diff --git a/extra/assembly/amd/dsl2.py b/extra/assembly/amd/dsl2.py
index 78891706b6..679ab84b9e 100644
--- a/extra/assembly/amd/dsl2.py
+++ b/extra/assembly/amd/dsl2.py
@@ -62,11 +62,8 @@ v = src[256:511]         # VGPR0-255
 # ══════════════════════════════════════════════════════════════
 
 class BitField:
-  required_size = None
   def __init__(self, hi: int, lo: int):
     self.hi, self.lo = hi, lo
-    if self.required_size is not None and (hi - lo + 1) != self.required_size:
-      raise RuntimeError(f"wrong size field: expected {self.required_size}, got {hi - lo + 1}")
   def mask(self) -> int: return (1 << (self.hi - self.lo + 1)) - 1
   def encode(self, val) -> int: return val
   def decode(self, val): return val
@@ -95,26 +92,34 @@ class EnumBitField(BitField):
 # Typed fields
 # ══════════════════════════════════════════════════════════════
 
-class VGPRField(BitField):
-  required_size = 8
-  def encode(self, val):
-    if not isinstance(val, Reg) or val.offset < 256 or val.offset >= 512:
-      raise RuntimeError(f"VGPRField requires VGPR, got {val}")
-    return val.offset - 256
-  def decode(self, raw): return src[256 + raw]
-
 class SrcField(BitField):
-  required_size = 9
+  _valid_range = (0, 511)  # inclusive
   _FLOAT_ENC = {0.5: 240, -0.5: 241, 1.0: 242, -1.0: 243, 2.0: 244, -2.0: 245, 4.0: 246, -4.0: 247}
+
+  def __init__(self, hi: int, lo: int):
+    super().__init__(hi, lo)
+    expected_size = self._valid_range[1] - self._valid_range[0] + 1
+    actual_size = 1 << (hi - lo + 1)
+    if actual_size != expected_size:
+      raise RuntimeError(f"{self.__class__.__name__}: field size {hi - lo + 1} bits ({actual_size}) doesn't match range {self._valid_range} ({expected_size})")
+
   def encode(self, val):
-    if isinstance(val, Reg): return val.offset
-    if isinstance(val, float):
-      if val not in self._FLOAT_ENC: raise RuntimeError(f"SrcField: unsupported float constant {val}")
-      return self._FLOAT_ENC[val]
-    if isinstance(val, int) and 0 <= val <= 64: return 128 + val
-    if isinstance(val, int) and -16 <= val < 0: return 192 - val
-    raise RuntimeError(f"SrcField: invalid value {val}")
-  def decode(self, raw): return src[raw]
+    if isinstance(val, Reg): offset = val.offset
+    elif isinstance(val, float):
+      if val not in self._FLOAT_ENC: raise RuntimeError(f"unsupported float constant {val}")
+      offset = self._FLOAT_ENC[val]
+    elif isinstance(val, int) and 0 <= val <= 64: offset = 128 + val
+    elif isinstance(val, int) and -16 <= val < 0: offset = 192 - val
+    else: raise RuntimeError(f"invalid value {val}")
+    if not (self._valid_range[0] <= offset <= self._valid_range[1]):
+      raise RuntimeError(f"{self.__class__.__name__}: {val} (offset {offset}) out of range {self._valid_range}")
+    return offset - self._valid_range[0]
+
+  def decode(self, raw): return src[raw + self._valid_range[0]]
+
+class VGPRField(SrcField): _valid_range = (256, 511)
+class SGPRField(SrcField): _valid_range = (0, 127)
+class SSrcField(SrcField): _valid_range = (0, 255)
 
 # ══════════════════════════════════════════════════════════════
 # Inst base class