AP_Logger: log long MSG messages in multiple chunks

libraries/AP_Logger/AP_Logger.cpp

@@ -908,6 +908,10 @@ void AP_Logger::Write_Message(const char *message)
 {
     FOR_EACH_BACKEND(Write_Message(message));
 }
+void AP_Logger::Write_MessageChunk(uint8_t id, const char *messagechunk, uint8_t chunk_seq)
+{
+    FOR_EACH_BACKEND(Write_MessageChunk(id, messagechunk, chunk_seq));
+}
 
 void AP_Logger::Write_Mode(uint8_t mode, const ModeReason reason)
 {

libraries/AP_Logger/AP_Logger.h

@@ -262,6 +262,16 @@ public:
     void Write_Power(void);
     void Write_Radio(const mavlink_radio_t &packet);
     void Write_Message(const char *message);
+    // support for multi-chunk messages:
+    uint8_t get_MSG_id() {
+        uint8_t ret = ++MSG_id;
+        if (ret > 0) {
+            return ret;
+        }
+        return ++MSG_id;
+    }
+    void Write_MessageChunk(uint8_t id, const char *messagechunk, uint8_t chunk_seq);
+
     void Write_MessageF(const char *fmt, ...);
     void Write_Compass();
     void Write_Mode(uint8_t mode, const ModeReason reason);
@@ -616,6 +626,9 @@ private:
     void log_file_content(FileContent &file_content, const char *filename);
     void file_content_update(FileContent &file_content);
 #endif
+
+    // support for multi-chunk messages:
+    uint8_t MSG_id;
 };
 
 namespace AP {

libraries/AP_Logger/AP_Logger_Backend.h

@@ -139,6 +139,7 @@ public:
     }
     bool Write_Message(const char *message);
     bool Write_MessageF(const char *fmt, ...);
+    bool Write_MessageChunk(uint8_t id, const char *messagechunk, uint8_t chunk_seq);
     bool Write_Mission_Cmd(const AP_Mission &mission,
                            const AP_Mission::Mission_Command &cmd,
                            LogMessages id);
@@ -275,6 +276,7 @@ private:
     bool emit_format_for_type(LogMessages a_type);
     Bitmask<256> _formats_written;
 
+    uint8_t msg_id;  // the ID of the next MSG message that will be logged
 };
 
 #endif  // HAL_LOGGING_ENABLED

libraries/AP_Logger/LogFile.cpp

@@ -339,13 +339,37 @@ bool AP_Logger_Backend::Write_EntireMission()
 // Write a text message to the log
 bool AP_Logger_Backend::Write_Message(const char *message)
 {
-    struct log_Message pkt{
-        LOG_PACKET_HEADER_INIT(LOG_MESSAGE_MSG),
+    // i==0 here means we log an empty string if it is passed in:
+    const uint8_t id = AP::logger().get_MSG_id();  // there is a race condition on this ID; if a thread logs a message at the same time as the main thread then we can re-use this
+
+    uint8_t chunk_seq = 0;
+    for (uint8_t i=0; i == 0 || i<strlen(message); i += 64, chunk_seq++) {
+        const bool success = Write_MessageChunk(id, &message[i], chunk_seq);
+        if (i == 0 && !success) {
+            return false;
+        }
+    }
+    return true;
+}
+bool AP_Logger_Backend::Write_MessageChunk(uint8_t id, const char *messagechunk, uint8_t chunk_seq)
+{
+    struct log_MSG pkt{
+        LOG_PACKET_HEADER_INIT(LOG_MSG_MSG),
         time_us : AP_HAL::micros64(),
+        id           : id,
+        chunk_seq : chunk_seq,
         msg  : {}
     };
-    strncpy_noterm(pkt.msg, message, sizeof(pkt.msg));
-    return WriteCriticalBlock(&pkt, sizeof(pkt));
+    const uint16_t remaining = strlen(messagechunk);
+    strncpy_noterm(pkt.msg, messagechunk, MIN(sizeof(pkt.msg), remaining));
+    // result comes from success writing the first chunk; this
+    // prevents trying to write out the front of a message
+    // repeatedly.
+    const bool success = WriteCriticalBlock(&pkt, sizeof(pkt));
+    if (chunk_seq == 0) {
+        return success;
+    }
+    return true;
 }
 
 void AP_Logger::Write_Power(void)

libraries/AP_Logger/LogStructure.h

@@ -246,9 +246,11 @@ struct PACKED log_Error {
 };
 
 
-struct PACKED log_Message {
+struct PACKED log_MSG {
     LOG_PACKET_HEADER;
     uint64_t time_us;
+    uint8_t id;
+    uint8_t chunk_seq;
     char msg[64];
 };
 
@@ -813,6 +815,8 @@ struct PACKED log_VER {
 // @LoggerMessage: MSG
 // @Description: Textual messages
 // @Field: TimeUS: Time since system startup
+// @Field: ID: identifier for chunks making up a message
+// @Field: Seq: chunk sequence number within message identified by ID
 // @Field: Message: message text
 
 // @LoggerMessage: MULT
@@ -1154,8 +1158,8 @@ struct PACKED log_VER {
     { LOG_PARAMETER_MSG, sizeof(log_Parameter), \
      "PARM", "QNff",        "TimeUS,Name,Value,Default", "s---", "F---"  },       \
 LOG_STRUCTURE_FROM_GPS \
-    { LOG_MESSAGE_MSG, sizeof(log_Message), \
-      "MSG",  "QZ",     "TimeUS,Message", "s-", "F-"}, \
+    { LOG_MSG_MSG, sizeof(log_MSG), \
+      "MSG",  "QBBZ",     "TimeUS,ID,Seq,Message", "s---", "F---"}, \
     { LOG_RCIN_MSG, sizeof(log_RCIN), \
       "RCIN",  "QHHHHHHHHHHHHHH",     "TimeUS,C1,C2,C3,C4,C5,C6,C7,C8,C9,C10,C11,C12,C13,C14", "sYYYYYYYYYYYYYY", "F--------------", true }, \
     { LOG_RCI2_MSG, sizeof(log_RCI2), \
@@ -1271,7 +1275,7 @@ enum LogMessages : uint8_t {
     LOG_PARAMETER_MSG = 32,
     LOG_IDS_FROM_NAVEKF2,
     LOG_IDS_FROM_NAVEKF3,
-    LOG_MESSAGE_MSG,
+    LOG_MSG_MSG,
     LOG_RCIN_MSG,
     LOG_RCI2_MSG,
     LOG_RCOUT_MSG,

libraries/AP_Logger/examples/AP_Logger_AllTypes/AP_Logger_AllTypes.cpp

@@ -80,8 +80,8 @@ static const struct LogStructure log_structure[] = {
       "s---------",
       "F---------"
     },
-    { LOG_MESSAGE_MSG,
-      sizeof(log_Message),
+    { LOG_MSG_MSG,
+      sizeof(log_MSG),
       "MSG",
       "QZ",
       "TimeUS,Message",