Add signed/fixedpoint properties (#140)

* declared intwidth, fracwidth, and is_signed UDPs

* fix boolean type name in UDP definition

* generate hwif fields with fixedpoint indices

* make "counter" and "encode" properties mutualy exclusive with signed/fixedpoint

* add signed/unsigned to hwif

* improved fixedpoint error messages, added validation tests

* added fixedpoint tests

* fixedpoint/signed not allowed for signal components

* added signed/fixedpoint UDP docs

* handle single-bit fixedpoint numbers

* fix too many positional arguments lint

* changed spelling of fixedpoint to fixed-point

* use "logic" in place of "unsigned logic"

* split signed and fixedpoint docs, added examples

* allow enums with is_signed=false

* split signed and fixedpoint implementations

* assorted nits picked

* updated is_signed validation unit test

src/peakrdl_regblock/struct_generator.py

@@ -88,16 +88,30 @@ class StructGenerator:
         self._struct_stack.append(s)
 
 
-    def add_member(self, name: str, width: int = 1, array_dimensions: Optional[List[int]] = None) -> None:
+    def add_member(
+            self,
+            name: str,
+            width: int = 1,
+            array_dimensions: Optional[List[int]] = None,
+            *,
+            lsb: int = 0,
+            signed: bool = False,
+    ) -> None:
         if array_dimensions:
             suffix = "[" + "][".join((str(n) for n in array_dimensions)) + "]"
         else:
             suffix = ""
 
-        if width == 1:
-            m = f"logic {name}{suffix};"
+        if signed:
+            sign = "signed "
         else:
-            m = f"logic [{width-1}:0] {name}{suffix};"
+            # the default 'logic' type is unsigned per SV LRM 6.11.3
+            sign = ""
+
+        if width == 1 and lsb == 0:
+            m = f"logic {sign}{name}{suffix};"
+        else:
+            m = f"logic {sign}[{lsb+width-1}:{lsb}] {name}{suffix};"
         self.current_struct.children.append(m)