Teensy 3.6 USB midi sysex errors

rvh · Aug 18, 2022

This is cross posted from a thread in the general discussion about a Teensy 4.1 issue: https://forum.pjrc.com/threads/70288-usbMIDI-transmission-error?p=311329#post311329

But for my purposes it belongs here as I am at a loss regarding how to solve this for Teensy 3.6. I am trying to transfer a bank of patches from my T3.6 synth using usb sysex, and monitoring results using midi Ox. It seems I can transfer a single patch ok, but sending many causes problems. So I coded a simple illustration of my problem with dummy data.

Below is that code, using a button press on pin 2 to start a dump. It should show 50000 bytes transferred, and sometimes it does (especially the first one or two times it's run it seems). But as often as not, there are some bytes missing, and the count is less than 50000. And changing the buffer size, or delay values etc. doesn't seem to solve it. Please let me know if you have any ideas on what else I can try. Thanks!

Code:

#include <Arduino.h>  
#include <MIDI.h> 
MIDI_CREATE_INSTANCE(HardwareSerial, Serial1, MIDI ); 

void setup() {
  pinMode(2, INPUT_PULLUP);
  MIDI.begin(MIDI_CHANNEL_OMNI); // midi serial init 
}

void loop() {

  if(!digitalRead(2))
  {
   byte patchData[50] = {0};  
   patchData[0]=0xF0;                    
   patchData[49]=0xF7;    
  
   for(int P=0;P<50;P++)    
   {                     
     for(int i=0;i<20;i++)
     {  
        usbMIDI.sendSysEx( 50, patchData, true);        
        delay(10);                  
     }   
     delay(50);
   } 
  }   
}

p.s. I've tried multiple teensies and usb cables, and even dropped the clock speed all the way down to 24Mhz, all without seeing any difference in behavior.

rvh · Aug 18, 2022

I can confirm that if I send the sysex out of the Teensy using serial midi over a 5-pin DIN cable, rather than USB, everything works just fine. In that case I used an external device to translate the 5-pin din signal back to USB, and into midi Ox in the same way as before.

So the issue seems specific to the way the Teensy is sending USB sysex midi out, which was also the case in the other thread I mentioned re Teensy 4.1.

rvh · Aug 19, 2022

I received information from h4yn0nnym0u5e via the other thread about how to apply Rolfdegen's change to the library for Teensy 3.

In short, what is needed is to comment out line 957 of usb_dev.c:
#ifdef MIDI_INTERFACE
// usb_midi_flush_output();
#endif

and instead place the flush in your own code directly after any usbMIDI.sendSysEx() call. For the dummy example code above this amounts to:

Code:

#include <Arduino.h>  
#include <MIDI.h> 
MIDI_CREATE_INSTANCE(HardwareSerial, Serial1, MIDI ); 

void setup() {
  pinMode(2, INPUT_PULLUP);
  MIDI.begin(MIDI_CHANNEL_OMNI); // midi serial init 
}

void loop() {

  if(!digitalRead(2))
  {
   byte patchData[50] = {0};  
   patchData[0]=0xF0;                    
   patchData[49]=0xF7;    
  
   for(int P=0;P<50;P++)    
   {                     
     for(int i=0;i<20;i++)
     {  
        usbMIDI.sendSysEx( 50, patchData, true);     
        usb_midi_flush_output(); 
        delay(10);                  
     }   
     delay(50);
   } 
  }   
}

My sysex transfers are now completely reliable using this simple change. As I also mentioned in the other thread: Paul, if you see this, are you able to make use of these findings for both T3 & T4 to improve the library?

rvh · Aug 19, 2022

After more thorough testing, it seems this is not a good solution because some of my other midi USB functions misbehaved (badly) after making the change. It seems we need the change specifically for sysex transfers, but not other USB midi functions.

rvh · Aug 19, 2022

Here is the solution that works for me on T3.6. Rather than commenting out the midi_flush_output line as suggested before, add a variable at the top of the usb_midi.c that is used to notify the flush routine that a sysex write is in progress.

Then modify the two sysex write routines to set that flag while the routines are active. The routines are called usb_midi_send_sysex_buffer_has_term() and usb_midi_send_sysex_add_term_bytes(). After setting the flag back to 0 at the end of those routines, add a call to the flush routine usb_midi_flush_output() so you don't need to do this in your own program after each sysex buffer write.

Lastly, modify usb_midi_flush_output to check the flag is not set before continuing with any processing.

Here is my modified version of usb_midi.c for Teensy 3, but a simlar approach should work for T4. In the code, the lines that have been added have my initials (rvh) as a comment so you can see where I've made changes

Code:

/* Teensyduino Core Library
 * http://www.pjrc.com/teensy/
 * Copyright (c) 2017 PJRC.COM, LLC.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * 1. The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * 2. If the Software is incorporated into a build system that allows
 * selection among a list of target devices, then similar target
 * devices manufactured by PJRC.COM must be included in the list of
 * target devices and selectable in the same manner.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "usb_dev.h"
#include "usb_midi.h"
#include "core_pins.h" // for yield()
#include "HardwareSerial.h"

#ifdef MIDI_INTERFACE // defined by usb_dev.h -> usb_desc.h
#if F_CPU >= 20000000

uint8_t usb_midi_msg_cable;
uint8_t usb_midi_msg_channel;
uint8_t usb_midi_msg_type;
uint8_t usb_midi_msg_data1;
uint8_t usb_midi_msg_data2;
// TODO: separate sysex buffers for each cable...
uint8_t usb_midi_msg_sysex[USB_MIDI_SYSEX_MAX];
uint16_t usb_midi_msg_sysex_len;
void (*usb_midi_handleNoteOff)(uint8_t ch, uint8_t note, uint8_t vel) = NULL;
void (*usb_midi_handleNoteOn)(uint8_t ch, uint8_t note, uint8_t vel) = NULL;
void (*usb_midi_handleVelocityChange)(uint8_t ch, uint8_t note, uint8_t vel) = NULL;
void (*usb_midi_handleControlChange)(uint8_t ch, uint8_t control, uint8_t value) = NULL;
void (*usb_midi_handleProgramChange)(uint8_t ch, uint8_t program) = NULL;
void (*usb_midi_handleAfterTouch)(uint8_t ch, uint8_t pressure) = NULL;
void (*usb_midi_handlePitchChange)(uint8_t ch, int pitch) = NULL;
void (*usb_midi_handleSysExPartial)(const uint8_t *data, uint16_t length, uint8_t complete) = NULL;
void (*usb_midi_handleSysExComplete)(uint8_t *data, unsigned int size) = NULL;
void (*usb_midi_handleTimeCodeQuarterFrame)(uint8_t data) = NULL;
void (*usb_midi_handleSongPosition)(uint16_t beats) = NULL;
void (*usb_midi_handleSongSelect)(uint8_t songnumber) = NULL;
void (*usb_midi_handleTuneRequest)(void) = NULL;
void (*usb_midi_handleClock)(void) = NULL;
void (*usb_midi_handleStart)(void) = NULL;
void (*usb_midi_handleContinue)(void) = NULL;
void (*usb_midi_handleStop)(void) = NULL;
void (*usb_midi_handleActiveSensing)(void) = NULL;
void (*usb_midi_handleSystemReset)(void) = NULL;
void (*usb_midi_handleRealTimeSystem)(uint8_t rtb) = NULL;


// Maximum number of transmit packets to queue so we don't starve other endpoints for memory
#define TX_PACKET_LIMIT 6
static usb_packet_t *rx_packet=NULL;
static usb_packet_t *tx_packet=NULL;
static uint8_t transmit_previous_timeout=0;
static uint8_t tx_noautoflush=0;

static uint8_t SysExInProgress = 0;  //  rvh

// When the PC isn't listening, how long do we wait before discarding data?
#define TX_TIMEOUT_MSEC 40
#if F_CPU == 256000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 1706)
#elif F_CPU == 240000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 1600)
#elif F_CPU == 216000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 1440)
#elif F_CPU == 192000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 1280)
#elif F_CPU == 180000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 1200)
#elif F_CPU == 168000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 1100)
#elif F_CPU == 144000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 932)
#elif F_CPU == 120000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 764)
#elif F_CPU == 96000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 596)
#elif F_CPU == 72000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 512)
#elif F_CPU == 48000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 428)
#elif F_CPU == 24000000
  #define TX_TIMEOUT (TX_TIMEOUT_MSEC * 262)
#endif


// This 32 bit input format is documented in the "Universal Serial Bus Device Class
// Definition for MIDI Devices" specification, version 1.0, Nov 1, 1999.  It can be
// downloaded from www.usb.org.  https://www.usb.org/sites/default/files/midi10.pdf
// If the USB-IF reorganizes their website and this link no longer works, Google
// search the name to find it.  This data format is shown on page 16 in Figure #8.
// Byte 0 (shown on the left hand side of Figure #8) is the least significant byte
// of this 32 bit input.
void usb_midi_write_packed(uint32_t n)
{
	uint32_t index, wait_count=0;

	tx_noautoflush = 1;
	if (!tx_packet) {
        	while (1) {
                	if (!usb_configuration) {
				//serial_print("error1\n");
                        	return;
                	}
                	if (usb_tx_packet_count(MIDI_TX_ENDPOINT) < TX_PACKET_LIMIT) {
                        	tx_packet = usb_malloc();
                        	if (tx_packet) break;
                	}
                	if (++wait_count > TX_TIMEOUT || transmit_previous_timeout) {
                        	transmit_previous_timeout = 1;
				//serial_print("error2\n");
                        	return;
                	}
                	yield();
        	}
	}
	transmit_previous_timeout = 0;
	index = tx_packet->index;
	((uint32_t *)(tx_packet->buf))[index++] = n;
	if (index < MIDI_TX_SIZE/4) {
		tx_packet->index = index;
	} else {
		tx_packet->len = MIDI_TX_SIZE;
		usb_tx(MIDI_TX_ENDPOINT, tx_packet);
		tx_packet = NULL;
	}
	tx_noautoflush = 0;
}

void usb_midi_send_sysex_buffer_has_term(const uint8_t *data, uint32_t length, uint8_t cable)
{
     SysExInProgress = 1;            // rvh
	
        cable = (cable & 0x0F) << 4;
        while (length > 3) {
                usb_midi_write_packed(0x04 | cable | (data[0] << 8) | (data[1] << 16) | (data[2] << 24));
                data += 3;
                length -= 3;
        }
        if (length == 3) {
                usb_midi_write_packed(0x07 | cable | (data[0] << 8) | (data[1] << 16) | (data[2] << 24));
        } else if (length == 2) {
                usb_midi_write_packed(0x06 | cable | (data[0] << 8) | (data[1] << 16));
        } else if (length == 1) {
                usb_midi_write_packed(0x05 | cable | (data[0] << 8));
        }

	SysExInProgress = 0;            // rvh
     usb_midi_flush_output();

}

void usb_midi_send_sysex_add_term_bytes(const uint8_t *data, uint32_t length, uint8_t cable)
{
	SysExInProgress = 1;            // rvh
	cable = (cable & 0x0F) << 4;

	if (length == 0) {
		usb_midi_write_packed(0x06 | cable | (0xF0 << 8) | (0xF7 << 16));
		return;
	} else if (length == 1) {
		usb_midi_write_packed(0x07 | cable | (0xF0 << 8) | (data[0] << 16) | (0xF7 << 24));
		return;
	} else {
		usb_midi_write_packed(0x04 | cable | (0xF0 << 8) | (data[0] << 16) | (data[1] << 24));
		data += 2;
		length -= 2;
	}
	while (length >= 3) {
		usb_midi_write_packed(0x04 | cable | (data[0] << 8) | (data[1] << 16) | (data[2] << 24));
		data += 3;
		length -= 3;
	}
	if (length == 2) {
		usb_midi_write_packed(0x07 | cable | (data[0] << 8) | (data[1] << 16) | (0xF7 << 24));
	} else if (length == 1) {
                usb_midi_write_packed(0x06 | cable | (data[0] << 8) | (0xF7 << 16));
	} else {
                usb_midi_write_packed(0x05 | cable | (0xF7 << 8));
	}
     SysExInProgress = 0;            // rvh
     usb_midi_flush_output();
}

void usb_midi_flush_output(void)
{
	if(SysExInProgress == 0)            // rvh
	if (tx_noautoflush == 0) {
		tx_noautoflush = 1;
		if (tx_packet && tx_packet->index > 0) {
			tx_packet->len = tx_packet->index * 4;
			usb_tx(MIDI_TX_ENDPOINT, tx_packet);
			tx_packet = NULL;
		}
		tx_noautoflush = 0;
	}
}

void static sysex_byte(uint8_t b)
{
	if (usb_midi_handleSysExPartial && usb_midi_msg_sysex_len >= USB_MIDI_SYSEX_MAX) {
		// when buffer is full, send another chunk to partial handler.
		(*usb_midi_handleSysExPartial)(usb_midi_msg_sysex, usb_midi_msg_sysex_len, 0);
		usb_midi_msg_sysex_len = 0;
	}
	if (usb_midi_msg_sysex_len < USB_MIDI_SYSEX_MAX) {
		usb_midi_msg_sysex[usb_midi_msg_sysex_len++] = b;
	}
}

uint32_t usb_midi_available(void)
{
	uint32_t index;

	if (!rx_packet) {
		if (!usb_configuration) return 0;
		rx_packet = usb_rx(MIDI_RX_ENDPOINT);
		if (!rx_packet) return 0;
		if (rx_packet->len == 0) {
			usb_free(rx_packet);
			rx_packet = NULL;
			return 0;
		}
	}
	index = rx_packet->index;
	return rx_packet->len - index;
}

uint32_t usb_midi_read_message(void)
{
	uint32_t n, index;

	if (!rx_packet) {
		if (!usb_configuration) return 0;
		rx_packet = usb_rx(MIDI_RX_ENDPOINT);
		if (!rx_packet) return 0;
		if (rx_packet->len == 0) {
			usb_free(rx_packet);
			rx_packet = NULL;
			return 0;
		}
	}
	index = rx_packet->index;
	n = ((uint32_t *)rx_packet->buf)[index/4];
	index += 4;
	if (index < rx_packet->len) {
		rx_packet->index = index;
	} else {
		usb_free(rx_packet);
		rx_packet = usb_rx(MIDI_RX_ENDPOINT);
	}
	return n;
}

int usb_midi_read(uint32_t channel)
{
	uint32_t n, index, ch, type1, type2, b1;

	if (!rx_packet) {
		if (!usb_configuration) return 0;
		rx_packet = usb_rx(MIDI_RX_ENDPOINT);
		if (!rx_packet) return 0;
		if (rx_packet->len == 0) {
			usb_free(rx_packet);
			rx_packet = NULL;
			return 0;
		}
	}
	index = rx_packet->index;
	n = ((uint32_t *)rx_packet->buf)[index/4];
	//serial_print("midi rx, n=");
	//serial_phex32(n);
	//serial_print("\n");
	index += 4;
	if (index < rx_packet->len) {
		rx_packet->index = index;
	} else {
		usb_free(rx_packet);
		rx_packet = usb_rx(MIDI_RX_ENDPOINT);
	}
	type1 = n & 15;
	type2 = (n >> 12) & 15;
	b1 = (n >> 8) & 0xFF;
	ch = (b1 & 15) + 1;
	usb_midi_msg_cable = (n >> 4) & 15;
	if (type1 >= 0x08 && type1 <= 0x0E) {
		if (channel && channel != ch) {
			// ignore other channels when user wants single channel read
			return 0;
		}
		if (type1 == 0x08 && type2 == 0x08) {
			usb_midi_msg_type = 0x80;		// 0x80 = usbMIDI.NoteOff
			if (usb_midi_handleNoteOff)
				(*usb_midi_handleNoteOff)(ch, (n >> 16), (n >> 24));
		} else
		if (type1 == 0x09 && type2 == 0x09) {
			if ((n >> 24) > 0) {
				usb_midi_msg_type = 0x90;	// 0x90 = usbMIDI.NoteOn
				if (usb_midi_handleNoteOn)
					(*usb_midi_handleNoteOn)(ch, (n >> 16), (n >> 24));
			} else {
				usb_midi_msg_type = 0x80;	// 0x80 = usbMIDI.NoteOff
				if (usb_midi_handleNoteOff)
					(*usb_midi_handleNoteOff)(ch, (n >> 16), (n >> 24));
			}
		} else
		if (type1 == 0x0A && type2 == 0x0A) {
			usb_midi_msg_type = 0xA0;		// 0xA0 = usbMIDI.AfterTouchPoly
			if (usb_midi_handleVelocityChange)
				(*usb_midi_handleVelocityChange)(ch, (n >> 16), (n >> 24));
		} else
		if (type1 == 0x0B && type2 == 0x0B) {
			usb_midi_msg_type = 0xB0;		// 0xB0 = usbMIDI.ControlChange
			if (usb_midi_handleControlChange)
				(*usb_midi_handleControlChange)(ch, (n >> 16), (n >> 24));
		} else
		if (type1 == 0x0C && type2 == 0x0C) {
			usb_midi_msg_type = 0xC0;		// 0xC0 = usbMIDI.ProgramChange
			if (usb_midi_handleProgramChange)
				(*usb_midi_handleProgramChange)(ch, (n >> 16));
		} else
		if (type1 == 0x0D && type2 == 0x0D) {
			usb_midi_msg_type = 0xD0;		// 0xD0 = usbMIDI.AfterTouchChannel
			if (usb_midi_handleAfterTouch)
				(*usb_midi_handleAfterTouch)(ch, (n >> 16));
		} else
		if (type1 == 0x0E && type2 == 0x0E) {
			usb_midi_msg_type = 0xE0;		// 0xE0 = usbMIDI.PitchBend
			if (usb_midi_handlePitchChange) {
				int value = ((n >> 16) & 0x7F) | ((n >> 17) & 0x3F80);
				value -= 8192; // 0 to 16383 --> -8192 to +8191
				(*usb_midi_handlePitchChange)(ch, value);
			}
		} else {
			return 0;
		}
		return_message:
		usb_midi_msg_channel = ch;
		usb_midi_msg_data1 = (n >> 16);
		usb_midi_msg_data2 = (n >> 24);
		return 1;
	}
	if (type1 == 0x02 || type1 == 0x03 || (type1 == 0x05 && b1 >= 0xF1 && b1 != 0xF7)) {
		// system common or system realtime message
		system_common_or_realtime:
		switch (b1) {
		  case 0xF1: // usbMIDI.TimeCodeQuarterFrame
			if (usb_midi_handleTimeCodeQuarterFrame) {
				(*usb_midi_handleTimeCodeQuarterFrame)(n >> 16);
			}
			break;
		  case 0xF2: // usbMIDI.SongPosition
			if (usb_midi_handleSongPosition) {
				(*usb_midi_handleSongPosition)(
				  ((n >> 16) & 0x7F) | ((n >> 17) & 0x3F80));
			}
			break;
		  case 0xF3: // usbMIDI.SongSelect
			if (usb_midi_handleSongSelect) {
				(*usb_midi_handleSongSelect)(n >> 16);
			}
			break;
		  case 0xF6: // usbMIDI.TuneRequest
			if (usb_midi_handleTuneRequest) {
				(*usb_midi_handleTuneRequest)();
			}
			break;
		  case 0xF8: // usbMIDI.Clock
			if (usb_midi_handleClock) {
				(*usb_midi_handleClock)();
			} else if (usb_midi_handleRealTimeSystem) {
				(*usb_midi_handleRealTimeSystem)(0xF8);
			}
			break;
		  case 0xFA: // usbMIDI.Start
			if (usb_midi_handleStart) {
				(*usb_midi_handleStart)();
			} else if (usb_midi_handleRealTimeSystem) {
				(*usb_midi_handleRealTimeSystem)(0xFA);
			}
			break;
		  case 0xFB: // usbMIDI.Continue
			if (usb_midi_handleContinue) {
				(*usb_midi_handleContinue)();
			} else if (usb_midi_handleRealTimeSystem) {
				(*usb_midi_handleRealTimeSystem)(0xFB);
			}
			break;
		  case 0xFC: // usbMIDI.Stop
			if (usb_midi_handleStop) {
				(*usb_midi_handleStop)();
			} else if (usb_midi_handleRealTimeSystem) {
				(*usb_midi_handleRealTimeSystem)(0xFC);
			}
			break;
		  case 0xFE: // usbMIDI.ActiveSensing
			if (usb_midi_handleActiveSensing) {
				(*usb_midi_handleActiveSensing)();
			} else if (usb_midi_handleRealTimeSystem) {
				(*usb_midi_handleRealTimeSystem)(0xFE);
			}
			break;
		  case 0xFF: // usbMIDI.SystemReset
			if (usb_midi_handleSystemReset) {
				(*usb_midi_handleSystemReset)();
			} else if (usb_midi_handleRealTimeSystem) {
				(*usb_midi_handleRealTimeSystem)(0xFF);
			}
			break;
		  default:
			return 0; // unknown message, ignore it
		}
		usb_midi_msg_type = b1;
		goto return_message;
	}
	if (type1 == 0x04) {
		sysex_byte(n >> 8);
		sysex_byte(n >> 16);
		sysex_byte(n >> 24);
		return 0;
	}
	if (type1 >= 0x05 && type1 <= 0x07) {
		sysex_byte(b1);
		if (type1 >= 0x06) sysex_byte(n >> 16);
		if (type1 == 0x07) sysex_byte(n >> 24);
		uint16_t len = usb_midi_msg_sysex_len;
		usb_midi_msg_data1 = len;
		usb_midi_msg_data2 = len >> 8;
		usb_midi_msg_sysex_len = 0;
		usb_midi_msg_type = 0xF0;			// 0xF0 = usbMIDI.SystemExclusive
		if (usb_midi_handleSysExPartial) {
			(*usb_midi_handleSysExPartial)(usb_midi_msg_sysex, len, 1);
		} else if (usb_midi_handleSysExComplete) {
			(*usb_midi_handleSysExComplete)(usb_midi_msg_sysex, len);
		}
		return 1;
	}
	if (type1 == 0x0F) {
		if (b1 >= 0xF8) {
			// From Sebastian Tomczak, seb.tomczak at gmail.com
			// http://little-scale.blogspot.com/2011/08/usb-midi-game-boy-sync-for-16.html
			goto system_common_or_realtime;
		}
		if (b1 == 0xF0 || usb_midi_msg_sysex_len > 0) {
			// From David Sorlien, dsorlien at gmail.com, http://axe4live.wordpress.com
			// OSX sometimes uses Single Byte Unparsed to
			// send bytes in the middle of a SYSEX message.
			sysex_byte(b1);
		}
	}
	return 0;
}


#endif // F_CPU
#endif // MIDI_INTERFACE

PaulStoffregen · Jun 20, 2023

This issue was discussed in detail on another thread:

https://forum.pjrc.com/threads/70288-usbMIDI-transmission-error

Teensy 3.6 USB midi sysex errors

rvh

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rvh

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rvh

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rvh

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rvh

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PaulStoffregen

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