diff -r d92d201d22e1 -r 9101a72a1da0 svghmi/svghmi.c
--- a/svghmi/svghmi.c	Wed Dec 18 13:31:22 2019 +0100
+++ b/svghmi/svghmi.c	Fri Jan 10 13:15:07 2020 +0100
@@ -257,16 +257,19 @@
     subscribe = 2
 } cmd_from_JS;
 
+// Returns :
+//   0 is OK, <0 is error, 1 is heartbeat
 int svghmi_recv_dispatch(uint32_t size, const uint8_t *ptr){
     const uint8_t* cursor = ptr + HMI_HASH_SIZE;
     const uint8_t* end = ptr + size;
 
+    int was_hearbeat = 0;
 
     /* match hmitree fingerprint */
     if(size <= HMI_HASH_SIZE || memcmp(ptr, hmi_hash, HMI_HASH_SIZE) != 0)
     {
         printf("svghmi_recv_dispatch MISMATCH !!\n");
-        return EINVAL;
+        return -EINVAL;
     }
 
     while(cursor < end)
@@ -279,6 +282,9 @@
             {
                 uint32_t index = *(uint32_t*)(cursor);
                 uint8_t const *valptr = cursor + sizeof(uint32_t);
+                
+                if(index == heartbeat_index)
+                    was_hearbeat = 1;
 
                 if(index < HMI_ITEM_COUNT)
                 {
@@ -344,6 +350,6 @@
         }
         cursor += progress;
     }
-    return 0;
-}
-
+    return was_hearbeat;
+}
+