fix the mistake of calling modbus API before T35 timer complate initialization

FreeModbus/modbus/include/mb_m.h

@@ -172,6 +172,18 @@ eMBErrorCode    eMBMasterEnable( void );
  */
 eMBErrorCode    eMBMasterDisable( void );
 
+/*! \ingroup modbus
+ * \brief Check the Modbus Master protocol stack has established or not.
+ *
+ * This function must be called and check the return value before calling
+ * any other functions.
+ *
+ * \return If the protocol stack has been established or not
+ *  TRUE.  the protocol stack has established
+ *  FALSE. the protocol stack hasn't established
+ */
+BOOL            eMBMasterIsEstablished( void );
+
 /*! \ingroup modbus
  * \brief The main pooling loop of the Modbus Master protocol stack.
  *

FreeModbus/modbus/mb_m.c

@@ -71,7 +71,8 @@ static enum
 {
     STATE_ENABLED,
     STATE_DISABLED,
-    STATE_NOT_INITIALIZED
+    STATE_NOT_INITIALIZED,
+	STATE_ESTABLISHED,
 } eMBState = STATE_NOT_INITIALIZED;
 
 /* Functions pointer which are initialized in eMBInit( ). Depending on the
@@ -233,7 +234,7 @@ eMBMasterDisable( void )
 {
     eMBErrorCode    eStatus;
 
-    if( eMBState == STATE_ENABLED )
+    if(( eMBState == STATE_ENABLED ) || ( eMBState == STATE_ESTABLISHED))
     {
         pvMBMasterFrameStopCur(  );
         eMBState = STATE_DISABLED;
@@ -250,6 +251,20 @@ eMBMasterDisable( void )
     return eStatus;
 }
 
+BOOL
+eMBMasterIsEstablished( void )
+{
+    if(eMBState == STATE_ESTABLISHED)
+    {
+        return TRUE;
+    }
+    else
+    {
+        return FALSE;
+    }
+}
+
+
 eMBErrorCode
 eMBMasterPoll( void )
 {
@@ -265,7 +280,7 @@ eMBMasterPoll( void )
     eMBMasterErrorEventType errorType;
 
     /* Check if the protocol stack is ready. */
-    if( eMBState != STATE_ENABLED )
+    if(( eMBState != STATE_ENABLED ) && ( eMBState != STATE_ESTABLISHED))
     {
         return MB_EILLSTATE;
     }
@@ -277,6 +292,7 @@ eMBMasterPoll( void )
         switch ( eEvent )
         {
         case EV_MASTER_READY:
+		    eMBState = STATE_ESTABLISHED;
             break;
 
         case EV_MASTER_FRAME_RECEIVED: