Use test helper macros for mtopi CSR field testing

Replace manual assertions with test_ro_csr_field! macro that follows
the same pattern as test_csr_field! but adapted for read-only CSRs.

Author: KushalMeghani1644

riscv/src/register/mtopi.rs

@@ -76,30 +76,44 @@ impl Mtopi {
 mod tests {
     use super::*;
 
+    macro_rules! test_ro_csr_field {
+        // test a multi-bit bitfield for read-only CSR
+        ($reg:ident, $field:ident: [$start:expr, $end:expr]) => {{
+            let bits = $reg.bits();
+            let shift = $end - $start + 1;
+            let mask = (1usize << shift) - 1;
+            let exp_val = (bits >> $start) & mask;
+
+            // Test that field extraction matches expected value
+            assert_eq!($reg.$field(), exp_val);
+        }};
+    }
+
     #[test]
     fn test_mtopi_fields() {
-        let mtopi = Mtopi::from_bits(0);
+        let mut mtopi = Mtopi::from_bits(0);
+
+        // Test iid field [16:27] with zero bits
+        test_ro_csr_field!(mtopi, iid: [16, 27]);
+        // Test ipid field [0:7] with zero bits
+        test_ro_csr_field!(mtopi, ipid: [0, 7]);
 
-        assert_eq!(mtopi.iid(), 0);
-        assert_eq!(mtopi.ipid(), 0);
         assert!(!mtopi.has_interrupt());
         assert_eq!(mtopi.priority(), 0);
         assert_eq!(mtopi.interrupt_id(), 0);
 
         // Test with some interrupt pending (IID = 11, IPID = 5)
-        let mtopi = Mtopi::from_bits((11 << 16) | 5);
-
-        assert_eq!(mtopi.iid(), 11);
-        assert_eq!(mtopi.ipid(), 5);
+        mtopi = Mtopi::from_bits((11 << 16) | 5);
+        test_ro_csr_field!(mtopi, iid: [16, 27]);
+        test_ro_csr_field!(mtopi, ipid: [0, 7]);
         assert!(mtopi.has_interrupt());
         assert_eq!(mtopi.priority(), 5);
         assert_eq!(mtopi.interrupt_id(), 11);
 
-        // Test maximum values
-        let mtopi = Mtopi::from_bits((0xFFF << 16) | 0xFF);
-
-        assert_eq!(mtopi.iid(), 0xFFF);
-        assert_eq!(mtopi.ipid(), 0xFF);
+        // Test maximum values for each field
+        mtopi = Mtopi::from_bits((0xFFF << 16) | 0xFF);
+        test_ro_csr_field!(mtopi, iid: [16, 27]);
+        test_ro_csr_field!(mtopi, ipid: [0, 7]);
         assert!(mtopi.has_interrupt());
     }