support reading segmented UF2 files

now that we create segmented UF2 files properly in concatenate, we need
the ability to read them, which we'd previously saved for later; that
time is now. the reader now supports jumps forward (but not backwards,
and I don't know how likely it is we'll ever see this)

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

gp2040ce_bintools/storage.py

@@ -114,9 +114,13 @@ def convert_uf2_to_binary(uf2: bytearray) -> bytearray:
         if block_count != len(uf2) // 512:
             raise ValueError(f"inconsistent block count in reading UF2, got {block_count}, expected {len(uf2) // 512}!")
 
-        # the UF2 is indexed, which we could convert to binary with padding 0s, but we don't yet
-        if old_uf2_addr and (uf2_addr != old_uf2_addr + 256):
-            raise ValueError("segmented UF2 files are not yet supported!")
+        if old_uf2_addr and (uf2_addr >= old_uf2_addr + bytes_):
+            # the new binary content is not immediately after what we wrote, it's further ahead, so pad
+            # the difference
+            binary += bytearray(b'\x00' * (uf2_addr - (old_uf2_addr + bytes_)))
+        elif old_uf2_addr and (uf2_addr < old_uf2_addr + bytes_):
+            # this is seeking backwards which we don't see yet
+            raise NotImplementedError("going backwards in binary files is not yet supported")
 
         binary += content[0:bytes_]
         old_uf2_addr = uf2_addr

tests/test_storage.py

@@ -12,6 +12,7 @@ import pytest
 from decorator import decorator
 
 import gp2040ce_bintools.storage as storage
+from gp2040ce_bintools.builder import concatenate_firmware_and_storage_files
 
 HERE = os.path.dirname(os.path.abspath(__file__))
 
@@ -187,6 +188,36 @@ def test_malformed_uf2(whole_board_with_board_config_dump):
         storage.convert_uf2_to_binary(uf2 + uf2)
 
 
+def test_read_created_uf2(tmp_path, firmware_binary, config_binary):
+    """Test that we read a UF2 with disjoint segments."""
+    tmp_file = os.path.join(tmp_path, 'concat.uf2')
+    firmware_file = os.path.join(HERE, 'test-files', 'test-firmware.bin')
+    config_file = os.path.join(HERE, 'test-files', 'test-config.bin')
+    concatenate_firmware_and_storage_files(firmware_file, binary_board_config_filename=config_file,
+                                           binary_user_config_filename=config_file,
+                                           combined_filename=tmp_file)
+    with open(tmp_file, 'rb') as file:
+        content = file.read()
+    assert len(content) == (math.ceil(len(firmware_binary)/256) * 512 +
+                            math.ceil(storage.STORAGE_SIZE/256) * 512 * 2)
+
+    binary = storage.convert_uf2_to_binary(content)
+    # the converted binary should be aligned properly and of the right size
+    assert len(binary) == 2 * 1024 * 1024
+    assert binary[-16384-4:-16384] == storage.FOOTER_MAGIC
+    assert binary[-4:] == storage.FOOTER_MAGIC
+    user_storage = storage.get_user_storage_section(binary)
+    footer_size, _, _ = storage.get_config_footer(user_storage)
+    assert footer_size == 3309
+
+
+def test_cant_read_out_of_order_uf2():
+    """Test that we currently raise an exception at out of order UF2s until we fix it."""
+    uf2 = storage.convert_binary_to_uf2([(0x1000, b'\x11'), (0, b'\x11')])
+    with pytest.raises(NotImplementedError):
+        storage.convert_uf2_to_binary(uf2)
+
+
 @with_pb2s
 def test_serialize_config_with_footer(storage_dump, config_binary):
     """Test that reserializing a read in config matches the original.