text: import esp
  
  
  class FlashBdev:
  
      SEC_SIZE = 4096
      RESERVED_SECS = 1
      START_SEC = esp.flash_user_start() // SEC_SIZE + RESERVED_SECS
      NUM_BLK = 0x6B - RESERVED_SECS
  
      def __init__(self, blocks=NUM_BLK):
          self.blocks = blocks
  
      def readblocks(self, n, buf, off=0):
          # print("readblocks(%s, %x(%d), %d)" % (n, id(buf), len(buf), off))
          esp.flash_read((n + self.START_SEC) * self.SEC_SIZE + off, buf)
  
      def writeblocks(self, n, buf, off=None):
          # print("writeblocks(%s, %x(%d), %d)" % (n, id(buf), len(buf), off))
          # assert len(buf) <= self.SEC_SIZE, len(buf)
          if off is None:
              esp.flash_erase(n + self.START_SEC)
              off = 0
          esp.flash_write((n + self.START_SEC) * self.SEC_SIZE + off, buf)
  
      def ioctl(self, op, arg):
          # print("ioctl(%d, %r)" % (op, arg))
          if op == 4:  # MP_BLOCKDEV_IOCTL_BLOCK_COUNT
              return self.blocks
          if op == 5:  # MP_BLOCKDEV_IOCTL_BLOCK_SIZE
              return self.SEC_SIZE
          if op == 6:  # MP_BLOCKDEV_IOCTL_BLOCK_ERASE
              esp.flash_erase(arg + self.START_SEC)
              return 0
  
  
  size = esp.flash_size()
  if size < 1024 * 1024:
      bdev = None
  else:
      # 20K at the flash end is reserved for SDK params storage
      bdev = FlashBdev((size - 20480) // FlashBdev.SEC_SIZE - FlashBdev.START_SEC)
  