From 294f47be0139fab0e10a08ab2cf0b38356c0c212 Mon Sep 17 00:00:00 2001
From: Paulus Schoutsen <balloob@gmail.com>
Date: Sat, 4 Jul 2026 03:15:30 -0400
Subject: [PATCH] fix: emit NFC config packets last so firmware keeps
 flash/data_extended (M4)

Python emitted the NFC packet (0x2A) before flash_config (0x2B) and
data_extended (0x2C). Firmware has no case 0x2A and its default case skips
straight to the CRC, so any config containing NFC entries silently lost
flash_config and data_extended on device load. Emit NFC after every packet
type the firmware understands.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JRrm95f1qNZzDM9r2SB6KW
---
 src/opendisplay/protocol/config_serializer.py | 16 +++--
 tests/unit/test_nfc_packet_ordering.py        | 69 +++++++++++++++++++
 2 files changed, 79 insertions(+), 6 deletions(-)
 create mode 100644 tests/unit/test_nfc_packet_ordering.py

diff --git a/src/opendisplay/protocol/config_serializer.py b/src/opendisplay/protocol/config_serializer.py
index 7a077b7..8e48ff3 100644
--- a/src/opendisplay/protocol/config_serializer.py
+++ b/src/opendisplay/protocol/config_serializer.py
@@ -612,12 +612,6 @@ def serialize_config(config: GlobalConfig) -> bytes:
         packet_data += bytes([i, PACKET_TYPE_PASSIVE_BUZZER])
         packet_data += serialize_passive_buzzer(bz)
 
-    for i, nfc in enumerate(config.nfc_configs):
-        if i >= 4:
-            break
-        packet_data += bytes([i, PACKET_TYPE_NFC_CONFIG])
-        packet_data += serialize_nfc_config(nfc)
-
     for i, flash in enumerate(config.flash_configs):
         if i >= 4:
             break
@@ -628,6 +622,16 @@ def serialize_config(config: GlobalConfig) -> bytes:
         packet_data += bytes([0, PACKET_TYPE_DATA_EXTENDED])
         packet_data += serialize_data_extended(config.data_extended)
 
+    # NFC (0x2A) is emitted LAST: firmware has no case 0x2A and its default case
+    # skips straight to the CRC, so any packet that follows an NFC entry (e.g.
+    # flash_config 0x2B or data_extended 0x2C) would be silently dropped on the
+    # device. Keeping NFC after every packet firmware understands avoids that.
+    for i, nfc in enumerate(config.nfc_configs):
+        if i >= 4:
+            break
+        packet_data += bytes([i, PACKET_TYPE_NFC_CONFIG])
+        packet_data += serialize_nfc_config(nfc)
+
     # Validate size (max 4096 bytes including wrapper and CRC)
     total_size = len(packet_data) + 2  # +2 for CRC
     if total_size > 4096:
diff --git a/tests/unit/test_nfc_packet_ordering.py b/tests/unit/test_nfc_packet_ordering.py
new file mode 100644
index 0000000..6e4860d
--- /dev/null
+++ b/tests/unit/test_nfc_packet_ordering.py
@@ -0,0 +1,69 @@
+"""Test that NFC (0x2A) packets are emitted after packets firmware parses (M4)."""
+
+from __future__ import annotations
+
+from opendisplay.models.config import (
+    DataExtended,
+    FlashConfig,
+    GlobalConfig,
+    ManufacturerData,
+    NfcConfig,
+    PowerOption,
+    SystemConfig,
+)
+from opendisplay.protocol.config_parser import _get_packet_size
+from opendisplay.protocol.config_serializer import (
+    PACKET_TYPE_DATA_EXTENDED,
+    PACKET_TYPE_FLASH_CONFIG,
+    PACKET_TYPE_NFC_CONFIG,
+    serialize_config,
+)
+
+
+def _packet_type_order(blob: bytes) -> list[int]:
+    """Return the packet-type IDs in the serialized TLV stream, in order."""
+    data = blob[3:-2]  # strip 3-byte wrapper header and 2-byte CRC
+    order: list[int] = []
+    off = 0
+    while off < len(data) - 1:
+        ptype = data[off + 1]
+        size = _get_packet_size(ptype)
+        if size is None:
+            break
+        order.append(ptype)
+        off += 2 + size
+    return order
+
+
+def test_nfc_emitted_after_flash_and_data_extended() -> None:
+    config = GlobalConfig(
+        system=SystemConfig(ic_type=0, communication_modes=0, device_flags=0, pwr_pin=0xFF, reserved=b"\x00" * 15),
+        manufacturer=ManufacturerData(manufacturer_id=0, board_type=0, board_revision=0, reserved=b"\x00" * 6),
+        power=PowerOption(
+            power_mode=0,
+            battery_capacity_mah=b"\x00\x00\x00",
+            sleep_timeout_ms=0,
+            tx_power=0,
+            sleep_flags=0,
+            battery_sense_pin=0xFF,
+            battery_sense_enable_pin=0xFF,
+            battery_sense_flags=0,
+            capacity_estimator=0,
+            voltage_scaling_factor=0,
+            deep_sleep_current_ua=0,
+            deep_sleep_time_seconds=0,
+            reserved=b"\x00" * 10,
+        ),
+        nfc_configs=[NfcConfig.from_bytes(bytes(32))],
+        flash_configs=[FlashConfig.from_bytes(bytes(32))],
+        data_extended=DataExtended(),
+    )
+
+    order = _packet_type_order(serialize_config(config))
+
+    assert PACKET_TYPE_NFC_CONFIG in order
+    assert PACKET_TYPE_FLASH_CONFIG in order
+    assert PACKET_TYPE_DATA_EXTENDED in order
+    nfc_pos = order.index(PACKET_TYPE_NFC_CONFIG)
+    assert nfc_pos > order.index(PACKET_TYPE_FLASH_CONFIG)
+    assert nfc_pos > order.index(PACKET_TYPE_DATA_EXTENDED)