Merge pull request #1235 from vmilea/feature/feedback_format

Support disabling feedback format correction #1234

src/class/audio/audio_device.c

@@ -2247,24 +2247,28 @@ static void audiod_parse_for_AS_params(audiod_function_t* audio, uint8_t const *
 
 #if CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
 
-// Input value feedback has to be in 16.16 format - the format will be converted according to speed settings automatically
 bool tud_audio_n_fb_set(uint8_t func_id, uint32_t feedback)
 {
   TU_VERIFY(func_id < CFG_TUD_AUDIO && _audiod_fct[func_id].p_desc != NULL);
 
   // Format the feedback value
-#if !TUD_OPT_HIGH_SPEED
-  uint8_t * fb = (uint8_t *) &_audiod_fct[func_id].fb_val;
-
-  // For FS format is 10.14
-  *(fb++) = (feedback >> 2) & 0xFF;
-  *(fb++) = (feedback >> 10) & 0xFF;
-  *(fb++) = (feedback >> 18) & 0xFF;
-  // 4th byte is needed to work correctly with MS Windows
-  *fb = 0;
+#if CFG_TUD_AUDIO_ENABLE_FEEDBACK_FORMAT_CORRECTION
+  if ( TUSB_SPEED_FULL == tud_speed_get() )
+  {
+    uint8_t * fb = (uint8_t *) &_audiod_fct[func_id].fb_val;
+
+    // For FS format is 10.14
+    *(fb++) = (feedback >> 2) & 0xFF;
+    *(fb++) = (feedback >> 10) & 0xFF;
+    *(fb++) = (feedback >> 18) & 0xFF;
+    // 4th byte is needed to work correctly with MS Windows
+    *fb = 0;
+  }else
 #else
-  // For HS format is 16.16 as originally demanded
-  _audiod_fct[func_id].fb_val = feedback;
+  {
+    // Send value as-is, caller will choose the appropriate format
+    _audiod_fct[func_id].fb_val = feedback;
+  }
 #endif
 
   // Schedule a transmit with the new value if EP is not busy - this triggers repetitive scheduling of the feedback value

src/class/audio/audio_device.h

@@ -186,6 +186,11 @@
 #define CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP                    0                             // Feedback - 0 or 1
 #endif
 
+// Enable/disable conversion from 16.16 to 10.14 format on full-speed devices. See tud_audio_n_fb_set().
+#ifndef CFG_TUD_AUDIO_ENABLE_FEEDBACK_FORMAT_CORRECTION
+#define CFG_TUD_AUDIO_ENABLE_FEEDBACK_FORMAT_CORRECTION     0                             // 0 or 1
+#endif
+
 // Audio interrupt control EP size - disabled if 0
 #ifndef CFG_TUD_AUDIO_INT_CTR_EPSIZE_IN
 #define CFG_TUD_AUDIO_INT_CTR_EPSIZE_IN                     0                             // Audio interrupt control - if required - 6 Bytes according to UAC 2 specification (p. 74)
@@ -454,10 +459,15 @@ TU_ATTR_WEAK bool tud_audio_rx_done_post_read_cb(uint8_t rhport, uint16_t n_byte
 
 #if CFG_TUD_AUDIO_ENABLE_EP_OUT && CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
 TU_ATTR_WEAK bool tud_audio_fb_done_cb(uint8_t rhport);
-// User code should call this function with feedback value in 16.16 format for FS and HS.
-// Value will be corrected for FS to 10.14 format automatically.
-// (see Universal Serial Bus Specification Revision 2.0 5.12.4.2).
-// Feedback value will be sent at FB endpoint interval till it's changed.
+
+// This function is used to provide data rate feedback from an asynchronous sink. Feedback value will be sent at FB endpoint interval till it's changed.
+//
+// The feedback format is specified to be 16.16 for HS and 10.14 for FS devices (see Universal Serial Bus Specification Revision 2.0 5.12.4.2). By default,
+// the choice of format is left to the caller and feedback argument is sent as-is. If CFG_TUD_AUDIO_ENABLE_FEEDBACK_FORMAT_CORRECTION is set, then tinyusb
+// expects 16.16 format and handles the conversion to 10.14 on FS.
+//
+// Note that due to a bug in its USB Audio 2.0 driver, Windows currently requires 16.16 format for _all_ USB 2.0 devices. On Linux and macOS it seems the 
+// driver can work with either format. So a good compromise is to keep format correction disabled and stick to 16.16 format.
 bool tud_audio_n_fb_set(uint8_t func_id, uint32_t feedback);
 static inline bool tud_audio_fb_set(uint32_t feedback);
 #endif