First public commit.

lenser/atari/car.py

@@ -0,0 +1,20 @@
+"""Write an Atari .car cartridge image (CART header + ROM)."""
+
+from __future__ import annotations
+
+import struct
+
+TYPE_STD_16K = 2                 # "Standard 16 KB cartridge"
+
+
+def write_car(rom: bytes, path: str, cart_type: int = TYPE_STD_16K) -> str:
+    """Wrap a cart `rom` in the .car container (16-byte CART header + ROM).
+    The header holds the cartridge type and a checksum (sum of all ROM bytes)."""
+    header = bytearray(16)
+    header[0:4] = b"CART"
+    struct.pack_into(">I", header, 4, cart_type)
+    struct.pack_into(">I", header, 8, sum(rom) & 0xFFFFFFFF)
+    with open(path, "wb") as f:
+        f.write(header)
+        f.write(rom)
+    return path