[ambz2] Generate patched image for OTA

Author: prokoma

ltchiptool/soc/ambz2/binary.py

@@ -28,6 +28,7 @@
     Section,
 )
 from .util.models.utils import FF_32
+from .util.ota import patch_firmware_for_ota
 
 
 class AmebaZ2Binary(SocInterface, ABC):
@@ -110,6 +111,12 @@ def elf2bin(self, input: str, ota_idx: int) -> List[FirmwareBinary]:
             description="Firmware partition image for direct flashing",
             public=True,
         )
+        out_ota1_ota = FirmwareBinary(
+            location=input,
+            name="firmware_is_ota",
+            offset=ota1_offset,
+            title="Application Image for OTA",
+        )
         out_ptab = FirmwareBinary(
             location=input,
             name="part_table",
@@ -215,6 +222,10 @@ def elf2bin(self, input: str, ota_idx: int) -> List[FirmwareBinary]:
         with out_ota1.write() as f:
             ota1 = data[ota1_offset:ota1_end]
             f.write(ota1)
+        with out_ota1_ota.write() as f:
+            ota1 = data[ota1_offset:ota1_end]
+            ota1_ota = patch_firmware_for_ota(ota1)
+            f.write(ota1_ota)
         return output.group()
 
     def detect_file_type(

ltchiptool/soc/ambz2/util/models/images.py

@@ -29,6 +29,8 @@
 
 FLASH_CALIBRATION = b"\x99\x99\x96\x96\x3F\xCC\x66\xFC\xC0\x33\xCC\x03\xE5\xDC\x31\x62"
 
+IMAGE_PUBLIC_KEY_OFFSET = 32
+
 
 @dataclass
 class Image(DataStruct):

ltchiptool/soc/ambz2/util/ota.py

@@ -0,0 +1,10 @@
+#  Copyright (c) Martin Prokopič 2024-12-02
+
+from .models.images import IMAGE_PUBLIC_KEY_OFFSET
+
+
+def patch_firmware_for_ota(data: bytes) -> bytes:
+    copy = bytearray(data)
+    copy[0] ^= 0xff  # negate first signature byte
+    copy[IMAGE_PUBLIC_KEY_OFFSET] ^= 0xff  # negate first pubkey byte
+    return bytes(copy)