Allow FixedValueEntry to be specified as hex

src/yamcs/pymdb/ccsds.py

@@ -165,30 +165,30 @@ def add_ccsds_header(system: System) -> CcsdsHeader:
         entries=[
             FixedValueEntry(
                 name="ccsds_version",
-                binary=bytes.fromhex("00"),
+                binary="00",
                 bits=3,
             ),
             FixedValueEntry(
                 name="ccsds_type",
-                binary=bytes.fromhex("01"),
+                binary="01",
                 bits=1,
             ),
             ArgumentEntry(tc_secondary_header),
             ArgumentEntry(tc_apid),
             FixedValueEntry(
                 name="ccsds_group_flags",
-                binary=bytes.fromhex("03"),  # Always standalone
+                binary="03",  # Always standalone
                 bits=2,
             ),
             FixedValueEntry(
                 name="ccsds_source_sequence_count",
-                binary=bytes.fromhex("0000"),
+                binary="0000",
                 bits=14,
                 short_description="Value set by Yamcs during link post-processing",
             ),
             FixedValueEntry(
                 name="ccsds_packet_length",
-                binary=bytes.fromhex("0000"),
+                binary="0000",
                 bits=16,
                 short_description="Value set by Yamcs during link post-processing",
             ),

src/yamcs/pymdb/commands.py

@@ -412,7 +412,7 @@ def __init__(
 class FixedValueEntry:
     def __init__(
         self,
-        binary: bytes,
+        binary: bytes | str,
         name: str | None = None,
         *,
         short_description: str | None = None,
@@ -421,17 +421,42 @@ def __init__(
         condition: Expression | None = None,
         bits: int | None = None,
     ) -> None:
-        self.binary: bytes = binary
+
+        self.binary: bytes
+        """
+        The fixed value to be encoded.
+
+        The value may be provided in any of these ways:
+
+        * Bytes: :python:`b\xDE\xAD\xBE\xEF`
+        * Hex string: :python:`"DEADBEEF"`
+        """
+        if isinstance(binary, str):
+            self.binary = bytes.fromhex(binary)
+        else:
+            self.binary = binary
 
         self.name: str | None = name
+        """Optional name"""
 
         self.short_description: str | None = short_description
-        """Onleine description"""
+        """Oneline description"""
 
         self.absolute: bool = absolute
         self.location_in_bits: int = location_in_bits
         self.condition: Expression | None = condition
+
         self.bits: int | None = bits
+        """
+        If unspecified, its value is derived from the provided
+        :attr:`binary` value.
+
+        If less than the bit size of the :attr:`binary` attribute,
+        the value is left-padded with zeros.
+
+        If larger than the bit size of the :attr:`binary` attribute,
+        the most-significant bits are dropped.
+        """
 
 
 CommandEntry = ArgumentEntry | ParameterEntry | FixedValueEntry

src/yamcs/pymdb/csp.py

@@ -260,11 +260,11 @@ def add_csp_header(
             ArgumentEntry(tc_dport),
             FixedValueEntry(
                 name=f"{prefix}sport",
-                binary=b"\x20",  # 48
+                binary="20",  # 48
                 bits=6,
                 short_description="Ephemeral port for outgoing connection",
             ),
-            FixedValueEntry(name=f"{prefix}reserved", binary=b"\x00", bits=4),
+            FixedValueEntry(name=f"{prefix}reserved", binary="00", bits=4),
             ArgumentEntry(tc_hmac),
             ArgumentEntry(tc_xtea),
             ArgumentEntry(tc_rdp),

src/yamcs/pymdb/xtce.py

@@ -437,12 +437,25 @@ def add_fixed_value_entry(
         entry: FixedValueEntry,
     ):
         el = ET.SubElement(parent, "FixedValueEntry")
-        el.attrib["binaryValue"] = hexlify(entry.binary).decode("ascii")
 
+        bitlen: int
         if entry.bits is None:
-            el.attrib["sizeInBits"] = str(8 * len(entry.binary))
+            bitlen = 8 * len(entry.binary)
         else:
-            el.attrib["sizeInBits"] = str(entry.bits)
+            bitlen = entry.bits
+
+        hex = hexlify(entry.binary).decode("ascii")
+
+        # XTCE requires hex to be at least as large as the bit size
+        bytelen: int
+        if bitlen % 8:
+            bytelen = (bitlen + (8 - bitlen % 8)) // 8
+        else:
+            bytelen = bitlen // 8
+        hex = hex.zfill(bytelen * 2)
+
+        el.attrib["binaryValue"] = hex
+        el.attrib["sizeInBits"] = str(bitlen)
 
         if entry.name:
             el.attrib["name"] = entry.name