HAL_ChibiOS: don't clear buffers if no baudrate change

libraries/AP_HAL_ChibiOS/UARTDriver.cpp

@@ -155,13 +155,19 @@ void UARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
         _initialised = false;
         _readbuf.set_size(rxS);
     }
-    if (hal.console != this) { // don't clear USB buffers (allows early startup messages to escape)
-        _readbuf.clear();
-    }
 
+    bool clear_buffers = false;
     if (b != 0) {
+        // clear buffers on baudrate change, but not on the console (which is usually USB)
+        if (_baudrate != b && hal.console != this) {
+            clear_buffers = true;
+        }
         _baudrate = b;
     }
+    
+    if (clear_buffers) {
+        _readbuf.clear();
+    }
 
     if (rx_bounce_buf == nullptr) {
         rx_bounce_buf = (uint8_t *)hal.util->malloc_type(RX_BOUNCE_BUFSIZE, AP_HAL::Util::MEM_DMA_SAFE);
@@ -182,7 +188,8 @@ void UARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
         _initialised = false;
         _writebuf.set_size(txS);
     }
-    if (hal.console != this) { // don't clear USB buffers (allows early startup messages to escape)
+
+    if (clear_buffers) {
         _writebuf.clear();
     }