diff -r 63bef67e812b -r fdb85a806585 include/ecrt.h
--- a/include/ecrt.h	Thu Sep 06 14:40:10 2012 +0200
+++ b/include/ecrt.h	Thu Sep 06 18:28:57 2012 +0200
@@ -39,6 +39,14 @@
  * request a master, to map process data, to communicate with slaves via CoE
  * and to configure and activate the bus.
  *
+ * Changed since 1.5:
+ *
+ * - Added redundancy_active flag to ec_domain_state_t.
+ * - Added ecrt_master_link_state() method and ec_master_link_state_t to query
+ *   the state of a redundant link.
+ * - Added the EC_HAVE_REDUNDANCY define, to check, if the interface contains
+ *   redundancy features.
+ *
  * Changes in version 1.5:
  *
  * - Added the distributed clocks feature and the respective method
@@ -119,6 +127,17 @@
  */
 #define ECRT_VERSION_MAGIC ECRT_VERSION(ECRT_VER_MAJOR, ECRT_VER_MINOR)
 
+/******************************************************************************
+ * Feature flags
+ *****************************************************************************/
+
+/** Defined, if the redundancy features are available.
+ *
+ * I. e. if the \a redundancy_active flag in ec_domain_state_t and the
+ * ecrt_master_link_state() method are available.
+ */
+#define EC_HAVE_REDUNDANCY
+
 /*****************************************************************************/
 
 /** End of list marker.
@@ -179,7 +198,8 @@
  * \see ecrt_master_state().
  */
 typedef struct {
-    unsigned int slaves_responding; /**< Number of slaves in the bus. */
+    unsigned int slaves_responding; /**< Sum of responding slaves on all
+                                      Ethernet devices. */
     unsigned int al_states : 4; /**< Application-layer states of all slaves.
                                   The states are coded in the lower 4 bits.
                                   If a bit is set, it means that at least one
@@ -189,11 +209,36 @@
                                   - Bit 1: \a PREOP
                                   - Bit 2: \a SAFEOP
                                   - Bit 3: \a OP */
-    unsigned int link_up : 1; /**< \a true, if the network link is up. */
+    unsigned int link_up : 1; /**< \a true, if at least one Ethernet link is
+                                up. */
 } ec_master_state_t;
 
 /*****************************************************************************/
 
+/** Redundant link state.
+ *
+ * This is used for the output parameter of ecrt_master_link_state().
+ *
+ * \see ecrt_master_link_state().
+ */
+typedef struct {
+    unsigned int slaves_responding; /**< Sum of responding slaves on the given
+                                      link. */
+    unsigned int al_states : 4; /**< Application-layer states of the slaves on
+                                  the given link.  The states are coded in the
+                                  lower 4 bits.  If a bit is set, it means
+                                  that at least one slave in the bus is in the
+                                  corresponding state:
+                                  - Bit 0: \a INIT
+                                  - Bit 1: \a PREOP
+                                  - Bit 2: \a SAFEOP
+                                  - Bit 3: \a OP */
+    unsigned int link_up : 1; /**< \a true, if the given Ethernet link is up.
+                               */
+} ec_master_link_state_t;
+
+/*****************************************************************************/
+
 /** Slave configuration state.
  *
  * This is used as an output parameter of ecrt_slave_config_state().
@@ -304,6 +349,7 @@
 typedef struct {
     unsigned int working_counter; /**< Value of the last working counter. */
     ec_wc_state_t wc_state; /**< Working counter interpretation. */
+    unsigned int redundancy_active; /**< Redundant link is in use. */
 } ec_domain_state_t;
 
 /*****************************************************************************/
@@ -848,12 +894,29 @@
 /** Reads the current master state.
  *
  * Stores the master state information in the given \a state structure.
+ *
+ * This method returns a global state. For the link-specific states in a
+ * redundant bus topology, use the ecrt_master_link_state() method.
  */
 void ecrt_master_state(
         const ec_master_t *master, /**< EtherCAT master. */
         ec_master_state_t *state /**< Structure to store the information. */
         );
 
+/** Reads the current state of a redundant link.
+ *
+ * Stores the link state information in the given \a state structure.
+ *
+ * \return Zero on success, otherwise negative error code.
+ */
+int ecrt_master_link_state(
+        const ec_master_t *master, /**< EtherCAT master. */
+        unsigned int dev_idx, /**< Index of the device (0 = main device, 1 =
+                                first backup device, ...). */
+        ec_master_link_state_t *state /**< Structure to store the information.
+                                       */
+        );
+
 /** Sets the application time.
  *
  * The master has to know the application's time when operating slaves with