HAL_ChibiOS: fixed stdout in early startup bug

this caused a failure to boot on some boards if they tried to print
messages in early startup code before hal was initialised

thanks to @Shadowru for reporting the issue

libraries/AP_HAL_ChibiOS/HAL_ChibiOS_Class.cpp

@@ -279,8 +279,8 @@ void HAL_ChibiOS::run(int argc, char * const argv[], Callbacks* callbacks) const
      *   RTOS is active.
      */
 
-#ifdef HAL_USB_PRODUCT_ID
+#if HAL_USE_SERIAL_USB == TRUE
-  setup_usb_strings();
+    usb_initialise();
 #endif
 
 #ifdef HAL_STDOUT_SERIAL

libraries/AP_HAL_ChibiOS/UARTDriver.cpp

@@ -1446,4 +1446,35 @@ uint8_t UARTDriver::get_options(void) const
     return _last_options;
 }
 
+#if HAL_USE_SERIAL_USB == TRUE
+/*
+  initialise the USB bus, called from both UARTDriver and stdio for startup debug
+  This can be called before the hal is initialised so must not call any hal functions
+ */
+void usb_initialise(void)
+{
+    static bool initialised;
+    if (initialised) {
+        return;
+    }
+    initialised = true;
+    setup_usb_strings();
+    sduObjectInit(&SDU1);
+    sduStart(&SDU1, &serusbcfg1);
+#if HAL_HAVE_DUAL_USB_CDC
+    sduObjectInit(&SDU2);
+    sduStart(&SDU2, &serusbcfg2);
+#endif
+    /*
+     * Activates the USB driver and then the USB bus pull-up on D+.
+     * Note, a delay is inserted in order to not have to disconnect the cable
+     * after a reset.
+     */
+    usbDisconnectBus(serusbcfg1.usbp);
+    chThdSleep(chTimeUS2I(1500));
+    usbStart(serusbcfg1.usbp, &usbcfg);
+    usbConnectBus(serusbcfg1.usbp);
+}
+#endif
+
 #endif //CONFIG_HAL_BOARD == HAL_BOARD_CHIBIOS

libraries/AP_HAL_ChibiOS/UARTDriver.h

@@ -238,3 +238,6 @@ private:
     void thread_init();
     static void uart_thread(void *);
 };
+
+// access to usb init for stdio.cpp
+void usb_initialise(void);

libraries/AP_HAL_ChibiOS/stdio.cpp

@@ -31,6 +31,7 @@
 #include <AP_HAL/AP_HAL.h>
 #if HAL_USE_SERIAL_USB == TRUE
 #include <AP_HAL_ChibiOS/hwdef/common/usbcfg.h>
+#include "UARTDriver.h"
 #endif
 
 extern const AP_HAL::HAL& hal;
@@ -85,6 +86,7 @@ int __wrap_vprintf(const char *fmt, va_list arg)
 #ifdef HAL_STDOUT_SERIAL
   return chvprintf((BaseSequentialStream*)&HAL_STDOUT_SERIAL, fmt, arg);
 #elif HAL_USE_SERIAL_USB == TRUE
+  usb_initialise();
   return chvprintf((BaseSequentialStream*)&SDU1, fmt, arg);
 #else
   (void)arg;