AP_Logger: allow for new log msgs in Replay

this makes replay tuning and code testing much easier as up to 10 new
log messages can be added in the replay code

libraries/AP_Logger/AP_Logger.cpp

@@ -57,6 +57,14 @@ extern const AP_HAL::HAL& hal;
 # endif
 #endif
 
+// when adding new msgs we start at a different index in replay
+#if APM_BUILD_TYPE(APM_BUILD_Replay)
+#define LOGGING_FIRST_DYNAMIC_MSGID REPLAY_LOG_NEW_MSG_MAX
+#else
+#define LOGGING_FIRST_DYNAMIC_MSGID 254
+#endif
+
+
 const AP_Param::GroupInfo AP_Logger::var_info[] = {
     // @Param: _BACKEND_TYPE
     // @DisplayName: AP_Logger Backend Storage type
@@ -1078,12 +1086,6 @@ AP_Logger::log_write_fmt *AP_Logger::msg_fmt_for_name(const char *name, const ch
         }
     }
 
-#if APM_BUILD_TYPE(APM_BUILD_Replay)
-    // don't allow for new msg types during replay. We will be able to
-    // support these eventually, but for now they cause corruption
-    return nullptr;
-#endif
-
     f = (struct log_write_fmt *)calloc(1, sizeof(*f));
     if (f == nullptr) {
         // out of memory
@@ -1198,8 +1200,9 @@ bool AP_Logger::msg_type_in_use(const uint8_t msg_type) const
 // find a free message type
 int16_t AP_Logger::find_free_msg_type() const
 {
+    const uint8_t start = LOGGING_FIRST_DYNAMIC_MSGID;
     // avoid using 255 here; perhaps we want to use it to extend things later
-    for (uint16_t msg_type=254; msg_type>0; msg_type--) { // more likely to be free at end
+    for (uint16_t msg_type=start; msg_type>0; msg_type--) { // more likely to be free at end
         if (! msg_type_in_use(msg_type)) {
             return msg_type;
         }

libraries/AP_Logger/AP_Logger.h

@@ -48,6 +48,12 @@
 #define HAL_LOGGER_FILE_CONTENTS_ENABLED HAL_LOGGING_FILESYSTEM_ENABLED
 #endif
 
+// range of IDs to allow for new messages during replay. It is very
+// useful to be able to add new messages during a replay, but we need
+// to avoid colliding with existing messages
+#define REPLAY_LOG_NEW_MSG_MAX 230
+#define REPLAY_LOG_NEW_MSG_MIN 220
+
 #include <AC_PID/AC_PID.h>
 #include <AP_HAL/AP_HAL.h>
 #include <AP_AHRS/AP_AHRS.h>

libraries/AP_Logger/AP_Logger_Backend.cpp

@@ -172,8 +172,10 @@ void AP_Logger_Backend::WriteMoreStartupMessages()
 bool AP_Logger_Backend::Write_Emit_FMT(uint8_t msg_type)
 {
 #if APM_BUILD_TYPE(APM_BUILD_Replay)
-    // sure, sure we did....
-    return true;
+    if (msg_type < REPLAY_LOG_NEW_MSG_MIN || msg_type > REPLAY_LOG_NEW_MSG_MAX) {
+        // don't re-emit FMU msgs unless they are in the replay range
+        return true;
+    }
 #endif
 
     // get log structure from front end: