Submission for the coding challenge for IDL Writer/Verification RISC-V mentorship

submissions/tsha-256/BUILD.md

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+This is a Python program. It does not use any packages besides `sys`, which is installed in the base python. To run the code, pass it as an argument to a python interpreter of your choice. While this should work for any version of Python, I can't guarantee that it will work for any version besides Python 3.12.8.
+
+Thanks for reading! I'm very excited to be a part of the RISC-V mentorship!

submissions/tsha-256/pmpcheck.py

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+import sys
+
+def load_pmp_config(file_path):
+    """Loads PMP configuration from the given file."""
+    with open(file_path, 'r') as f:
+        lines = [line.strip() for line in f.readlines()]
+        pmpcfg = [int(lines[i], 16) for i in range(64)]  # First 64 lines are pmpNcfg
+        pmpaddr = [int(lines[i], 16) for i in range(64, 128)]  # Last 64 lines are pmpaddrN
+
+        return pmpcfg, pmpaddr
+
+def check_pmp_access(pmpcfg, pmpaddr, addr, mode):
+    """Checks whether the given address would cause an access fault."""
+    addr_match = False
+    for i in range(64):
+        cfg = pmpcfg[i]
+        addr_0 = pmpaddr[i] << 2  # Convert PMP address format
+        L = (cfg >> 7) & 0b1  # Lock bit
+        O = (cfg >> 5) & 0b11 # Unused bits
+        A = (cfg >> 3) & 0b11 # Address-matching mode
+        X = (cfg >> 2) & 0b1  # Execute permission
+        W = (cfg >> 1) & 0b1  # Write permission
+        R = (cfg >> 0) & 0b1  # Read permission
+
+        rwx = (0, 0, 0)  # Default deny
+
+        if A == 0b00: # Null (Disabled)
+            continue
+        elif A == 0b01:  # TOR
+            if i == 0:
+                prev_addr = 0
+            else:
+                prev_addr = pmpaddr[i - 1] << 2
+
+            if prev_addr <= addr < addr_0:
+                addr_match = True
+        elif A == 0b10:  # NA4
+            if addr_0 <= addr < addr_0 + 4:
+                addr_match = True
+        elif A == 0b11:  # NAPOT
+            trail = 0
+            while pmpaddr[i] & (1 << trail) != 0:
+                trail += 1  
+            size = 1 << (trail + 3)
+            if addr_0 <= addr < addr_0 + size:
+                addr_match = True
+
+        if addr_match:
+            rwx = (R, W, X)
+            break
+
+    # for ends here
+    if addr_match == False: # No PMP entry matched
+        if mode == 'M': # Machine mode default allow
+            return (1, 1, 1)
+        else: # User/Supervisor mode default deny
+            return (0, 0, 0)
+    if mode == 'M': # If address matched and in machine mode and lock bit is not set, allow
+        if L == 0:
+            return (1, 1, 1)
+    return rwx # if L is set or not in machine mode, return the permissions
+
+def main():
+    if len(sys.argv) != 5:
+        print("Usage: pmp_check <pmp_config_file> <physical_address> <mode> <operation>")
+        sys.exit(1)
+
+    fp = sys.argv[1]
+    addr = int(sys.argv[2], 16)
+    mode = sys.argv[3]
+    op = sys.argv[4]
+
+    if mode not in {'M', 'S', 'U'}:
+        print("Invalid mode. Mode must be M/S/U.")
+        sys.exit(1)    
+    if op not in {'R', 'W', 'X'}:
+        print("Invalid operation. Operation must be R/W/X.")
+        sys.exit(1)
+
+    pmpcfg, pmpaddr = load_pmp_config(fp)
+    R, W, X = check_pmp_access(pmpcfg, pmpaddr, addr, mode)
+
+    if (op == 'R' and R) or (op == 'W' and W) or (op == 'X' and X):
+        print("Access allowed.")
+    else:
+        print("Access fault.")
+
+if __name__ == "__main__":
+    main()