Flush serialport output before every AT command

lib/biju/hayes.rb

@@ -36,6 +36,7 @@ module Biju
       full_command = [command, (command_args.empty? ? nil : command_args)]
         .compact.join('=') + "\r\n"
 
+      modem.flush
       modem.write(full_command)
       answer = hayes_to_obj(modem.wait(length: full_command.length))
 

lib/biju/modem.rb

@@ -22,10 +22,14 @@ module Biju
 
     def_delegators :connection, :close, :write
 
-    def wait(length: 0)
+    def flush
+      wait(length: 0, timeout: 0)
+    end
+
+    def wait(length: 0, timeout: 10)
       buffer = ''
-      Timeout.timeout(10) do
-        while IO.select([connection], [], [], 0.50) || buffer.length < length
+      Timeout.timeout(timeout) do
+        while IO.select([connection], [], [], 0.25) || buffer.length < length
           buffer << connection.getc.chr
         end
       end