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feat(midi2): opt-in app responder for UMP Stream #3739

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sauloverissimo wants to merge 1 commit into from
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feat(midi2): opt-in app responder for UMP Stream #3739

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16 changes: 16 additions & 0 deletions src/class/midi/midi2_device.c
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Original file line number Diff line number Diff line change
Expand Up @@ -270,6 +270,7 @@ static uint32_t _tx_ump_write(midi2d_interface_t* p_midi, const uint32_t* words,
//--------------------------------------------------------------------+
// Protocol Negotiation
//--------------------------------------------------------------------+
#if !CFG_TUD_MIDI2_USER_RESPONDER
static void _nego_send_ump(midi2d_interface_t* p_midi, const uint32_t* words, uint8_t count) {
if (!_tx_opened(p_midi)) return;
if (tu_fifo_remaining(&p_midi->ep_stream.tx.ff) < (uint32_t) count * 4) return;
Expand Down Expand Up @@ -383,8 +384,16 @@ static void _nego_handle_stream_msg(midi2d_interface_t* p_midi, const uint32_t*
break;
}
}
#endif // !CFG_TUD_MIDI2_USER_RESPONDER

static void _nego_process_rx(midi2d_interface_t* p_midi) {
#if CFG_TUD_MIDI2_USER_RESPONDER
// User responder owns UMP Stream discovery: MT 0xF messages stay in the
// RX FIFO and surface through tud_midi2_n_ump_read so the application can
// answer Endpoint / Function Block discovery itself. The app must drain
// them (e.g. in tud_midi2_rx_cb) to avoid RX FIFO backpressure.
(void)p_midi;
Comment on lines +390 to +395

@chatgpt-codex-connector chatgpt-codex-connector Bot Jun 27, 2026

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P2 Badge Preserve negotiation state in user responder mode

With CFG_TUD_MIDI2_USER_RESPONDER=1, this branch returns before the only code path that handles STREAM_CONFIG_REQUEST; since there is also no public setter for p_midi->protocol or p_midi->negotiated, an application that accepts a host's MIDI 1.0 Config Request and sends its own Config Notify will still see tud_midi2_n_protocol() report the reset default MIDI2 and tud_midi2_n_negotiated() stay false. Please either keep parsing config requests for state or provide a way for the user responder to update these getters.

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#else
tu_edpt_stream_t* ep_rx = &p_midi->ep_stream.rx;
uint8_t word_bytes[4];

Expand All @@ -402,6 +411,7 @@ static void _nego_process_rx(midi2d_interface_t* p_midi) {
tu_edpt_stream_read(ep_rx, buf, pkt_bytes);

@HiFiPhile HiFiPhile Jun 27, 2026

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I'm thinking about adding a weak callback here, with the return value we can differentiate between Handled, Negotiated to V1 , Negotiated to V2 , etc.

Maybe the user only want to override a one specific response instead of implement full negotiation in app.

@sauloverissimo sauloverissimo Jun 27, 2026

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Hi @HiFiPhile! Are you thinking of a per-message hook at the stream dispatch, where the return value decides fallthrough vs handled? So the app could intercept just FB Discovery, say, and let the built-in responder take the rest.

@HiFiPhile HiFiPhile Jun 27, 2026

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Yes exactely.

_nego_handle_stream_msg(p_midi, buf);
}
#endif
}

//--------------------------------------------------------------------+
Expand Down Expand Up @@ -510,6 +520,12 @@ uint8_t tud_midi2_n_protocol(uint8_t itf) {
return _midi2d_itf[itf].protocol;
}

void tud_midi2_n_set_protocol(uint8_t itf, uint8_t protocol) {
TU_VERIFY(itf < CFG_TUD_MIDI2, );
_midi2d_itf[itf].protocol = protocol;
_midi2d_itf[itf].negotiated = true;
}

//--------------------------------------------------------------------+
// USBD Driver API
//--------------------------------------------------------------------+
Expand Down
18 changes: 18 additions & 0 deletions src/class/midi/midi2_device.h
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Expand Up @@ -86,6 +86,16 @@ extern "C" {
#define CFG_TUD_MIDI2_BLOCK_STRIDX 0
#endif

// When set to 1, the built-in UMP Stream responder is disabled and MT 0xF
// (Stream) messages are left in the RX FIFO for the application to handle
// (Endpoint / Function Block discovery, Stream Configuration). The app must
// drain them (e.g. in tud_midi2_rx_cb) to avoid RX FIFO backpressure, and
// call tud_midi2_n_set_protocol() after accepting a Stream Configuration
// Request to keep tud_midi2_n_protocol / tud_midi2_n_negotiated accurate.
#ifndef CFG_TUD_MIDI2_USER_RESPONDER
#define CFG_TUD_MIDI2_USER_RESPONDER 0
#endif

//--------------------------------------------------------------------+
// MIDI Protocol Values (returned by tud_midi2_n_protocol)
//--------------------------------------------------------------------+
Expand Down Expand Up @@ -119,6 +129,10 @@ 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);

// Record the negotiated protocol when the application owns UMP Stream
// negotiation (CFG_TUD_MIDI2_USER_RESPONDER). Marks the endpoint negotiated.
void tud_midi2_n_set_protocol(uint8_t itf, uint8_t protocol);

// Read up to max_words UMP words from the RX FIFO. Returns the number of
// words actually read (0 if FIFO is empty).
//
Expand Down Expand Up @@ -156,6 +170,10 @@ TU_ATTR_ALWAYS_INLINE static inline uint8_t tud_midi2_protocol(void) {
return tud_midi2_n_protocol(0);
}

TU_ATTR_ALWAYS_INLINE static inline void tud_midi2_set_protocol(uint8_t protocol) {
tud_midi2_n_set_protocol(0, protocol);
}

TU_ATTR_ALWAYS_INLINE static inline uint32_t
tud_midi2_ump_read(uint32_t* words, uint32_t max_words) {
return tud_midi2_n_ump_read(0, words, max_words);
Expand Down
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