The error response returned for some packets includes a two character
error number. That number is not well defined.
-@cindex empty response, to unsupported packets
+@cindex empty response, for unsupported packets
For any @var{command} not supported by the stub, an empty response
(@samp{$#00}) should be returned. That way it is possible to extend the
protocol. A newer @value{GDBN} can tell if a packet is supported based