riscv: define mvendorid CSR with macro helpers

riscv/CHANGELOG.md

@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Use CSR helper macros to define `mstatus` register
 - Use CSR helper macros to define `mstatush` register
 - Use CSR helper macros to define `mtvec` register
+- Use CSR helper macros to define `mtvendorid` register
 
 ## [v0.12.1] - 2024-10-20
 

riscv/src/register/mvendorid.rs

@@ -1,34 +1,100 @@
 //! mvendorid register
 
-use core::num::NonZeroUsize;
+read_only_csr! {
+    /// `mvendorid` register
+    Mvendorid: 0xF11,
+    mask: 0xffff_ffff,
+    sentinel: 0,
+}
+
+read_only_csr_field! {
+    Mvendorid,
+    /// Represents the number of continuation bytes (`0x7f`) in the JEDEC manufacturer ID.
+    bank: [7:31],
+}
 
-/// mvendorid register
-#[derive(Clone, Copy, Debug)]
-pub struct Mvendorid {
-    bits: NonZeroUsize,
+read_only_csr_field! {
+    Mvendorid,
+    /// Represents the final offset field in the JEDEC manufacturer ID.
+    ///
+    /// # Note
+    ///
+    /// The encoded value returned by `offset` does not include the odd parity bit (`0x80`).
+    offset: [0:6],
 }
 
 impl Mvendorid {
-    /// Returns the contents of the register as raw bits
-    #[inline]
-    pub fn bits(&self) -> usize {
-        self.bits.get()
-    }
+    /// Represents the JEDEC manufacture continuation byte.
+    pub const CONTINUATION: u8 = 0x7f;
 
-    /// Returns the JEDEC manufacturer ID
-    #[inline]
-    pub fn jedec_manufacturer(&self) -> usize {
-        self.bits() >> 7
+    /// Gets the decoded JEDEC manufacturer ID from the `mvendorid` value.
+    ///
+    /// # Note
+    ///
+    /// This function returns an iterator over the decoded bytes.
+    ///
+    /// An iterator is needed because the encoding can theoretically return a max count (`0x1ff_ffff`) of continuation bytes (`0x7f`).
+    ///
+    /// The final byte in the iterator is the `offset`, including the odd parity bit (set only if even).
+    pub fn jedec_manufacturer(&self) -> impl Iterator<Item = u8> {
+        const DONE: usize = usize::MAX;
+
+        let mut bank = self.bank();
+        let offset = self.offset();
+
+        core::iter::from_fn(move || match bank {
+            DONE => None,
+            0 => {
+                bank = DONE;
+                let parity = ((1 - (offset.count_ones() % 2)) << 7) as usize;
+                Some((parity | offset) as u8)
+            }
+            _ => {
+                bank -= 1;
+                Some(Self::CONTINUATION)
+            }
+        })
     }
 }
 
-read_csr!(0xF11);
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_mvendorid() {
+        (0..u32::BITS)
+            .map(|r| ((1u64 << r) - 1) as usize)
+            .for_each(|raw| {
+                let exp_bank = raw >> 7;
+                let exp_offset = raw & (Mvendorid::CONTINUATION as usize);
+                let exp_parity = ((1 - (exp_offset.count_ones() % 2)) << 7) as u8;
+                let exp_mvendorid = Mvendorid::from_bits(raw);
 
-/// Reads the CSR
-#[inline]
-pub fn read() -> Option<Mvendorid> {
-    let r = unsafe { _read() };
-    // When mvendorid is hardwired to zero it means that the mvendorid
-    // csr isn't implemented.
-    NonZeroUsize::new(r).map(|bits| Mvendorid { bits })
+                assert_eq!(exp_mvendorid.bank(), exp_bank);
+                assert_eq!(exp_mvendorid.offset(), exp_offset);
+
+                let mut jedec_iter = exp_mvendorid.jedec_manufacturer();
+                (0..exp_bank)
+                    .for_each(|_| assert_eq!(jedec_iter.next(), Some(Mvendorid::CONTINUATION)));
+                assert_eq!(jedec_iter.next(), Some(exp_parity | (exp_offset as u8)));
+                assert_eq!(jedec_iter.next(), None);
+            });
+
+        // ISA example used as a concrete test vector.
+
+        let exp_bank = 0xc;
+        let exp_offset = 0x0a;
+        let exp_decoded_offset = 0x8a;
+        let raw_mvendorid = 0x60a;
+        let exp_mvendorid = Mvendorid::from_bits(raw_mvendorid);
+
+        assert_eq!(exp_mvendorid.bank(), exp_bank);
+        assert_eq!(exp_mvendorid.offset(), exp_offset);
+
+        let mut jedec_iter = exp_mvendorid.jedec_manufacturer();
+        (0..exp_bank).for_each(|_| assert_eq!(jedec_iter.next(), Some(Mvendorid::CONTINUATION)));
+        assert_eq!(jedec_iter.next(), Some(exp_decoded_offset));
+        assert_eq!(jedec_iter.next(), None);
+    }
 }