Implement E and I commands

As with the other commands that take a range of flash sectors, the end
is optional.  I returns None if the sectors are blank, or an offset and
value if the sectors are not blank.

alpaca_isp/__init__.py

@@ -217,6 +217,38 @@ class LPC:
         """
         self._writeline("G {} {}\r\n".format(address, mode).encode("utf-8"))
 
+    def erase(self, start, end=None):
+        """Erase the given flash sector(s)
+
+        If end is not specified, only the start sector is erased.
+        """
+        if end is None:
+            end = start
+        self._send_command("E {} {}\r\n".format(start, end).encode("utf-8"))
+
+    def blank_check(self, start, end=None):
+        """Check if the given flash sectors are blank
+
+        If end is not specified, only the start sector is checked.
+
+        Returns None if the sector is blank, or a tuple containing the offset
+        and value of the first non-blank word location if the sector is not
+        blank.  If CRP is enabled, the offset and value are always reported as
+        zero.
+        """
+        if end is None:
+            end = start
+        try:
+            self._send_command("I {} {}\r\n".format(start, end).encode(
+                "utf-8"))
+        except ISPError as e:
+            # Return a tuple for SECTOR_NOT_BLANK
+            if e.args[0][0] == ReturnCode.SECTOR_NOT_BLANK:
+                offset = int(self._readline().strip())
+                value = int(self._readline().strip())
+                return (offset, value)
+            raise
+
 
 class ReturnCode(Enum):
     """LPC ISP return codes