fix firmware selection logic for backend compatibility.

Signed-off-by: Jos Verlinde <Jos_Verlinde@hotmail.com>

Author: Josverl

mpflash/cli_flash.py

@@ -205,6 +205,11 @@ def _create_worklist_or_fail(*create_args, **create_kwargs) -> FlashTaskList:
                 "Try specifying both --board and --serial, or use '--serial *' to auto-detect ports."
             ) from None
 
+    # Track whether the board was explicitly provided on CLI.
+    # This prevents mixed auto-detected board/variant state from multiple
+    # connected devices when only --serial was specified.
+    board_specified = kwargs.get("board") is not None
+
     # version to versions, board to boards
     kwargs["versions"] = [kwargs.pop("version")] if kwargs["version"] is not None else []
     if kwargs["board"] is None:
@@ -249,8 +254,8 @@ def _create_worklist_or_fail(*create_args, **create_kwargs) -> FlashTaskList:
             ignore=params.ignore,
             bluetooth=params.bluetooth,
         )
-        if variants and len(variants) >= 1:
-            params.variant = variants[0]
+        # Do not auto-pick a variant from a set of connected boards; this can
+        # leak a variant from another attached device (e.g. ESP32 SPIRAM).
         if params.boards == []:
             # No MicroPython boards detected, but it could be unflashed or in bootloader mode
             # Ask for serial port and board_id to flash
@@ -323,6 +328,26 @@ def _create_worklist_or_fail(*create_args, **create_kwargs) -> FlashTaskList:
             include_ports=params.serial,
             ignore_ports=params.ignore,
         )
+    elif params.versions[0] and params.serial and not board_specified:
+        # Serial port(s) were explicitly provided, but board_id was not.
+        # Build tasks from per-port auto-detection to avoid cross-device board/variant mixing.
+        # IMPORTANT: honor explicit serial targets exactly. Do not broaden with
+        # include/ignore set logic, otherwise unrelated attached boards can leak
+        # into this run.
+        specified = [p for p in params.serial if p and p != "*"]
+        ignored = set(params.ignore or [])
+        comports = [p for p in specified if p not in ignored]
+        if not comports:
+            serial_filter = ", ".join(params.serial)
+            raise click.UsageError(
+                f"No serial ports matched: {serial_filter}. Check the port name, "
+                "or use '--serial *' to auto-detect."
+            )
+        connected_comports = [MPRemoteBoard(port, update=True) for port in comports]
+        tasks = _create_worklist_or_fail(
+            params.versions[0],
+            connected_comports=connected_comports,
+        )
     elif params.versions[0] and params.boards and params.serial:
         # Manual specification of serial ports + board
         comports = filtered_comports(

mpflash/flash/__init__.py

@@ -16,6 +16,7 @@
 
 from mpflash.common import BootloaderMethod, FlashMethod
 from mpflash.config import config
+from mpflash.downloaded import find_downloaded_firmware
 from mpflash.errors import MPFlashError
 from mpflash.logger import log
 
@@ -52,10 +53,76 @@ def flash_tasks(
     **kwargs,
 ):
     """Flash every entry in ``tasks`` and return the updated boards."""
+
+    def _pick_backend_compatible_firmware(task, fw_info):
+        """Pick a firmware image matching the explicit backend's supported formats."""
+        if fw_info is None:
+            return None
+
+        requested_name = _resolve_backend_name(method)
+        if not requested_name:
+            return fw_info
+
+        backend = get_backend(requested_name)
+        if backend is None or not backend.supported_formats:
+            return fw_info
+
+        current_suffix = Path(fw_info.firmware_file).suffix.lower()
+        if current_suffix in backend.supported_formats:
+            return fw_info
+
+        # Fast path: if a same-stem file with a backend-supported extension
+        # exists next to the selected firmware, use it directly.
+        selected_path = config.firmware_folder / fw_info.firmware_file
+        for suffix in backend.supported_formats:
+            sibling = selected_path.with_suffix(suffix)
+            if sibling.exists():
+                rel = sibling.relative_to(config.firmware_folder).as_posix()
+                log.info(
+                    f"Using {requested_name} compatible sibling firmware {rel} "
+                    f"instead of {fw_info.firmware_file} for {task.board.board} on {task.board.serialport}"
+                )
+                fw_info.firmware_file = rel
+                return fw_info
+
+        board = task.board
+        detected_board_id = f"{board.board}-{board.variant}" if board.variant else board.board
+        board_ids = [getattr(fw_info, "board_id", ""), detected_board_id]
+
+        candidates = []
+        seen_files = set()
+        for bid in board_ids:
+            if not bid:
+                continue
+            # First prefer exact port match, then broaden to any port.
+            for cand in find_downloaded_firmware(
+                board_id=bid,
+                version=fw_info.version,
+                port=board.port,
+                custom=bool(fw_info.custom),
+            ) + find_downloaded_firmware(
+                board_id=bid,
+                version=fw_info.version,
+                port="",
+                custom=bool(fw_info.custom),
+            ):
+                if cand.firmware_file not in seen_files:
+                    seen_files.add(cand.firmware_file)
+                    candidates.append(cand)
+
+        for cand in reversed(candidates):
+            if Path(cand.firmware_file).suffix.lower() in backend.supported_formats:
+                log.info(
+                    f"Using {requested_name} compatible firmware {cand.firmware_file} "
+                    f"instead of {fw_info.firmware_file} for {board.board} on {board.serialport}"
+                )
+                return cand
+        return fw_info
+
     flashed = []
     for task in tasks:
         mcu = task.board
-        fw_info = task.firmware
+        fw_info = _pick_backend_compatible_firmware(task, task.firmware)
         if not fw_info:
             log.error(f"Firmware not found for {mcu.board} on {mcu.serialport}, skipping")
             continue