First public commit.

lenser/c16/viewer/assemble.py

@@ -0,0 +1,62 @@
+"""Assemble the C16 TED viewer with `xa` and build the loadable PRG.
+
+The PRG loads at the C16 BASIC start ($1001): a BASIC stub (`10 SYS4128`)
+followed by the 7501 viewer (at $1020), the two colour matrices ($1800 / $1C00)
+and the bitmap ($2000).  MAME's quickload runs it, the stub SYSes the viewer.
+"""
+from __future__ import annotations
+
+import os
+import shutil
+import subprocess
+import tempfile
+
+VIEWER_DIR = os.path.dirname(os.path.abspath(__file__))
+
+BASIC_START = 0x1001
+ML_ORG = 0x1020
+ATTR_ORG = 0x1800          # luminance matrix (video matrix base)
+CH_ORG = 0x1C00            # hue matrix (video base | $400)
+BITMAP_ORG = 0x2000
+
+# BASIC: 10 SYS4128  ($1020 = 4128) -- bytes as they sit from $1001
+_STUB = bytes([0x0B, 0x10, 0x0A, 0x00, 0x9E,
+               0x34, 0x31, 0x32, 0x38, 0x00, 0x00, 0x00])
+
+
+class AssemblerError(RuntimeError):
+    pass
+
+
+def have_xa() -> bool:
+    return shutil.which("xa") is not None
+
+
+def _assemble() -> bytes:
+    if not have_xa():
+        raise AssemblerError("The 'xa' (xa65) assembler was not found on PATH.\n"
+                             "Install it with:  sudo apt install xa65")
+    proc = subprocess.run(["xa", "-o", "/dev/stdout", "viewer.s"],
+                          capture_output=True, cwd=VIEWER_DIR)
+    if proc.returncode != 0:
+        raise AssemblerError(f"xa failed:\n{proc.stderr.decode()}")
+    return proc.stdout
+
+
+def build_prg(payload: bytes) -> bytes:
+    """payload = bitmap(8000) + attr(1000) + ch(1000); returns the loadable PRG."""
+    bitmap, attr, ch = payload[:8000], payload[8000:9000], payload[9000:10000]
+    code = _assemble()
+    mem = bytearray()
+    mem += _STUB                                       # $1001..
+    mem += b"\x00" * (ML_ORG - BASIC_START - len(mem))
+    mem += code                                        # $1020..
+    if len(mem) > ATTR_ORG - BASIC_START:
+        raise AssemblerError("viewer code overruns the $1800 matrix area")
+    mem += b"\x00" * (ATTR_ORG - BASIC_START - len(mem))
+    mem += attr                                        # $1800..
+    mem += b"\x00" * (CH_ORG - BASIC_START - len(mem))
+    mem += ch                                          # $1C00..
+    mem += b"\x00" * (BITMAP_ORG - BASIC_START - len(mem))
+    mem += bitmap                                      # $2000..
+    return bytes([BASIC_START & 0xFF, BASIC_START >> 8]) + bytes(mem)