sound/firewire/motu/amdtp-motu.c - linux - Git at Google

 /*
  * amdtp-motu.c - a part of driver for MOTU FireWire series
  *
  * Copyright (c) 2015-2017 Takashi Sakamoto <o-takashi@sakamocchi.jp>
  *
  * Licensed under the terms of the GNU General Public License, version 2.
  */

 #include <linux/slab.h>
 #include <sound/pcm.h>
 #include "motu.h"

 #define CREATE_TRACE_POINTS
 #include "amdtp-motu-trace.h"

 #define CIP_FMT_MOTU		0x02
 #define CIP_FMT_MOTU_TX_V3	0x22
 #define MOTU_FDF_AM824		0x22

 /*
  * 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

 struct amdtp_motu {
 	/* For timestamp processing.  */
 	unsigned int quotient_ticks_per_event;
 	unsigned int remainder_ticks_per_event;
 	unsigned int next_ticks;
 	unsigned int next_accumulated;
 	unsigned int next_cycles;
 	unsigned int next_seconds;

 	unsigned int pcm_chunks;
 	unsigned int pcm_byte_offset;

 	struct snd_rawmidi_substream *midi;
 	unsigned int midi_ports;
 	unsigned int midi_flag_offset;
 	unsigned int midi_byte_offset;

 	int midi_db_count;
 	unsigned int midi_db_interval;
 };

 int amdtp_motu_set_parameters(struct amdtp_stream *s, unsigned int rate,
 			      unsigned int midi_ports,
 			      struct snd_motu_packet_format *formats)
 {
 	static const struct {
 		unsigned int quotient_ticks_per_event;
 		unsigned int remainder_ticks_per_event;
 	} params[] = {
 		[CIP_SFC_44100]  = { 557, 123 },
 		[CIP_SFC_48000]  = { 512,   0 },
 		[CIP_SFC_88200]  = { 278, 282 },
 		[CIP_SFC_96000]  = { 256,   0 },
 		[CIP_SFC_176400] = { 139, 141 },
 		[CIP_SFC_192000] = { 128,   0 },
 	};
 	struct amdtp_motu *p = s->protocol;
 	unsigned int pcm_chunks, data_chunks, data_block_quadlets;
 	unsigned int delay;
 	unsigned int mode;
 	int i, err;

 	if (amdtp_stream_running(s))
 		return -EBUSY;

 	for (i = 0; i < ARRAY_SIZE(snd_motu_clock_rates); ++i) {
 		if (snd_motu_clock_rates[i] == rate) {
 			mode = i >> 1;
 			break;
 		}
 	}
 	if (i == ARRAY_SIZE(snd_motu_clock_rates))
 		return -EINVAL;

 	pcm_chunks = formats->fixed_part_pcm_chunks[mode] +
 		     formats->differed_part_pcm_chunks[mode];
 	data_chunks = formats->msg_chunks + pcm_chunks;

 	/*
 	 * Each data block includes SPH in its head. Data chunks follow with
 	 * 3 byte alignment. Padding follows with zero to conform to quadlet
 	 * alignment.
 	 */
 	data_block_quadlets = 1 + DIV_ROUND_UP(data_chunks * 3, 4);

 	err = amdtp_stream_set_parameters(s, rate, data_block_quadlets);
 	if (err < 0)
 		return err;

 	p->pcm_chunks = pcm_chunks;
 	p->pcm_byte_offset = formats->pcm_byte_offset;

 	p->midi_ports = midi_ports;
 	p->midi_flag_offset = formats->midi_flag_offset;
 	p->midi_byte_offset = formats->midi_byte_offset;

 	p->midi_db_count = 0;
 	p->midi_db_interval = rate / MIDI_BYTES_PER_SECOND;

 	/* IEEE 1394 bus requires. */
 	delay = 0x2e00;

 	/* For no-data or empty packets to adjust PCM sampling frequency. */
 	delay += 8000 * 3072 * s->syt_interval / rate;

 	p->next_seconds = 0;
 	p->next_cycles = delay / 3072;
 	p->quotient_ticks_per_event = params[s->sfc].quotient_ticks_per_event;
 	p->remainder_ticks_per_event = params[s->sfc].remainder_ticks_per_event;
 	p->next_ticks = delay % 3072;
 	p->next_accumulated = 0;

 	return 0;
 }

 static void read_pcm_s32(struct amdtp_stream *s,
 			 struct snd_pcm_runtime *runtime,
 			 __be32 *buffer, unsigned int data_blocks)
 {
 	struct amdtp_motu *p = s->protocol;
 	unsigned int channels, remaining_frames, i, c;
 	u8 *byte;
 	u32 *dst;

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

 	for (i = 0; i < data_blocks; ++i) {
 		byte = (u8 *)buffer + p->pcm_byte_offset;

 		for (c = 0; c < channels; ++c) {
 			*dst = (byte[0] << 24) | (byte[1] << 16) | byte[2];
 			byte += 3;
 			dst++;
 		}
 		buffer += s->data_block_quadlets;
 		if (--remaining_frames == 0)
 			dst = (void *)runtime->dma_area;
 	}
 }

 static void write_pcm_s32(struct amdtp_stream *s,
 			  struct snd_pcm_runtime *runtime,
 			  __be32 *buffer, unsigned int data_blocks)
 {
 	struct amdtp_motu *p = s->protocol;
 	unsigned int channels, remaining_frames, i, c;
 	u8 *byte;
 	const u32 *src;

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

 	for (i = 0; i < data_blocks; ++i) {
 		byte = (u8 *)buffer + p->pcm_byte_offset;

 		for (c = 0; c < channels; ++c) {
 			byte[0] = (*src >> 24) & 0xff;
 			byte[1] = (*src >> 16) & 0xff;
 			byte[2] = (*src >>  8) & 0xff;
 			byte += 3;
 			src++;
 		}

 		buffer += s->data_block_quadlets;
 		if (--remaining_frames == 0)
 			src = (void *)runtime->dma_area;
 	}
 }

 static void write_pcm_silence(struct amdtp_stream *s, __be32 *buffer,
 			      unsigned int data_blocks)
 {
 	struct amdtp_motu *p = s->protocol;
 	unsigned int channels, i, c;
 	u8 *byte;

 	channels = p->pcm_chunks;

 	for (i = 0; i < data_blocks; ++i) {
 		byte = (u8 *)buffer + p->pcm_byte_offset;

 		for (c = 0; c < channels; ++c) {
 			byte[0] = 0;
 			byte[1] = 0;
 			byte[2] = 0;
 			byte += 3;
 		}

 		buffer += s->data_block_quadlets;
 	}
 }

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

 	/* TODO: how to set an constraint for exactly 24bit PCM sample? */
 	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_motu_midi_trigger(struct amdtp_stream *s, unsigned int port,
 			     struct snd_rawmidi_substream *midi)
 {
 	struct amdtp_motu *p = s->protocol;

 	if (port < p->midi_ports)
 		WRITE_ONCE(p->midi, midi);
 }

 static void write_midi_messages(struct amdtp_stream *s, __be32 *buffer,
 				unsigned int data_blocks)
 {
 	struct amdtp_motu *p = s->protocol;
 	struct snd_rawmidi_substream *midi = READ_ONCE(p->midi);
 	u8 *b;
 	int i;

 	for (i = 0; i < data_blocks; i++) {
 		b = (u8 *)buffer;

 		if (midi && p->midi_db_count == 0 &&
 		    snd_rawmidi_transmit(midi, b + p->midi_byte_offset, 1) == 1) {
 			b[p->midi_flag_offset] = 0x01;
 		} else {
 			b[p->midi_byte_offset] = 0x00;
 			b[p->midi_flag_offset] = 0x00;
 		}

 		buffer += s->data_block_quadlets;

 		if (--p->midi_db_count < 0)
 			p->midi_db_count = p->midi_db_interval;
 	}
 }

 static void read_midi_messages(struct amdtp_stream *s, __be32 *buffer,
 			       unsigned int data_blocks)
 {
 	struct amdtp_motu *p = s->protocol;
 	struct snd_rawmidi_substream *midi;
 	u8 *b;
 	int i;

 	for (i = 0; i < data_blocks; i++) {
 		b = (u8 *)buffer;
 		midi = READ_ONCE(p->midi);

 		if (midi && (b[p->midi_flag_offset] & 0x01))
 			snd_rawmidi_receive(midi, b + p->midi_byte_offset, 1);

 		buffer += s->data_block_quadlets;
 	}
 }

 /* For tracepoints. */
 static void __maybe_unused copy_sph(u32 *frames, __be32 *buffer,
 				    unsigned int data_blocks,
 				    unsigned int data_block_quadlets)
 {
 	unsigned int i;

 	for (i = 0; i < data_blocks; ++i) {
 		*frames = be32_to_cpu(*buffer);
 		buffer += data_block_quadlets;
 		frames++;
 	}
 }

 /* For tracepoints. */
 static void __maybe_unused copy_message(u64 *frames, __be32 *buffer,
 					unsigned int data_blocks,
 					unsigned int data_block_quadlets)
 {
 	unsigned int i;

 	/* This is just for v2/v3 protocol. */
 	for (i = 0; i < data_blocks; ++i) {
 		*frames = (be32_to_cpu(buffer[1]) << 16) |
 			  (be32_to_cpu(buffer[2]) >> 16);
 		buffer += data_block_quadlets;
 		frames++;
 	}
 }

 static unsigned int process_tx_data_blocks(struct amdtp_stream *s,
 				__be32 *buffer, unsigned int data_blocks,
 				unsigned int *syt)
 {
 	struct amdtp_motu *p = s->protocol;
 	struct snd_pcm_substream *pcm;

 	trace_in_data_block_sph(s, data_blocks, buffer);
 	trace_in_data_block_message(s, data_blocks, buffer);

 	if (p->midi_ports)
 		read_midi_messages(s, buffer, data_blocks);

 	pcm = READ_ONCE(s->pcm);
 	if (data_blocks > 0 && pcm)
 		read_pcm_s32(s, pcm->runtime, buffer, data_blocks);

 	return data_blocks;
 }

 static inline void compute_next_elapse_from_start(struct amdtp_motu *p)
 {
 	p->next_accumulated += p->remainder_ticks_per_event;
 	if (p->next_accumulated >= 441) {
 		p->next_accumulated -= 441;
 		p->next_ticks++;
 	}

 	p->next_ticks += p->quotient_ticks_per_event;
 	if (p->next_ticks >= 3072) {
 		p->next_ticks -= 3072;
 		p->next_cycles++;
 	}

 	if (p->next_cycles >= 8000) {
 		p->next_cycles -= 8000;
 		p->next_seconds++;
 	}

 	if (p->next_seconds >= 128)
 		p->next_seconds -= 128;
 }

 static void write_sph(struct amdtp_stream *s, __be32 *buffer,
 		      unsigned int data_blocks)
 {
 	struct amdtp_motu *p = s->protocol;
 	unsigned int next_cycles;
 	unsigned int i;
 	u32 sph;

 	for (i = 0; i < data_blocks; i++) {
 		next_cycles = (s->start_cycle + p->next_cycles) % 8000;
 		sph = ((next_cycles << 12) | p->next_ticks) & 0x01ffffff;
 		*buffer = cpu_to_be32(sph);

 		compute_next_elapse_from_start(p);

 		buffer += s->data_block_quadlets;
 	}
 }

 static unsigned int process_rx_data_blocks(struct amdtp_stream *s,
 				__be32 *buffer, unsigned int data_blocks,
 				unsigned int *syt)
 {
 	struct amdtp_motu *p = (struct amdtp_motu *)s->protocol;
 	struct snd_pcm_substream *pcm;

 	/* Not used. */
 	*syt = 0xffff;

 	/* TODO: how to interact control messages between userspace? */

 	if (p->midi_ports)
 		write_midi_messages(s, buffer, data_blocks);

 	pcm = READ_ONCE(s->pcm);
 	if (pcm)
 		write_pcm_s32(s, pcm->runtime, buffer, data_blocks);
 	else
 		write_pcm_silence(s, buffer, data_blocks);

 	write_sph(s, buffer, data_blocks);

 	trace_out_data_block_sph(s, data_blocks, buffer);
 	trace_out_data_block_message(s, data_blocks, buffer);

 	return data_blocks;
 }

 int amdtp_motu_init(struct amdtp_stream *s, struct fw_unit *unit,
 		    enum amdtp_stream_direction dir,
 		    const struct snd_motu_protocol *const protocol)
 {
 	amdtp_stream_process_data_blocks_t process_data_blocks;
 	int fmt = CIP_FMT_MOTU;
 	int flags = CIP_BLOCKING;
 	int err;

 	if (dir == AMDTP_IN_STREAM) {
 		process_data_blocks = process_tx_data_blocks;

 		/*
 		 * Units of version 3 transmits packets with invalid CIP header
 		 * against IEC 61883-1.
 		 */
 		if (protocol == &snd_motu_protocol_v3) {
 			flags |= CIP_WRONG_DBS |
 				 CIP_SKIP_DBC_ZERO_CHECK |
 				 CIP_HEADER_WITHOUT_EOH;
 			fmt = CIP_FMT_MOTU_TX_V3;
 		}
 	} else {
 		process_data_blocks = process_rx_data_blocks;
 		flags |= CIP_DBC_IS_END_EVENT;
 	}

 	err = amdtp_stream_init(s, unit, dir, flags, fmt, process_data_blocks,
 				sizeof(struct amdtp_motu));
 	if (err < 0)
 		return err;

 	s->sph = 1;
 	s->fdf = MOTU_FDF_AM824;

 	return 0;
 }
	/*
	* amdtp-motu.c - a part of driver for MOTU FireWire series
	*
	* Copyright (c) 2015-2017 Takashi Sakamoto <o-takashi@sakamocchi.jp>
	*
	* Licensed under the terms of the GNU General Public License, version 2.
	*/

	#include <linux/slab.h>
	#include <sound/pcm.h>
	#include "motu.h"

	#define CREATE_TRACE_POINTS
	#include "amdtp-motu-trace.h"

	#define CIP_FMT_MOTU 0x02
	#define CIP_FMT_MOTU_TX_V3 0x22
	#define MOTU_FDF_AM824 0x22

	/*
	* 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

	struct amdtp_motu {
	/* For timestamp processing. */
	unsigned int quotient_ticks_per_event;
	unsigned int remainder_ticks_per_event;
	unsigned int next_ticks;
	unsigned int next_accumulated;
	unsigned int next_cycles;
	unsigned int next_seconds;

	unsigned int pcm_chunks;
	unsigned int pcm_byte_offset;

	struct snd_rawmidi_substream *midi;
	unsigned int midi_ports;
	unsigned int midi_flag_offset;
	unsigned int midi_byte_offset;

	int midi_db_count;
	unsigned int midi_db_interval;
	};

	int amdtp_motu_set_parameters(struct amdtp_stream *s, unsigned int rate,
	unsigned int midi_ports,
	struct snd_motu_packet_format *formats)
	{
	static const struct {
	unsigned int quotient_ticks_per_event;
	unsigned int remainder_ticks_per_event;
	} params[] = {
	[CIP_SFC_44100] = { 557, 123 },
	[CIP_SFC_48000] = { 512, 0 },
	[CIP_SFC_88200] = { 278, 282 },
	[CIP_SFC_96000] = { 256, 0 },
	[CIP_SFC_176400] = { 139, 141 },
	[CIP_SFC_192000] = { 128, 0 },
	};
	struct amdtp_motu *p = s->protocol;
	unsigned int pcm_chunks, data_chunks, data_block_quadlets;
	unsigned int delay;
	unsigned int mode;
	int i, err;

	if (amdtp_stream_running(s))
	return -EBUSY;

	for (i = 0; i < ARRAY_SIZE(snd_motu_clock_rates); ++i) {
	if (snd_motu_clock_rates[i] == rate) {
	mode = i >> 1;
	break;
	}
	}
	if (i == ARRAY_SIZE(snd_motu_clock_rates))
	return -EINVAL;

	pcm_chunks = formats->fixed_part_pcm_chunks[mode] +
	formats->differed_part_pcm_chunks[mode];
	data_chunks = formats->msg_chunks + pcm_chunks;

	/*
	* Each data block includes SPH in its head. Data chunks follow with
	* 3 byte alignment. Padding follows with zero to conform to quadlet
	* alignment.
	*/
	data_block_quadlets = 1 + DIV_ROUND_UP(data_chunks * 3, 4);

	err = amdtp_stream_set_parameters(s, rate, data_block_quadlets);
	if (err < 0)
	return err;

	p->pcm_chunks = pcm_chunks;
	p->pcm_byte_offset = formats->pcm_byte_offset;

	p->midi_ports = midi_ports;
	p->midi_flag_offset = formats->midi_flag_offset;
	p->midi_byte_offset = formats->midi_byte_offset;

	p->midi_db_count = 0;
	p->midi_db_interval = rate / MIDI_BYTES_PER_SECOND;

	/* IEEE 1394 bus requires. */
	delay = 0x2e00;

	/* For no-data or empty packets to adjust PCM sampling frequency. */
	delay += 8000 * 3072 * s->syt_interval / rate;

	p->next_seconds = 0;
	p->next_cycles = delay / 3072;
	p->quotient_ticks_per_event = params[s->sfc].quotient_ticks_per_event;
	p->remainder_ticks_per_event = params[s->sfc].remainder_ticks_per_event;
	p->next_ticks = delay % 3072;
	p->next_accumulated = 0;

	return 0;
	}

	static void read_pcm_s32(struct amdtp_stream *s,
	struct snd_pcm_runtime *runtime,
	__be32 *buffer, unsigned int data_blocks)
	{
	struct amdtp_motu *p = s->protocol;
	unsigned int channels, remaining_frames, i, c;
	u8 *byte;
	u32 *dst;

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

	for (i = 0; i < data_blocks; ++i) {
	byte = (u8 *)buffer + p->pcm_byte_offset;

	for (c = 0; c < channels; ++c) {
	*dst = (byte[0] << 24) \| (byte[1] << 16) \| byte[2];
	byte += 3;
	dst++;
	}
	buffer += s->data_block_quadlets;
	if (--remaining_frames == 0)
	dst = (void *)runtime->dma_area;
	}
	}

	static void write_pcm_s32(struct amdtp_stream *s,
	struct snd_pcm_runtime *runtime,
	__be32 *buffer, unsigned int data_blocks)
	{
	struct amdtp_motu *p = s->protocol;
	unsigned int channels, remaining_frames, i, c;
	u8 *byte;
	const u32 *src;

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

	for (i = 0; i < data_blocks; ++i) {
	byte = (u8 *)buffer + p->pcm_byte_offset;

	for (c = 0; c < channels; ++c) {
	byte[0] = (*src >> 24) & 0xff;
	byte[1] = (*src >> 16) & 0xff;
	byte[2] = (*src >> 8) & 0xff;
	byte += 3;
	src++;
	}

	buffer += s->data_block_quadlets;
	if (--remaining_frames == 0)
	src = (void *)runtime->dma_area;
	}
	}

	static void write_pcm_silence(struct amdtp_stream s, __be32 buffer,
	unsigned int data_blocks)
	{
	struct amdtp_motu *p = s->protocol;
	unsigned int channels, i, c;
	u8 *byte;

	channels = p->pcm_chunks;

	for (i = 0; i < data_blocks; ++i) {
	byte = (u8 *)buffer + p->pcm_byte_offset;

	for (c = 0; c < channels; ++c) {
	byte[0] = 0;
	byte[1] = 0;
	byte[2] = 0;
	byte += 3;
	}

	buffer += s->data_block_quadlets;
	}
	}

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

	/* TODO: how to set an constraint for exactly 24bit PCM sample? */
	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_motu_midi_trigger(struct amdtp_stream *s, unsigned int port,
	struct snd_rawmidi_substream *midi)
	{
	struct amdtp_motu *p = s->protocol;

	if (port < p->midi_ports)
	WRITE_ONCE(p->midi, midi);
	}

	static void write_midi_messages(struct amdtp_stream s, __be32 buffer,
	unsigned int data_blocks)
	{
	struct amdtp_motu *p = s->protocol;
	struct snd_rawmidi_substream *midi = READ_ONCE(p->midi);
	u8 *b;
	int i;

	for (i = 0; i < data_blocks; i++) {
	b = (u8 *)buffer;

	if (midi && p->midi_db_count == 0 &&
	snd_rawmidi_transmit(midi, b + p->midi_byte_offset, 1) == 1) {
	b[p->midi_flag_offset] = 0x01;
	} else {
	b[p->midi_byte_offset] = 0x00;
	b[p->midi_flag_offset] = 0x00;
	}

	buffer += s->data_block_quadlets;

	if (--p->midi_db_count < 0)
	p->midi_db_count = p->midi_db_interval;
	}
	}

	static void read_midi_messages(struct amdtp_stream s, __be32 buffer,
	unsigned int data_blocks)
	{
	struct amdtp_motu *p = s->protocol;
	struct snd_rawmidi_substream *midi;
	u8 *b;
	int i;

	for (i = 0; i < data_blocks; i++) {
	b = (u8 *)buffer;
	midi = READ_ONCE(p->midi);

	if (midi && (b[p->midi_flag_offset] & 0x01))
	snd_rawmidi_receive(midi, b + p->midi_byte_offset, 1);

	buffer += s->data_block_quadlets;
	}
	}

	/* For tracepoints. */
	static void __maybe_unused copy_sph(u32 frames, __be32 buffer,
	unsigned int data_blocks,
	unsigned int data_block_quadlets)
	{
	unsigned int i;

	for (i = 0; i < data_blocks; ++i) {
	frames = be32_to_cpu(buffer);
	buffer += data_block_quadlets;
	frames++;
	}
	}

	/* For tracepoints. */
	static void __maybe_unused copy_message(u64 frames, __be32 buffer,
	unsigned int data_blocks,
	unsigned int data_block_quadlets)
	{
	unsigned int i;

	/* This is just for v2/v3 protocol. */
	for (i = 0; i < data_blocks; ++i) {
	*frames = (be32_to_cpu(buffer[1]) << 16) \|
	(be32_to_cpu(buffer[2]) >> 16);
	buffer += data_block_quadlets;
	frames++;
	}
	}

	static unsigned int process_tx_data_blocks(struct amdtp_stream *s,
	__be32 *buffer, unsigned int data_blocks,
	unsigned int *syt)
	{
	struct amdtp_motu *p = s->protocol;
	struct snd_pcm_substream *pcm;

	trace_in_data_block_sph(s, data_blocks, buffer);
	trace_in_data_block_message(s, data_blocks, buffer);

	if (p->midi_ports)
	read_midi_messages(s, buffer, data_blocks);

	pcm = READ_ONCE(s->pcm);
	if (data_blocks > 0 && pcm)
	read_pcm_s32(s, pcm->runtime, buffer, data_blocks);

	return data_blocks;
	}

	static inline void compute_next_elapse_from_start(struct amdtp_motu *p)
	{
	p->next_accumulated += p->remainder_ticks_per_event;
	if (p->next_accumulated >= 441) {
	p->next_accumulated -= 441;
	p->next_ticks++;
	}

	p->next_ticks += p->quotient_ticks_per_event;
	if (p->next_ticks >= 3072) {
	p->next_ticks -= 3072;
	p->next_cycles++;
	}

	if (p->next_cycles >= 8000) {
	p->next_cycles -= 8000;
	p->next_seconds++;
	}

	if (p->next_seconds >= 128)
	p->next_seconds -= 128;
	}

	static void write_sph(struct amdtp_stream s, __be32 buffer,
	unsigned int data_blocks)
	{
	struct amdtp_motu *p = s->protocol;
	unsigned int next_cycles;
	unsigned int i;
	u32 sph;

	for (i = 0; i < data_blocks; i++) {
	next_cycles = (s->start_cycle + p->next_cycles) % 8000;
	sph = ((next_cycles << 12) \| p->next_ticks) & 0x01ffffff;
	*buffer = cpu_to_be32(sph);

	compute_next_elapse_from_start(p);

	buffer += s->data_block_quadlets;
	}
	}

	static unsigned int process_rx_data_blocks(struct amdtp_stream *s,
	__be32 *buffer, unsigned int data_blocks,
	unsigned int *syt)
	{
	struct amdtp_motu p = (struct amdtp_motu )s->protocol;
	struct snd_pcm_substream *pcm;

	/* Not used. */
	*syt = 0xffff;

	/* TODO: how to interact control messages between userspace? */

	if (p->midi_ports)
	write_midi_messages(s, buffer, data_blocks);

	pcm = READ_ONCE(s->pcm);
	if (pcm)
	write_pcm_s32(s, pcm->runtime, buffer, data_blocks);
	else
	write_pcm_silence(s, buffer, data_blocks);

	write_sph(s, buffer, data_blocks);

	trace_out_data_block_sph(s, data_blocks, buffer);
	trace_out_data_block_message(s, data_blocks, buffer);

	return data_blocks;
	}

	int amdtp_motu_init(struct amdtp_stream s, struct fw_unit unit,
	enum amdtp_stream_direction dir,
	const struct snd_motu_protocol *const protocol)
	{
	amdtp_stream_process_data_blocks_t process_data_blocks;
	int fmt = CIP_FMT_MOTU;
	int flags = CIP_BLOCKING;
	int err;

	if (dir == AMDTP_IN_STREAM) {
	process_data_blocks = process_tx_data_blocks;

	/*
	* Units of version 3 transmits packets with invalid CIP header
	* against IEC 61883-1.
	*/
	if (protocol == &snd_motu_protocol_v3) {
	flags \|= CIP_WRONG_DBS \|
	CIP_SKIP_DBC_ZERO_CHECK \|
	CIP_HEADER_WITHOUT_EOH;
	fmt = CIP_FMT_MOTU_TX_V3;
	}
	} else {
	process_data_blocks = process_rx_data_blocks;
	flags \|= CIP_DBC_IS_END_EVENT;
	}

	err = amdtp_stream_init(s, unit, dir, flags, fmt, process_data_blocks,
	sizeof(struct amdtp_motu));
	if (err < 0)
	return err;

	s->sph = 1;
	s->fdf = MOTU_FDF_AM824;

	return 0;
	}