snd_rawmidi_transmit — copy from the buffer to the device
int snd_rawmidi_transmit
(struct snd_rawmidi_substream * substream, unsigned char * buffer, int count);
the rawmidi substream
the buffer pointer
the data size to transfer
Copies data from the buffer to the device and advances the pointer.
Returns the copied size if successful, or a negative error code on failure.