Are you sending all 32 bytes, or only as many as are actually used? It's possible that the Windows driver ignore the entire USB packet when it sees an invalid event packet.

Good question Clemens! I tried to send 4bytes packets but it didn't work. Now I will try to complete a 32 bytes buffer and I'll tell you if it works. Than you for the suggest.

It didn't work.
Still having the same problem even with a complete 32Bytes buffer and a complete 64Bytes buffer.

Please show your source code.

Ok, I just rewrote a "generic" function that fills my tx buffer with only the necessary bytes (there's no check on max length since it's not necessary for this example code) to show you how I prepare the packets. Just checked and it works on mac OS (I tried on an old mac with yosemite OS and a new mac with catalina OS) but it doesn't work on windows (Windows 10). No issues with program changes or other standard "one/two/three bytes" messages.


Here' the code:

void USB_SYSEX_TX (unsigned char ID, unsigned char *tx_buf,unsigned char len)
{
unsigned char i = 0;
unsigned char tx_packets;
unsigned char last_packet_len = 0;
unsigned char buf_len;

len+=3; //Add F0, ID, F7

tx_packets = len/3;
last_packet_len = len - (tx_packets*3);
if (last_packet_len) tx_packets++;
buf_len = len + tx_packets;

if(!USBHandleBusy(USBTxHandle))
{
//First chunk
sysex_packet.v[0] = MIDI_CIN_SYSEX_START;
sysex_packet.v[1] = SysEx_START; //F0
sysex_packet.v[2] = ID;
sysex_packet.v[3] = tx_buf[0];

//middle chunks
for (i=1; i<tx_packets-1; i++)
{
sysex_packet.v[i*4] = MIDI_CIN_SYSEX_CONTINUE;
sysex_packet.v[(i*4)+1] = tx_buf[(i*3)-2];
sysex_packet.v[(i*4)+2] = tx_buf[(i*3)-1];
sysex_packet.v[(i*4)+3] = tx_buf[i*3];
}

//Last chunk
if (last_packet_len == 0)
{
sysex_packet.v[i*4] = MIDI_CIN_SYSEX_ENDS_3;
sysex_packet.v[(i*4)+1] = tx_buf[(i*3)-2];
sysex_packet.v[(i*4)+2] = tx_buf[(i*3)-1];
sysex_packet.v[(i*4)+3] = SysEx_END; //F7
}
else if (last_packet_len == 2)
{
sysex_packet.v[i*4] = MIDI_CIN_SYSEX_ENDS_2;
sysex_packet.v[(i*4)+1] = tx_buf[(i*3)-2];
sysex_packet.v[(i*4)+2] = SysEx_END; //F7
}
else if (last_packet_len == 1)
{
sysex_packet.v[i*4] = MIDI_CIN_SYSEX_ENDS_1;
sysex_packet.v[(i*4)+1] = SysEx_END; //F7
}

USBTxHandle = USBTxOnePacket(USB_DEVICE_AUDIO_MIDI_ENDPOINT,(uint8_t*)&sysex_packet,buf_len);
}
}

buf_len must be a multiple of four.

Thank you Clemens, I'll add a padding of 0s on the last chunk after the "sysex_end" and I'll try.

It worked! Buf_len now is multiple of four and I added a padding on the last chunk to complete the "fourtet". It works. Thank you for the support.