impl From<usize> for Mcause

This is useful unit tests that want test trap handlers.

riscv/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Added
+
+- Add `Mcause::from(usize)` for use in unit tests
+
 ### Fixed
 
 - Fixed `sip::set_ssoft` and `sip::clear_ssoft` using wrong address

riscv/src/register/mcause.rs

@@ -6,6 +6,13 @@ pub struct Mcause {
     bits: usize,
 }
 
+impl From<usize> for Mcause {
+    #[inline]
+    fn from(bits: usize) -> Self {
+        Self { bits }
+    }
+}
+
 /// Trap Cause
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum Trap {