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Merge pull request #54309 from ibrahn/alsa-midi-fix
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Fix MIDI input with ALSA
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@akien-mga
akien-mga committed Oct 31, 2022
2 parents dcd86f9 + 8157517 commit d6aa307
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Showing 2 changed files with 154 additions and 68 deletions.
184 changes: 117 additions & 67 deletions drivers/alsamidi/midi_driver_alsamidi.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -37,85 +37,135 @@

#include <errno.h>

static int get_message_size(uint8_t message) {
switch (message & 0xF0) {
case 0x80: // note off
case 0x90: // note on
case 0xA0: // aftertouch
case 0xB0: // continuous controller
case 0xE0: // pitch bend
case 0xF2: // song position pointer
return 3;

case 0xC0: // patch change
case 0xD0: // channel pressure
case 0xF1: // time code quarter frame
case 0xF3: // song select
MIDIDriverALSAMidi::MessageCategory MIDIDriverALSAMidi::msg_category(uint8_t msg_part) {
if (msg_part >= 0xf8) {
return MessageCategory::RealTime;
} else if (msg_part >= 0xf0) {
// System Exclusive begin/end are specified as System Common Category messages,
// but we separate them here and give them their own categories as their
// behaviour is significantly different.
if (msg_part == 0xf0) {
return MessageCategory::SysExBegin;
} else if (msg_part == 0xf7) {
return MessageCategory::SysExEnd;
}
return MessageCategory::SystemCommon;
} else if (msg_part >= 0x80) {
return MessageCategory::Voice;
}
return MessageCategory::Data;
}

size_t MIDIDriverALSAMidi::msg_expected_data(uint8_t status_byte) {
if (msg_category(status_byte) == MessageCategory::Voice) {
// Voice messages have a channel number in the status byte, mask it out.
status_byte &= 0xf0;
}

switch (status_byte) {
case 0x80: // Note Off
case 0x90: // Note On
case 0xA0: // Polyphonic Key Pressure (Aftertouch)
case 0xB0: // Control Change (CC)
case 0xE0: // Pitch Bend Change
case 0xF2: // Song Position Pointer
return 2;

case 0xF0: // SysEx start
case 0xF4: // reserved
case 0xF5: // reserved
case 0xF6: // tune request
case 0xF7: // SysEx end
case 0xF8: // timing clock
case 0xF9: // reserved
case 0xFA: // start
case 0xFB: // continue
case 0xFC: // stop
case 0xFD: // reserved
case 0xFE: // active sensing
case 0xFF: // reset
case 0xC0: // Program Change
case 0xD0: // Channel Pressure (Aftertouch)
case 0xF1: // MIDI Time Code Quarter Frame
case 0xF3: // Song Select
return 1;
}

return 256;
return 0;
}

void MIDIDriverALSAMidi::InputConnection::parse_byte(uint8_t byte, MIDIDriverALSAMidi &driver,
uint64_t timestamp) {
switch (msg_category(byte)) {
case MessageCategory::RealTime:
// Real-Time messages are single byte messages that can
// occur at any point.
// We pass them straight through.
driver.receive_input_packet(timestamp, &byte, 1);
break;

case MessageCategory::Data:
// We don't currently forward System Exclusive messages so skip their data.
// Collect any expected data for other message types.
if (!skipping_sys_ex && expected_data > received_data) {
buffer[received_data + 1] = byte;
received_data++;

// Forward a complete message and reset relevant state.
if (received_data == expected_data) {
driver.receive_input_packet(timestamp, buffer, received_data + 1);
received_data = 0;

if (msg_category(buffer[0]) != MessageCategory::Voice) {
// Voice Category messages can be sent with "running status".
// This means they don't resend the status byte until it changes.
// For other categories, we reset expected data, to require a new status byte.
expected_data = 0;
}
}
}
break;

case MessageCategory::SysExBegin:
buffer[0] = byte;
skipping_sys_ex = true;
break;

case MessageCategory::SysExEnd:
expected_data = 0;
skipping_sys_ex = false;
break;

case MessageCategory::Voice:
case MessageCategory::SystemCommon:
buffer[0] = byte;
received_data = 0;
expected_data = msg_expected_data(byte);
skipping_sys_ex = false;
if (expected_data == 0) {
driver.receive_input_packet(timestamp, &byte, 1);
}
break;
}
}

int MIDIDriverALSAMidi::InputConnection::read_in(MIDIDriverALSAMidi &driver, uint64_t timestamp) {
int ret;
do {
uint8_t byte = 0;
ret = snd_rawmidi_read(rawmidi_ptr, &byte, 1);

if (ret < 0) {
if (ret != -EAGAIN) {
ERR_PRINT("snd_rawmidi_read error: " + String(snd_strerror(ret)));
}
} else {
parse_byte(byte, driver, timestamp);
}
} while (ret > 0);

return ret;
}

void MIDIDriverALSAMidi::thread_func(void *p_udata) {
MIDIDriverALSAMidi *md = static_cast<MIDIDriverALSAMidi *>(p_udata);
uint64_t timestamp = 0;
uint8_t buffer[256];
int expected_size = 255;
int bytes = 0;

while (!md->exit_thread.is_set()) {
int ret;

md->lock();

for (int i = 0; i < md->connected_inputs.size(); i++) {
snd_rawmidi_t *midi_in = md->connected_inputs[i];
do {
uint8_t byte = 0;
ret = snd_rawmidi_read(midi_in, &byte, 1);
if (ret < 0) {
if (ret != -EAGAIN) {
ERR_PRINT("snd_rawmidi_read error: " + String(snd_strerror(ret)));
}
} else {
if (byte & 0x80) {
// Flush previous packet if there is any
if (bytes) {
md->receive_input_packet(timestamp, buffer, bytes);
bytes = 0;
}
expected_size = get_message_size(byte);
// After a SysEx start, all bytes are data until a SysEx end, so
// we're going to end the command at the SES, and let the common
// driver ignore the following data bytes.
}
InputConnection *connections = md->connected_inputs.ptrw();
size_t connection_count = md->connected_inputs.size();

if (bytes < 256) {
buffer[bytes++] = byte;
// If we know the size of the current packet receive it if it reached the expected size
if (bytes >= expected_size) {
md->receive_input_packet(timestamp, buffer, bytes);
bytes = 0;
}
}
}
} while (ret > 0);
for (size_t i = 0; i < connection_count; i++) {
connections[i].read_in(*md, timestamp);
}

md->unlock();
Expand All @@ -139,7 +189,7 @@ Error MIDIDriverALSAMidi::open() {
snd_rawmidi_t *midi_in;
int ret = snd_rawmidi_open(&midi_in, nullptr, name, SND_RAWMIDI_NONBLOCK);
if (ret >= 0) {
connected_inputs.insert(i++, midi_in);
connected_inputs.insert(i++, InputConnection(midi_in));
}
}

Expand All @@ -160,7 +210,7 @@ void MIDIDriverALSAMidi::close() {
thread.wait_to_finish();

for (int i = 0; i < connected_inputs.size(); i++) {
snd_rawmidi_t *midi_in = connected_inputs[i];
snd_rawmidi_t *midi_in = connected_inputs[i].rawmidi_ptr;
snd_rawmidi_close(midi_in);
}
connected_inputs.clear();
Expand All @@ -179,7 +229,7 @@ PackedStringArray MIDIDriverALSAMidi::get_connected_inputs() {

lock();
for (int i = 0; i < connected_inputs.size(); i++) {
snd_rawmidi_t *midi_in = connected_inputs[i];
snd_rawmidi_t *midi_in = connected_inputs[i].rawmidi_ptr;
snd_rawmidi_info_t *info;

snd_rawmidi_info_malloc(&info);
Expand Down
38 changes: 37 additions & 1 deletion drivers/alsamidi/midi_driver_alsamidi.h
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Original file line number Diff line number Diff line change
Expand Up @@ -46,12 +46,48 @@ class MIDIDriverALSAMidi : public MIDIDriver {
Thread thread;
Mutex mutex;

Vector<snd_rawmidi_t *> connected_inputs;
class InputConnection {
public:
InputConnection() = default;
InputConnection(snd_rawmidi_t *midi_in) :
rawmidi_ptr{ midi_in } {}

// Read in and parse available data, forwarding any complete messages through the driver.
int read_in(MIDIDriverALSAMidi &driver, uint64_t timestamp);

snd_rawmidi_t *rawmidi_ptr = nullptr;

private:
static const size_t MSG_BUFFER_SIZE = 3;
uint8_t buffer[MSG_BUFFER_SIZE] = { 0 };
size_t expected_data = 0;
size_t received_data = 0;
bool skipping_sys_ex = false;
void parse_byte(uint8_t byte, MIDIDriverALSAMidi &driver, uint64_t timestamp);
};

Vector<InputConnection> connected_inputs;

SafeFlag exit_thread;

static void thread_func(void *p_udata);

enum class MessageCategory {
Data,
Voice,
SysExBegin,
SystemCommon, // excluding System Exclusive Begin/End
SysExEnd,
RealTime,
};

// If the passed byte is a status byte, return the associated message category,
// else return MessageCategory::Data.
static MessageCategory msg_category(uint8_t msg_part);

// Return the number of data bytes expected for the provided status byte.
static size_t msg_expected_data(uint8_t status_byte);

void lock() const;
void unlock() const;

Expand Down

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