midi2: drain pattern for RX FIFO

Default RX/TX buffers to EPSIZE for both device and host. Document
drain-in-loop on ump_read; example device callback drains until
empty.

examples/device/midi2_device/src/main.c

@@ -529,7 +529,13 @@ void send_initial_setup(void);
 //--------------------------------------------------------------------+
 
 void tud_midi2_rx_cb(uint8_t itf) {
-  (void)itf;
+  // Drain the RX FIFO in a loop until empty. Leaving words in the FIFO
+  // across callbacks can prevent subsequent bulk OUT transfers from landing.
+  uint32_t words[8];
+  uint32_t n;
+  while ((n = tud_midi2_n_ump_read(itf, words, TU_ARRAY_SIZE(words))) > 0) {
+    (void) n;
+  }
 }
 
 // Reset playback state and re-send setup when host switches alt setting or

src/class/midi/midi2_device.h

@@ -57,11 +57,11 @@ extern "C" {
 #endif
 
 #ifndef CFG_TUD_MIDI2_TX_BUFSIZE
-  #define CFG_TUD_MIDI2_TX_BUFSIZE  (4 * CFG_TUD_MIDI2_TX_EPSIZE)
+  #define CFG_TUD_MIDI2_TX_BUFSIZE  CFG_TUD_MIDI2_TX_EPSIZE
 #endif
 
 #ifndef CFG_TUD_MIDI2_RX_BUFSIZE
-  #define CFG_TUD_MIDI2_RX_BUFSIZE  (4 * CFG_TUD_MIDI2_RX_EPSIZE)
+  #define CFG_TUD_MIDI2_RX_BUFSIZE  CFG_TUD_MIDI2_RX_EPSIZE
 #endif
 
 #ifndef CFG_TUD_MIDI2_NUM_GROUPS
@@ -119,6 +119,14 @@ uint8_t  tud_midi2_n_alt_setting(uint8_t itf);
 bool     tud_midi2_n_negotiated(uint8_t itf);
 uint8_t  tud_midi2_n_protocol(uint8_t itf);
 
+// Read up to max_words UMP words from the RX FIFO. Returns the number of
+// words actually read (0 if FIFO is empty).
+//
+// NOTE: this function returns when max_words is reached or when the FIFO is
+// empty, whichever comes first. Applications should invoke it in a loop
+// until it returns 0 to guarantee the RX FIFO is fully drained per
+// tud_midi2_rx_cb callback. Leaving words in the FIFO across callbacks can
+// prevent subsequent bulk OUT transfers from landing.
 uint32_t tud_midi2_n_ump_read(uint8_t itf, uint32_t* words, uint32_t max_words);
 uint32_t tud_midi2_n_ump_write(uint8_t itf, const uint32_t* words, uint32_t count);
 

src/class/midi/midi2_host.h

@@ -77,6 +77,14 @@ uint8_t  tuh_midi2_get_cable_count(uint8_t idx);
 // Application API - I/O
 //--------------------------------------------------------------------+
 
+// Read up to max_words UMP words from the RX FIFO. Returns the number of
+// words actually read (0 if FIFO is empty).
+//
+// NOTE: this function returns when max_words is reached or when the FIFO is
+// empty, whichever comes first. Applications should invoke it in a loop
+// until it returns 0 to guarantee the RX FIFO is fully drained per
+// tuh_midi2_rx_cb callback. Leaving words in the FIFO across callbacks can
+// prevent subsequent bulk IN transfers from landing.
 uint32_t tuh_midi2_ump_read(uint8_t idx, uint32_t* words, uint32_t max_words);
 uint32_t tuh_midi2_ump_write(uint8_t idx, const uint32_t* words, uint32_t count);
 uint32_t tuh_midi2_write_flush(uint8_t idx);

src/tusb_option.h

@@ -824,11 +824,11 @@
 #endif
 
 #ifndef CFG_TUH_MIDI2_RX_BUFSIZE
-  #define CFG_TUH_MIDI2_RX_BUFSIZE (4 * TUH_EPSIZE_BULK_MAX)
+  #define CFG_TUH_MIDI2_RX_BUFSIZE TUH_EPSIZE_BULK_MAX
 #endif
 
 #ifndef CFG_TUH_MIDI2_TX_BUFSIZE
-  #define CFG_TUH_MIDI2_TX_BUFSIZE (4 * TUH_EPSIZE_BULK_MAX)
+  #define CFG_TUH_MIDI2_TX_BUFSIZE TUH_EPSIZE_BULK_MAX
 #endif
 
 #ifndef CFG_TUH_MIDI2_LOG_LEVEL