AP_Logger: move logger IO to a separate thread

libraries/AP_Logger/AP_Logger.cpp

@@ -27,6 +27,10 @@ extern const AP_HAL::HAL& hal;
 #endif
 #endif
 
+#ifndef HAL_LOGGING_STACK_SIZE
+#define HAL_LOGGING_STACK_SIZE 512
+#endif
+
 #ifndef HAL_LOGGING_MAV_BUFSIZE
 #define HAL_LOGGING_MAV_BUFSIZE  8
 #endif 
@@ -231,6 +235,8 @@ void AP_Logger::Init(const struct LogStructure *structures, uint8_t num_types)
 
     Prep();
 
+    start_io_thread();
+
     EnableWrites(true);
 }
 
@@ -1243,6 +1249,45 @@ int16_t AP_Logger::Write_calc_msg_len(const char *fmt) const
     return len;
 }
 
+// thread for processing IO - in general IO involves a long blocking DMA write to an SPI device
+// and the thread will sleep while this completes preventing other tasks from running, it therefore
+// is necessary to run the IO in it's own thread
+void AP_Logger::io_thread(void)
+{
+    uint32_t last_run_us = AP_HAL::micros();
+
+    while (true) {
+        uint32_t now = AP_HAL::micros();
+
+        uint32_t delay = 250U; // always have some delay
+        if (now - last_run_us < 1000) {
+            delay = MAX(1000 - (now - last_run_us), delay);
+        }
+        hal.scheduler->delay_microseconds(delay);
+
+        last_run_us = AP_HAL::micros();
+
+        FOR_EACH_BACKEND(io_timer());
+    }
+}
+
+// start the update thread
+void AP_Logger::start_io_thread(void)
+{
+    WITH_SEMAPHORE(_log_send_sem);
+
+    if (_io_thread_started) {
+        return;
+    }
+
+    if (!hal.scheduler->thread_create(FUNCTOR_BIND_MEMBER(&AP_Logger::io_thread, void), "log_io", HAL_LOGGING_STACK_SIZE, AP_HAL::Scheduler::PRIORITY_IO, 0)) {
+        AP_HAL::panic("Failed to start Logger IO thread");
+    }
+
+    _io_thread_started = true;
+    return;
+}
+
 /* End of Write support */
 
 #undef FOR_EACH_BACKEND

libraries/AP_Logger/AP_Logger.h

@@ -498,6 +498,12 @@ private:
     // remember formats for replay
     void save_format_Replay(const void *pBuffer);
 
+    // io thread support
+    bool _io_thread_started;
+
+    void start_io_thread(void);
+    void io_thread();
+
     /* support for retrieving logs via mavlink: */
 
     enum class TransferActivity {

libraries/AP_Logger/AP_Logger_Backend.h

@@ -132,6 +132,8 @@ public:
     bool Write_Multiplier(const struct MultiplierStructure *s);
     bool Write_Format_Units(const struct LogStructure *structure);
 
+    virtual void io_timer(void) {}
+
 protected:
 
     AP_Logger &_front;

libraries/AP_Logger/AP_Logger_Block.cpp

@@ -57,8 +57,6 @@ void AP_Logger_Block::Init(void)
     }
 
     WITH_SEMAPHORE(sem);
-
-    hal.scheduler->register_io_process(FUNCTOR_BIND_MEMBER(&AP_Logger_Block::io_timer, void));
 }
 
 uint32_t AP_Logger_Block::bufferspace_available()

libraries/AP_Logger/AP_Logger_Block.h

@@ -31,6 +31,7 @@ public:
     void stop_logging_async(void) override;
     bool logging_failed() const override;
     bool logging_started(void) const override { return log_write_started; }
+    void io_timer(void) override;
 
 protected:
     /* Write a block of data at current offset */
@@ -159,6 +160,5 @@ private:
 
     // callback on IO thread
     bool io_thread_alive() const;
-    void io_timer(void);
     void write_log_page();
 };

libraries/AP_Logger/AP_Logger_File.cpp

@@ -99,7 +99,6 @@ void AP_Logger_File::Init()
     hal.console->printf("AP_Logger_File: buffer size=%u\n", (unsigned)bufsize);
 
     _initialised = true;
-    hal.scheduler->register_io_process(FUNCTOR_BIND_MEMBER(&AP_Logger_File::_io_timer, void));
 
     const char* custom_dir = hal.util->get_custom_log_directory();
     if (custom_dir != nullptr){
@@ -873,7 +872,7 @@ void AP_Logger_File::flush(void)
         if (tnow > 2001) { // avoid resetting _last_write_time to 0
             _last_write_time = tnow - 2001;
         }
-        _io_timer();
+        io_timer();
     }
     if (write_fd_semaphore.take(1)) {
         if (_write_fd != -1) {
@@ -891,7 +890,7 @@ void AP_Logger_File::flush(void)
 #endif // APM_BUILD_TYPE(APM_BUILD_Replay) || APM_BUILD_TYPE(APM_BUILD_UNKNOWN)
 #endif
 
-void AP_Logger_File::_io_timer(void)
+void AP_Logger_File::io_timer(void)
 {
     uint32_t tnow = AP_HAL::millis();
     _io_timer_heartbeat = tnow;

libraries/AP_Logger/AP_Logger_File.h

@@ -54,6 +54,7 @@ public:
     bool logging_failed() const override;
 
     bool logging_started(void) const override { return _write_fd != -1; }
+    void io_timer(void) override;
 
 protected:
 
@@ -109,8 +110,6 @@ private:
 
     void stop_logging(void) override;
 
-    void _io_timer(void);
-
     uint32_t last_messagewrite_message_sent;
 
     // free-space checks; filling up SD cards under NuttX leads to