add more doxygen docs

start to use TUSB_Error_t

tinyusb/common/errors.h

@@ -42,23 +42,29 @@
  */
 
 /** \ingroup Group_Common
- *
+ *  \defgroup Group_Error tinyUSB Error Codes
  *  @{
  */
 
 #ifndef _TUSB_ERRORS_H_
 #define _TUSB_ERRORS_H_
 
-enum TUSB_ERROR {
+/** \enum TUSB_Error
+ *  \brief Error Code returned
+ */
+
+typedef enum {
 #   define ERROR_ENUM(x) x,
 #   include "errors_def"
 #   undef ERROR_ENUM
-};
+  ERROR_COUNT
+}TUSB_Error_t;
 
 #ifdef __cplusplus
  extern "C" {
 #endif
 
+/// Enum to String for debugging purposes. Only available if \ref CFG_TUSB_DEBUG_LEVEL > 0
 extern char const* const TUSB_ErrorStr[];
 
 #ifdef __cplusplus
@@ -66,3 +72,5 @@ extern char const* const TUSB_ErrorStr[];
 #endif
 
 #endif /* _TUSB_ERRORS_H_ */
+
+ /**  @{ */