sound/firewire/digi00x/amdtp-dot.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * amdtp-dot.c - a part of driver for Digidesign Digi 002/003 family
  *
  * Copyright (c) 2014-2015 Takashi Sakamoto
  * Copyright (C) 2012 Robin Gareus <robin@gareus.org>
  * Copyright (C) 2012 Damien Zammit <damien@zamaudio.com>
  */

 #include <sound/pcm.h>
 #include "digi00x.h"

 #define CIP_FMT_AM		0x10

 /* 'Clock-based rate control mode' is just supported. */
 #define AMDTP_FDF_AM824		0x00

 /*
  * Nominally 3125 bytes/second, but the MIDI port's clock might be
  * 1% too slow, and the bus clock 100 ppm too fast.
  */
 #define MIDI_BYTES_PER_SECOND	3093

 /*
  * Several devices look only at the first eight data blocks.
  * In any case, this is more than enough for the MIDI data rate.
  */
 #define MAX_MIDI_RX_BLOCKS	8

 /* 3 = MAX(DOT_MIDI_IN_PORTS, DOT_MIDI_OUT_PORTS) + 1. */
 #define MAX_MIDI_PORTS		3

 /*
  * The double-oh-three algorithm was discovered by Robin Gareus and Damien
  * Zammit in 2012, with reverse-engineering for Digi 003 Rack.
  */
 struct dot_state {
 	u8 carry;
 	u8 idx;
 	unsigned int off;
 };

 struct amdtp_dot {
 	unsigned int pcm_channels;
 	struct dot_state state;

 	struct snd_rawmidi_substream *midi[MAX_MIDI_PORTS];
 	int midi_fifo_used[MAX_MIDI_PORTS];
 	int midi_fifo_limit;
 };

 /*
  * double-oh-three look up table
  *
  * @param idx index byte (audio-sample data) 0x00..0xff
  * @param off channel offset shift
  * @return salt to XOR with given data
  */
 #define BYTE_PER_SAMPLE (4)
 #define MAGIC_DOT_BYTE (2)
 #define MAGIC_BYTE_OFF(x) (((x) * BYTE_PER_SAMPLE) + MAGIC_DOT_BYTE)
 static u8 dot_scrt(const u8 idx, const unsigned int off)
 {
 	/*
 	 * the length of the added pattern only depends on the lower nibble
 	 * of the last non-zero data
 	 */
 	static const u8 len[16] = {0, 1, 3, 5, 7, 9, 11, 13, 14,
 				   12, 10, 8, 6, 4, 2, 0};

 	/*
 	 * the lower nibble of the salt. Interleaved sequence.
 	 * this is walked backwards according to len[]
 	 */
 	static const u8 nib[15] = {0x8, 0x7, 0x9, 0x6, 0xa, 0x5, 0xb, 0x4,
 				   0xc, 0x3, 0xd, 0x2, 0xe, 0x1, 0xf};

 	/* circular list for the salt's hi nibble. */
 	static const u8 hir[15] = {0x0, 0x6, 0xf, 0x8, 0x7, 0x5, 0x3, 0x4,
 				   0xc, 0xd, 0xe, 0x1, 0x2, 0xb, 0xa};

 	/*
 	 * start offset for upper nibble mapping.
 	 * note: 9 is /special/. In the case where the high nibble == 0x9,
 	 * hir[] is not used and - coincidentally - the salt's hi nibble is
 	 * 0x09 regardless of the offset.
 	 */
 	static const u8 hio[16] = {0, 11, 12, 6, 7, 5, 1, 4,
 				   3, 0x00, 14, 13, 8, 9, 10, 2};

 	const u8 ln = idx & 0xf;
 	const u8 hn = (idx >> 4) & 0xf;
 	const u8 hr = (hn == 0x9) ? 0x9 : hir[(hio[hn] + off) % 15];

 	if (len[ln] < off)
 		return 0x00;

 	return ((nib[14 + off - len[ln]]) | (hr << 4));
 }

 static void dot_encode_step(struct dot_state *state, __be32 *const buffer)
 {
 	u8 * const data = (u8 *) buffer;

 	if (data[MAGIC_DOT_BYTE] != 0x00) {
 		state->off = 0;
 		state->idx = data[MAGIC_DOT_BYTE] ^ state->carry;
 	}
 	data[MAGIC_DOT_BYTE] ^= state->carry;
 	state->carry = dot_scrt(state->idx, ++(state->off));
 }

 int amdtp_dot_set_parameters(struct amdtp_stream *s, unsigned int rate,
 			     unsigned int pcm_channels)
 {
 	struct amdtp_dot *p = s->protocol;
 	int err;

 	if (amdtp_stream_running(s))
 		return -EBUSY;

 	/*
 	 * A first data channel is for MIDI messages, the rest is Multi Bit
 	 * Linear Audio data channel.
 	 */
 	err = amdtp_stream_set_parameters(s, rate, pcm_channels + 1);
 	if (err < 0)
 		return err;

 	s->ctx_data.rx.fdf = AMDTP_FDF_AM824 | s->sfc;

 	p->pcm_channels = pcm_channels;

 	/*
 	 * We do not know the actual MIDI FIFO size of most devices.  Just
 	 * assume two bytes, i.e., one byte can be received over the bus while
 	 * the previous one is transmitted over MIDI.
 	 * (The value here is adjusted for midi_ratelimit_per_packet().)
 	 */
 	p->midi_fifo_limit = rate - MIDI_BYTES_PER_SECOND * s->syt_interval + 1;

 	return 0;
 }

 static void write_pcm_s32(struct amdtp_stream *s, struct snd_pcm_substream *pcm,
 			  __be32 *buffer, unsigned int frames,
 			  unsigned int pcm_frames)
 {
 	struct amdtp_dot *p = s->protocol;
 	unsigned int channels = p->pcm_channels;
 	struct snd_pcm_runtime *runtime = pcm->runtime;
 	unsigned int pcm_buffer_pointer;
 	int remaining_frames;
 	const u32 *src;
 	int i, c;

 	pcm_buffer_pointer = s->pcm_buffer_pointer + pcm_frames;
 	pcm_buffer_pointer %= runtime->buffer_size;

 	src = (void *)runtime->dma_area +
 				frames_to_bytes(runtime, pcm_buffer_pointer);
 	remaining_frames = runtime->buffer_size - pcm_buffer_pointer;

 	buffer++;
 	for (i = 0; i < frames; ++i) {
 		for (c = 0; c < channels; ++c) {
 			buffer[c] = cpu_to_be32((*src >> 8) | 0x40000000);
 			dot_encode_step(&p->state, &buffer[c]);
 			src++;
 		}
 		buffer += s->data_block_quadlets;
 		if (--remaining_frames == 0)
 			src = (void *)runtime->dma_area;
 	}
 }

 static void read_pcm_s32(struct amdtp_stream *s, struct snd_pcm_substream *pcm,
 			 __be32 *buffer, unsigned int frames,
 			 unsigned int pcm_frames)
 {
 	struct amdtp_dot *p = s->protocol;
 	unsigned int channels = p->pcm_channels;
 	struct snd_pcm_runtime *runtime = pcm->runtime;
 	unsigned int pcm_buffer_pointer;
 	int remaining_frames;
 	u32 *dst;
 	int i, c;

 	pcm_buffer_pointer = s->pcm_buffer_pointer + pcm_frames;
 	pcm_buffer_pointer %= runtime->buffer_size;

 	dst  = (void *)runtime->dma_area +
 				frames_to_bytes(runtime, pcm_buffer_pointer);
 	remaining_frames = runtime->buffer_size - pcm_buffer_pointer;

 	buffer++;
 	for (i = 0; i < frames; ++i) {
 		for (c = 0; c < channels; ++c) {
 			*dst = be32_to_cpu(buffer[c]) << 8;
 			dst++;
 		}
 		buffer += s->data_block_quadlets;
 		if (--remaining_frames == 0)
 			dst = (void *)runtime->dma_area;
 	}
 }

 static void write_pcm_silence(struct amdtp_stream *s, __be32 *buffer,
 			      unsigned int data_blocks)
 {
 	struct amdtp_dot *p = s->protocol;
 	unsigned int channels, i, c;

 	channels = p->pcm_channels;

 	buffer++;
 	for (i = 0; i < data_blocks; ++i) {
 		for (c = 0; c < channels; ++c)
 			buffer[c] = cpu_to_be32(0x40000000);
 		buffer += s->data_block_quadlets;
 	}
 }

 static bool midi_ratelimit_per_packet(struct amdtp_stream *s, unsigned int port)
 {
 	struct amdtp_dot *p = s->protocol;
 	int used;

 	used = p->midi_fifo_used[port];
 	if (used == 0)
 		return true;

 	used -= MIDI_BYTES_PER_SECOND * s->syt_interval;
 	used = max(used, 0);
 	p->midi_fifo_used[port] = used;

 	return used < p->midi_fifo_limit;
 }

 static inline void midi_use_bytes(struct amdtp_stream *s,
 				  unsigned int port, unsigned int count)
 {
 	struct amdtp_dot *p = s->protocol;

 	p->midi_fifo_used[port] += amdtp_rate_table[s->sfc] * count;
 }

 static void write_midi_messages(struct amdtp_stream *s, __be32 *buffer,
 		unsigned int data_blocks, unsigned int data_block_counter)
 {
 	struct amdtp_dot *p = s->protocol;
 	unsigned int f, port;
 	int len;
 	u8 *b;

 	for (f = 0; f < data_blocks; f++) {
 		port = (data_block_counter + f) % 8;
 		b = (u8 *)&buffer[0];

 		len = 0;
 		if (port < MAX_MIDI_PORTS &&
 		    midi_ratelimit_per_packet(s, port) &&
 		    p->midi[port] != NULL)
 			len = snd_rawmidi_transmit(p->midi[port], b + 1, 2);

 		if (len > 0) {
 			/*
 			 * Upper 4 bits of LSB represent port number.
 			 * - 0000b: physical MIDI port 1.
 			 * - 0010b: physical MIDI port 2.
 			 * - 1110b: console MIDI port.
 			 */
 			if (port == 2)
 				b[3] = 0xe0;
 			else if (port == 1)
 				b[3] = 0x20;
 			else
 				b[3] = 0x00;
 			b[3] |= len;
 			midi_use_bytes(s, port, len);
 		} else {
 			b[1] = 0;
 			b[2] = 0;
 			b[3] = 0;
 		}
 		b[0] = 0x80;

 		buffer += s->data_block_quadlets;
 	}
 }

 static void read_midi_messages(struct amdtp_stream *s, __be32 *buffer,
 			       unsigned int data_blocks)
 {
 	struct amdtp_dot *p = s->protocol;
 	unsigned int f, port, len;
 	u8 *b;

 	for (f = 0; f < data_blocks; f++) {
 		b = (u8 *)&buffer[0];

 		len = b[3] & 0x0f;
 		if (len > 0) {
 			/*
 			 * Upper 4 bits of LSB represent port number.
 			 * - 0000b: physical MIDI port 1. Use port 0.
 			 * - 1110b: console MIDI port. Use port 2.
 			 */
 			if (b[3] >> 4 > 0)
 				port = 2;
 			else
 				port = 0;

 			if (port < MAX_MIDI_PORTS && p->midi[port])
 				snd_rawmidi_receive(p->midi[port], b + 1, len);
 		}

 		buffer += s->data_block_quadlets;
 	}
 }

 int amdtp_dot_add_pcm_hw_constraints(struct amdtp_stream *s,
 				     struct snd_pcm_runtime *runtime)
 {
 	int err;

 	/* This protocol delivers 24 bit data in 32bit data channel. */
 	err = snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
 	if (err < 0)
 		return err;

 	return amdtp_stream_add_pcm_hw_constraints(s, runtime);
 }

 void amdtp_dot_midi_trigger(struct amdtp_stream *s, unsigned int port,
 			  struct snd_rawmidi_substream *midi)
 {
 	struct amdtp_dot *p = s->protocol;

 	if (port < MAX_MIDI_PORTS)
 		WRITE_ONCE(p->midi[port], midi);
 }

 static unsigned int process_ir_ctx_payloads(struct amdtp_stream *s,
 					    const struct pkt_desc *descs,
 					    unsigned int packets,
 					    struct snd_pcm_substream *pcm)
 {
 	unsigned int pcm_frames = 0;
 	int i;

 	for (i = 0; i < packets; ++i) {
 		const struct pkt_desc *desc = descs + i;
 		__be32 *buf = desc->ctx_payload;
 		unsigned int data_blocks = desc->data_blocks;

 		if (pcm) {
 			read_pcm_s32(s, pcm, buf, data_blocks, pcm_frames);
 			pcm_frames += data_blocks;
 		}

 		read_midi_messages(s, buf, data_blocks);
 	}

 	return pcm_frames;
 }

 static unsigned int process_it_ctx_payloads(struct amdtp_stream *s,
 					    const struct pkt_desc *descs,
 					    unsigned int packets,
 					    struct snd_pcm_substream *pcm)
 {
 	unsigned int pcm_frames = 0;
 	int i;

 	for (i = 0; i < packets; ++i) {
 		const struct pkt_desc *desc = descs + i;
 		__be32 *buf = desc->ctx_payload;
 		unsigned int data_blocks = desc->data_blocks;

 		if (pcm) {
 			write_pcm_s32(s, pcm, buf, data_blocks, pcm_frames);
 			pcm_frames += data_blocks;
 		} else {
 			write_pcm_silence(s, buf, data_blocks);
 		}

 		write_midi_messages(s, buf, data_blocks,
 				    desc->data_block_counter);
 	}

 	return pcm_frames;
 }

 int amdtp_dot_init(struct amdtp_stream *s, struct fw_unit *unit,
 		 enum amdtp_stream_direction dir)
 {
 	amdtp_stream_process_ctx_payloads_t process_ctx_payloads;
 	enum cip_flags flags;

 	// Use different mode between incoming/outgoing.
 	if (dir == AMDTP_IN_STREAM) {
 		flags = CIP_NONBLOCKING;
 		process_ctx_payloads = process_ir_ctx_payloads;
 	} else {
 		flags = CIP_BLOCKING;
 		process_ctx_payloads = process_it_ctx_payloads;
 	}

 	return amdtp_stream_init(s, unit, dir, flags, CIP_FMT_AM,
 				process_ctx_payloads, sizeof(struct amdtp_dot));
 }

 void amdtp_dot_reset(struct amdtp_stream *s)
 {
 	struct amdtp_dot *p = s->protocol;

 	p->state.carry = 0x00;
 	p->state.idx = 0x00;
 	p->state.off = 0;
 }
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* amdtp-dot.c - a part of driver for Digidesign Digi 002/003 family
	*
	* Copyright (c) 2014-2015 Takashi Sakamoto
	* Copyright (C) 2012 Robin Gareus <robin@gareus.org>
	* Copyright (C) 2012 Damien Zammit <damien@zamaudio.com>
	*/

	#include <sound/pcm.h>
	#include "digi00x.h"

	#define CIP_FMT_AM 0x10

	/* 'Clock-based rate control mode' is just supported. */
	#define AMDTP_FDF_AM824 0x00

	/*
	* Nominally 3125 bytes/second, but the MIDI port's clock might be
	* 1% too slow, and the bus clock 100 ppm too fast.
	*/
	#define MIDI_BYTES_PER_SECOND 3093

	/*
	* Several devices look only at the first eight data blocks.
	* In any case, this is more than enough for the MIDI data rate.
	*/
	#define MAX_MIDI_RX_BLOCKS 8

	/* 3 = MAX(DOT_MIDI_IN_PORTS, DOT_MIDI_OUT_PORTS) + 1. */
	#define MAX_MIDI_PORTS 3

	/*
	* The double-oh-three algorithm was discovered by Robin Gareus and Damien
	* Zammit in 2012, with reverse-engineering for Digi 003 Rack.
	*/
	struct dot_state {
	u8 carry;
	u8 idx;
	unsigned int off;
	};

	struct amdtp_dot {
	unsigned int pcm_channels;
	struct dot_state state;

	struct snd_rawmidi_substream *midi[MAX_MIDI_PORTS];
	int midi_fifo_used[MAX_MIDI_PORTS];
	int midi_fifo_limit;
	};

	/*
	* double-oh-three look up table
	*
	* @param idx index byte (audio-sample data) 0x00..0xff
	* @param off channel offset shift
	* @return salt to XOR with given data
	*/
	#define BYTE_PER_SAMPLE (4)
	#define MAGIC_DOT_BYTE (2)
	#define MAGIC_BYTE_OFF(x) (((x) * BYTE_PER_SAMPLE) + MAGIC_DOT_BYTE)
	static u8 dot_scrt(const u8 idx, const unsigned int off)
	{
	/*
	* the length of the added pattern only depends on the lower nibble
	* of the last non-zero data
	*/
	static const u8 len[16] = {0, 1, 3, 5, 7, 9, 11, 13, 14,
	12, 10, 8, 6, 4, 2, 0};

	/*
	* the lower nibble of the salt. Interleaved sequence.
	* this is walked backwards according to len[]
	*/
	static const u8 nib[15] = {0x8, 0x7, 0x9, 0x6, 0xa, 0x5, 0xb, 0x4,
	0xc, 0x3, 0xd, 0x2, 0xe, 0x1, 0xf};

	/* circular list for the salt's hi nibble. */
	static const u8 hir[15] = {0x0, 0x6, 0xf, 0x8, 0x7, 0x5, 0x3, 0x4,
	0xc, 0xd, 0xe, 0x1, 0x2, 0xb, 0xa};

	/*
	* start offset for upper nibble mapping.
	* note: 9 is /special/. In the case where the high nibble == 0x9,
	* hir[] is not used and - coincidentally - the salt's hi nibble is
	* 0x09 regardless of the offset.
	*/
	static const u8 hio[16] = {0, 11, 12, 6, 7, 5, 1, 4,
	3, 0x00, 14, 13, 8, 9, 10, 2};

	const u8 ln = idx & 0xf;
	const u8 hn = (idx >> 4) & 0xf;
	const u8 hr = (hn == 0x9) ? 0x9 : hir[(hio[hn] + off) % 15];

	if (len[ln] < off)
	return 0x00;

	return ((nib[14 + off - len[ln]]) \| (hr << 4));
	}

	static void dot_encode_step(struct dot_state state, __be32 const buffer)
	{
	u8 * const data = (u8 *) buffer;

	if (data[MAGIC_DOT_BYTE] != 0x00) {
	state->off = 0;
	state->idx = data[MAGIC_DOT_BYTE] ^ state->carry;
	}
	data[MAGIC_DOT_BYTE] ^= state->carry;
	state->carry = dot_scrt(state->idx, ++(state->off));
	}

	int amdtp_dot_set_parameters(struct amdtp_stream *s, unsigned int rate,
	unsigned int pcm_channels)
	{
	struct amdtp_dot *p = s->protocol;
	int err;

	if (amdtp_stream_running(s))
	return -EBUSY;

	/*
	* A first data channel is for MIDI messages, the rest is Multi Bit
	* Linear Audio data channel.
	*/
	err = amdtp_stream_set_parameters(s, rate, pcm_channels + 1);
	if (err < 0)
	return err;

	s->ctx_data.rx.fdf = AMDTP_FDF_AM824 \| s->sfc;

	p->pcm_channels = pcm_channels;

	/*
	* We do not know the actual MIDI FIFO size of most devices. Just
	* assume two bytes, i.e., one byte can be received over the bus while
	* the previous one is transmitted over MIDI.
	* (The value here is adjusted for midi_ratelimit_per_packet().)
	*/
	p->midi_fifo_limit = rate - MIDI_BYTES_PER_SECOND * s->syt_interval + 1;

	return 0;
	}

	static void write_pcm_s32(struct amdtp_stream s, struct snd_pcm_substream pcm,
	__be32 *buffer, unsigned int frames,
	unsigned int pcm_frames)
	{
	struct amdtp_dot *p = s->protocol;
	unsigned int channels = p->pcm_channels;
	struct snd_pcm_runtime *runtime = pcm->runtime;
	unsigned int pcm_buffer_pointer;
	int remaining_frames;
	const u32 *src;
	int i, c;

	pcm_buffer_pointer = s->pcm_buffer_pointer + pcm_frames;
	pcm_buffer_pointer %= runtime->buffer_size;

	src = (void *)runtime->dma_area +
	frames_to_bytes(runtime, pcm_buffer_pointer);
	remaining_frames = runtime->buffer_size - pcm_buffer_pointer;

	buffer++;
	for (i = 0; i < frames; ++i) {
	for (c = 0; c < channels; ++c) {
	buffer[c] = cpu_to_be32((*src >> 8) \| 0x40000000);
	dot_encode_step(&p->state, &buffer[c]);
	src++;
	}
	buffer += s->data_block_quadlets;
	if (--remaining_frames == 0)
	src = (void *)runtime->dma_area;
	}
	}

	static void read_pcm_s32(struct amdtp_stream s, struct snd_pcm_substream pcm,
	__be32 *buffer, unsigned int frames,
	unsigned int pcm_frames)
	{
	struct amdtp_dot *p = s->protocol;
	unsigned int channels = p->pcm_channels;
	struct snd_pcm_runtime *runtime = pcm->runtime;
	unsigned int pcm_buffer_pointer;
	int remaining_frames;
	u32 *dst;
	int i, c;

	pcm_buffer_pointer = s->pcm_buffer_pointer + pcm_frames;
	pcm_buffer_pointer %= runtime->buffer_size;

	dst = (void *)runtime->dma_area +
	frames_to_bytes(runtime, pcm_buffer_pointer);
	remaining_frames = runtime->buffer_size - pcm_buffer_pointer;

	buffer++;
	for (i = 0; i < frames; ++i) {
	for (c = 0; c < channels; ++c) {
	*dst = be32_to_cpu(buffer[c]) << 8;
	dst++;
	}
	buffer += s->data_block_quadlets;
	if (--remaining_frames == 0)
	dst = (void *)runtime->dma_area;
	}
	}

	static void write_pcm_silence(struct amdtp_stream s, __be32 buffer,
	unsigned int data_blocks)
	{
	struct amdtp_dot *p = s->protocol;
	unsigned int channels, i, c;

	channels = p->pcm_channels;

	buffer++;
	for (i = 0; i < data_blocks; ++i) {
	for (c = 0; c < channels; ++c)
	buffer[c] = cpu_to_be32(0x40000000);
	buffer += s->data_block_quadlets;
	}
	}

	static bool midi_ratelimit_per_packet(struct amdtp_stream *s, unsigned int port)
	{
	struct amdtp_dot *p = s->protocol;
	int used;

	used = p->midi_fifo_used[port];
	if (used == 0)
	return true;

	used -= MIDI_BYTES_PER_SECOND * s->syt_interval;
	used = max(used, 0);
	p->midi_fifo_used[port] = used;

	return used < p->midi_fifo_limit;
	}

	static inline void midi_use_bytes(struct amdtp_stream *s,
	unsigned int port, unsigned int count)
	{
	struct amdtp_dot *p = s->protocol;

	p->midi_fifo_used[port] += amdtp_rate_table[s->sfc] * count;
	}

	static void write_midi_messages(struct amdtp_stream s, __be32 buffer,
	unsigned int data_blocks, unsigned int data_block_counter)
	{
	struct amdtp_dot *p = s->protocol;
	unsigned int f, port;
	int len;
	u8 *b;

	for (f = 0; f < data_blocks; f++) {
	port = (data_block_counter + f) % 8;
	b = (u8 *)&buffer[0];

	len = 0;
	if (port < MAX_MIDI_PORTS &&
	midi_ratelimit_per_packet(s, port) &&
	p->midi[port] != NULL)
	len = snd_rawmidi_transmit(p->midi[port], b + 1, 2);

	if (len > 0) {
	/*
	* Upper 4 bits of LSB represent port number.
	* - 0000b: physical MIDI port 1.
	* - 0010b: physical MIDI port 2.
	* - 1110b: console MIDI port.
	*/
	if (port == 2)
	b[3] = 0xe0;
	else if (port == 1)
	b[3] = 0x20;
	else
	b[3] = 0x00;
	b[3] \|= len;
	midi_use_bytes(s, port, len);
	} else {
	b[1] = 0;
	b[2] = 0;
	b[3] = 0;
	}
	b[0] = 0x80;

	buffer += s->data_block_quadlets;
	}
	}

	static void read_midi_messages(struct amdtp_stream s, __be32 buffer,
	unsigned int data_blocks)
	{
	struct amdtp_dot *p = s->protocol;
	unsigned int f, port, len;
	u8 *b;

	for (f = 0; f < data_blocks; f++) {
	b = (u8 *)&buffer[0];

	len = b[3] & 0x0f;
	if (len > 0) {
	/*
	* Upper 4 bits of LSB represent port number.
	* - 0000b: physical MIDI port 1. Use port 0.
	* - 1110b: console MIDI port. Use port 2.
	*/
	if (b[3] >> 4 > 0)
	port = 2;
	else
	port = 0;

	if (port < MAX_MIDI_PORTS && p->midi[port])
	snd_rawmidi_receive(p->midi[port], b + 1, len);
	}

	buffer += s->data_block_quadlets;
	}
	}

	int amdtp_dot_add_pcm_hw_constraints(struct amdtp_stream *s,
	struct snd_pcm_runtime *runtime)
	{
	int err;

	/* This protocol delivers 24 bit data in 32bit data channel. */
	err = snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
	if (err < 0)
	return err;

	return amdtp_stream_add_pcm_hw_constraints(s, runtime);
	}

	void amdtp_dot_midi_trigger(struct amdtp_stream *s, unsigned int port,
	struct snd_rawmidi_substream *midi)
	{
	struct amdtp_dot *p = s->protocol;

	if (port < MAX_MIDI_PORTS)
	WRITE_ONCE(p->midi[port], midi);
	}

	static unsigned int process_ir_ctx_payloads(struct amdtp_stream *s,
	const struct pkt_desc *descs,
	unsigned int packets,
	struct snd_pcm_substream *pcm)
	{
	unsigned int pcm_frames = 0;
	int i;

	for (i = 0; i < packets; ++i) {
	const struct pkt_desc *desc = descs + i;
	__be32 *buf = desc->ctx_payload;
	unsigned int data_blocks = desc->data_blocks;

	if (pcm) {
	read_pcm_s32(s, pcm, buf, data_blocks, pcm_frames);
	pcm_frames += data_blocks;
	}

	read_midi_messages(s, buf, data_blocks);
	}

	return pcm_frames;
	}

	static unsigned int process_it_ctx_payloads(struct amdtp_stream *s,
	const struct pkt_desc *descs,
	unsigned int packets,
	struct snd_pcm_substream *pcm)
	{
	unsigned int pcm_frames = 0;
	int i;

	for (i = 0; i < packets; ++i) {
	const struct pkt_desc *desc = descs + i;
	__be32 *buf = desc->ctx_payload;
	unsigned int data_blocks = desc->data_blocks;

	if (pcm) {
	write_pcm_s32(s, pcm, buf, data_blocks, pcm_frames);
	pcm_frames += data_blocks;
	} else {
	write_pcm_silence(s, buf, data_blocks);
	}

	write_midi_messages(s, buf, data_blocks,
	desc->data_block_counter);
	}

	return pcm_frames;
	}

	int amdtp_dot_init(struct amdtp_stream s, struct fw_unit unit,
	enum amdtp_stream_direction dir)
	{
	amdtp_stream_process_ctx_payloads_t process_ctx_payloads;
	enum cip_flags flags;

	// Use different mode between incoming/outgoing.
	if (dir == AMDTP_IN_STREAM) {
	flags = CIP_NONBLOCKING;
	process_ctx_payloads = process_ir_ctx_payloads;
	} else {
	flags = CIP_BLOCKING;
	process_ctx_payloads = process_it_ctx_payloads;
	}

	return amdtp_stream_init(s, unit, dir, flags, CIP_FMT_AM,
	process_ctx_payloads, sizeof(struct amdtp_dot));
	}

	void amdtp_dot_reset(struct amdtp_stream *s)
	{
	struct amdtp_dot *p = s->protocol;

	p->state.carry = 0x00;
	p->state.idx = 0x00;
	p->state.off = 0;
	}