old_contents: import uos
  import network
  from flashbdev import bdev
  
  
  def wifi():
      import ubinascii
  
      ap_if = network.WLAN(network.AP_IF)
      essid = b"MicroPython-%s" % ubinascii.hexlify(ap_if.config("mac")[-3:])
      ap_if.config(essid=essid, authmode=network.AUTH_WPA_WPA2_PSK, password=b"micropythoN")
  
  
  def check_bootsec():
      buf = bytearray(bdev.SEC_SIZE)
      bdev.readblocks(0, buf)
      empty = True
      for b in buf:
          if b != 0xFF:
              empty = False
              break
      if empty:
          return True
      fs_corrupted()
  
  
  def fs_corrupted():
      import time
  
      while 1:
          print(
              """\
  The filesystem starting at sector %d with size %d sectors appears to
  be corrupted. If you had important data there, you may want to make a flash
  snapshot to try to recover it. Otherwise, perform factory reprogramming
  of MicroPython firmware (completely erase flash, followed by firmware
  programming).
  """
              % (bdev.START_SEC, bdev.blocks)
          )
          time.sleep(3)
  
  
  def setup():
      check_bootsec()
      print("Performing initial setup")
      wifi()
      uos.VfsLfs2.mkfs(bdev)
      vfs = uos.VfsLfs2(bdev)
      uos.mount(vfs, "/")
      with open("boot.py", "w") as f:
          f.write(
              """\
  # This file is executed on every boot (including wake-boot from deepsleep)
  #import esp
  #esp.osdebug(None)
  import uos, machine
  #uos.dupterm(None, 1) # disable REPL on UART(0)
  import gc
  #import webrepl
  #webrepl.start()
  gc.collect()
  """
          )
      return vfs
  
new_contents: import uos
  import network
  from flashbdev import bdev
  
  
  def wifi():
      import ubinascii
  
      ap_if = network.WLAN(network.AP_IF)
      essid = b"MicroPython-%s" % ubinascii.hexlify(ap_if.config("mac")[-3:])
      ap_if.config(essid=essid, authmode=network.AUTH_WPA_WPA2_PSK, password=b"micropythoN")
  
  
  def check_bootsec():
      buf = bytearray(bdev.SEC_SIZE)
      bdev.readblocks(0, buf)
      empty = True
      for b in buf:
          if b != 0xFF:
              empty = False
              break
      if empty:
          return True
      fs_corrupted()
  
  
  def fs_corrupted():
      import time
  
      while 1:
          print(
              """\
  The filesystem starting at sector %d with size %d sectors looks corrupt.
  You may want to make a flash snapshot and try to recover it. Otherwise,
  format it with uos.VfsLfs2.mkfs(bdev), or completely erase the flash and
  reprogram MicroPython.
  """
              % (bdev.start_sec, bdev.blocks)
          )
          time.sleep(3)
  
  
  def setup():
      check_bootsec()
      print("Performing initial setup")
      wifi()
      uos.VfsLfs2.mkfs(bdev)
      vfs = uos.VfsLfs2(bdev)
      uos.mount(vfs, "/")
      with open("boot.py", "w") as f:
          f.write(
              """\
  # This file is executed on every boot (including wake-boot from deepsleep)
  #import esp
  #esp.osdebug(None)
  import uos, machine
  #uos.dupterm(None, 1) # disable REPL on UART(0)
  import gc
  #import webrepl
  #webrepl.start()
  gc.collect()
  """
          )
      return vfs
  
subject: Fix fs_corrupted() to use start_sec not START_SEC.