checkpoint: VT1200 reverse-engineering workspace before board-model work

test_reconstruct.py

@@ -0,0 +1,65 @@
+"""Tests for reconstruct.py — the VT1200 EPROM de-interleaver.
+
+The firmware's addresses are now known (see MEMORY_MAP.md): the ROM is
+top-aligned at physical byte 0x07E40000 and the EPROM *bank* order is the
+reverse of part-number order.  `reconstruct(..., linear=True)` must therefore
+emit an image where file offset == physical byte - 0x07E40000.
+"""
+import os
+import struct
+import unittest
+
+import reconstruct
+
+ROM_SIZE = 0x1C0000
+ROM_BASE = 0x07E40000
+RESET_VECTOR = 0x3F200040                 # bit address the reset entry holds
+POST_BYTES = bytes.fromhex("6003500540070056")
+# In part-number order bank0 (210/211) is first, so its reset vector -- the last
+# entry of the vector page -- lands at file offset 0x3FFFC.
+RESET_VECTOR_OFFSET_PART_ORDER = 0x3FFFC
+
+
+def _load(dirname, linear):
+    return reconstruct.reconstruct(dirname, linear=linear)[1]
+
+
+class LinearImageTest(unittest.TestCase):
+    """linear=True yields an image whose offsets are CPU-address ordered."""
+
+    def test_size(self):
+        self.assertEqual(len(_load("v2.1", linear=True)), ROM_SIZE)
+
+    def test_reset_vector_is_at_top_of_rom(self):
+        img = _load("v2.1", linear=True)
+        self.assertEqual(struct.unpack_from("<I", img, len(img) - 4)[0], RESET_VECTOR)
+
+    def test_reset_target_holds_post_code(self):
+        # 0x3F200040 >> 3 == 0x07E40008 == ROM_BASE + 8
+        img = _load("v2.1", linear=True)
+        self.assertEqual(img[8:8 + len(POST_BYTES)], POST_BYTES)
+
+    def test_vector_page_is_at_top(self):
+        linear = _load("v2.1", linear=True)
+        part = _load("v2.1", linear=False)
+        self.assertEqual(linear[-0x80:], part[0x3FF80:0x40000])
+
+    def test_known_string_pointer_resolves(self):
+        # Stored pointer 0x3F816ED8 >> 3 == ROM_BASE + 0xC2DDB
+        img = _load("v2.1", linear=True)
+        self.assertEqual(img[0xC2DDB:0xC2DDB + 15], b"Messages re-xmt")
+
+
+class PartOrderImageTest(unittest.TestCase):
+    """linear=False preserves the legacy part-number-ordered layout."""
+
+    def test_reset_vector_location(self):
+        img = _load("v2.1", linear=False)
+        self.assertEqual(
+            struct.unpack_from("<I", img, RESET_VECTOR_OFFSET_PART_ORDER)[0],
+            RESET_VECTOR,
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()