case)]
 #[derive(Clone, Copy)]