fix(esp32-c2): Enable flashing in secure download mode

Closes https://github.com/espressif/esptool/issues/895

esptool/cmds.py

@@ -466,7 +466,7 @@ def write_flash(esp, args):
     flash_end = flash_size_bytes(
         detect_flash_size(esp) if args.flash_size == "keep" else args.flash_size
     )
-    if flash_end is not None:  # Secure download mode
+    if flash_end is not None:  # Not in secure download mode
         for address, argfile in args.addr_filename:
             argfile.seek(0, os.SEEK_END)
             if address + argfile.tell() > flash_end:

esptool/targets/esp32c2.py

@@ -110,7 +110,7 @@ class ESP32C2ROM(ESP32C3ROM):
 
     def _post_connect(self):
         # ESP32C2 ECO0 is no longer supported by the flasher stub
-        if self.get_chip_revision() == 0:
+        if not self.secure_download_mode and self.get_chip_revision() == 0:
             self.stub_is_disabled = True
             self.IS_STUB = False
 

esptool/util.py

@@ -34,6 +34,8 @@ def flash_size_bytes(size):
     """Given a flash size of the type passed in args.flash_size
     (ie 512KB or 1MB) then return the size in bytes.
     """
+    if size is None:
+        return None
     if "MB" in size:
         return int(size[: size.index("MB")]) * 1024 * 1024
     elif "KB" in size: