MIDI file playback using the MPU-401? \ VOGONS

MIDI file playback using the MPU-401?

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First post, by superfury

Posted on 2015-02-28, 11:33

superfury Offline

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Rank: l33t++
Posts: 5465
Joined: 2014-03-08, 11:25
Location: Netherlands

I'm currently testing my MPU emulation (which is the Dosbox mpu.cpp as the 'front-end' and my own MIDI emulation (everything producing sound and processing the MIDI commands send to the output) as the 'backend'. I'm currently trying to get my .mid file playback correctly. I do get sound, but it seems to go very fast and crashes in the end:

1#include "headers/types.h"
2#include "headers/support/zalloc.h" //Zalloc support!
3#include "headers/hardware/ports.h" //MPU support!
4#include "headers/emu/timers.h" //Timer support!
5#include "headers/support/mid.h" //Our own typedefs!
6
7#define MIDIHEADER_ID 0x6468544d
8#define MIDIHEADER_TRACK_ID 0x6b72544d
9
10word byteswap16(word value)
11{
12	return ((value & 0xFF) << 8) | ((value & 0xFF00) >> 8); //Byteswap!
13}
14
15uint_32 byteswap32(uint_32 value)
16{
17	return (byteswap16(value & 0xFFFF) << 8) | byteswap16((value & 0xFFFF0000) >> 16); //
18}
19
20uint_32 activetempo = 0x500000; //Current tempo!
21
22word readMID(char *filename, HEADER_CHNK *header, TRACK_CHNK *tracks, byte **channels, word maxchannels)
23{
24	FILE *f;
25	TRACK_CHNK currenttrack;
26	TRACK_CHNK *curtracks = tracks;
27	word currenttrackn = 0; //Ammount of tracks loaded!
28	uint_32 tracklength;
29
30	byte *data;
31	f = fopen(filename, "rb"); //Try to open!
32	if (!f) return 0; //Error: file not found!
33	if (fread(header, 1, sizeof(*header), f) != sizeof(*header))
34	{
35		fclose(f);
36		return 0; //Error reading header!
37	}
38	if (header->Header != MIDIHEADER_ID)
39	{
40		fclose(f);
41		return 0; //Nothing!
42	}
43	if (byteswap32(header->header_length) != 6)
44	{
45		fclose(f);
46		return 0; //Nothing!
47	}
48	if (byteswap16(header->format)>1) //Not single/multiple tracks played simultaneously?
49	{
50		fclose(f);
51		return 0; //Not single track!
52	}
53	nexttrack: //Read the next track!
54	if (fread(&currenttrack, 1, sizeof(currenttrack), f) != sizeof(currenttrack)) //Error in track?
55	{
56		fclose(f);
57		return 0; //Invalid track!
58	}
59	if (currenttrack.Header != MIDIHEADER_TRACK_ID) //Not a track ID?
60	{

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61		fclose(f);
62		return 0; //Invalid track header!
63	}
64	if (!currenttrack.length) //No length?
65	{
66		fclose(f);
67		return 0; //Invalid track length!
68	}
69	tracklength = byteswap32(currenttrack.length); //Calculate the length of the track!
70	data = zalloc(tracklength,"MIDI_DATA"); //Allocate data!
71	if (!data) //Ran out of memory?
72	{
73		fclose(f);
74		return 0; //Ran out of memory!
75	}
76	if (fread(data, 1, tracklength, f) != tracklength) //Error reading data?
77	{
78		fclose(f);
79		freez((void **)&data, tracklength, "MIDI_DATA");
80		return 0; //Error reading data!
81	}
82
83	++currenttrackn; //Increase the number of tracks loaded!
84	if (currenttrackn > maxchannels) //Limit broken?
85	{
86		freez((void **)&data, tracklength, "MIDI_DATA");
87		return 0; //Limit broken: we can't store the file!
88	}
89
90	channels[currenttrackn - 1] = data; //Safe the pointer to the data!
91	memcpy(tracks, &currenttrack, sizeof(currenttrack)); //Copy track information!
92	++tracks; //Next track!
93	if (/*(byteswap16(header->format) > 0) &&*/ (currenttrackn<byteswap16(header->n))) //Format 1? Take all tracks!
94	{
95		goto nexttrack; //Next track to check!
96	}
97
98	/*if (!feof(f)) //Not @EOF when required?
99	{
100		fclose(f);
101		freez((void **)data, byteswap32(currenttrack.length), "MIDI_DATA"); //Release current if there!
102		return 0; //Incomplete file!
103	}*/
104	fclose(f);
105	activetempo = 500000; //Default = 120BPM = 500000 microseconds/quarter note!
106	return currenttrackn; //Give the result: the ammount of tracks loaded!
107}
108
109void freeMID(TRACK_CHNK *tracks, byte **channels, word numchannels)
110{
111	uint_32 channelnr;
112	for (channelnr = 0; channelnr < numchannels; channelnr++)
113	{
114		freez(&channels[channelnr], byteswap32(tracks[channelnr].length), "MIDI_DATA"); //Try to free!
115	}
116}
117
118byte consumeStream(byte **stream, byte *result)
119{
120	if (!memprotect(*stream, 1, "MIDI_DATA")) return 0; //Error: EOS!
121	*result = **stream; //Read!
122	++(*stream); //Increase pointer in the stream!
123	return 1; //Consumed!
124}
125
126byte peekStream(byte **stream, byte *result)
127{
128	if (!memprotect(*stream, 1, "MIDI_DATA")) return 0; //Error: EOS!
129	*result = *(*stream); //Consume a byte!
130	return 1; //Consumed!
131}
132
133byte read_VLV(byte **midi_stream, uint_32 *result)
134{
135	uint_32 temp = 0;
136	byte curdata;
137	if (!consumeStream(midi_stream, &curdata)) return 0; //Read first VLV failed?
138	for (;;) //Process/read the VLV!
139	{
140		temp |= (curdata & 0x7F); //Add to length!
141		if (!(curdata & 0x80)) break; //No byte to follow?
142		temp <<= 7; //Make some room for the next byte!
143		if (!consumeStream(midi_stream, &curdata)) return 0; //Read VLV failed?
144	}
145	*result = temp; //Give the result!
146	return 1; //OK!
147}
148
149float calcfreq(uint_32 tempo, HEADER_CHNK *header)
150{
151	float PPQN, speed;
152	byte frames;
153	byte subframes; //Pulses per quarter note!
154	word division;
155	division = byteswap16(header->division); //Byte swap!
156
157	if (division & 0x8000) //SMTPE?
158	{
159		frames = (float)((division >> 8)&0x7F); //Frames!
160		subframes = (float)(division & 0xFF); //Subframes!
161		speed = frames; //Default: we're the frames!
162		if (subframes)
163		{
164			//We don't use the tempo: our rate is fixed!
165			frames *= subframes; //The result in subframes/second!
166		}
167		speed = frames; //Use (sub)frames!
168	}
169	else
170	{
171		//PPQN method!
172		PPQN = (float)division; //Read PPQN!
173		speed = (float)tempo; //Convert to speed!
174		speed /= 1000000.0f; //Divide by 1 second!
175		speed /= PPQN; //Divide to get the ticks per second!
176		speed = 1.0f / speed; //Ammount per second!
177		speed *= 0.5f; //Divide by 2 for slower speed!
178	}
179	//We're counting in ticks!
180	return speed; //ticks per second!
181}
182
183//The protective semaphore for our flags!
184SDL_sem *MID_timing_pos_Lock = NULL; //Timing position lock!
185SDL_sem *MID_BPM_Lock = NULL; //BPM/Active tempo lock!
186
187uint_64 timing_pos = 0; //Current timing position!
188float BPM = 0.0f; //No BPM by default!
189
190void updateMIDTimer(HEADER_CHNK *header) //Request an update of our timer!
191{
192	addtimer(calcfreq(activetempo, header), (Handler)&timing_pos, "MID_tempotimer", 0, 2, MID_timing_pos_Lock); //Add a counter timer!
193}
194
195//The protective semaphore for the hardware!
196SDL_sem *MIDLock = NULL;
197
198#define MIDI_ERROR(position) {error = position; goto abortMIDI;}
199
200void playMIDIStream(word channel, byte *midi_stream, HEADER_CHNK *header)
201{
202	byte *curstream = midi_stream; //Copy the stream!
203	byte curdata;
204
205	//Metadata event!
206	byte meta_type;
207	uint_32 length; //Our metadata variable length!
208
209	uint_64 play_pos = 0; //Current play position!
210
211	uint_32 delta_time; //Delta time!
212
213	byte last_command = 0; //Last executed command!
214
215	int_32 error = 0; //Default: no error!
216	for (;;) //Playing?
217	{
218		//First, timing information and timing itself!
219		if (!read_VLV(&curstream, &delta_time)) return; //Read VLV time index!
220		play_pos += delta_time; //Add the delta time to the playing position!
221		for (;;)
222		{
223			//Lock
224			SDL_SemWait(MID_timing_pos_Lock);
225			if (timing_pos >= play_pos)
226			{
227				//Unlock
228				SDL_SemPost(MID_timing_pos_Lock);
229				break; //Arrived? Play!
230			}
231			//Unlock
232			SDL_SemPost(MID_timing_pos_Lock);
233			delay(0); //Wait for our tick!
234		}
235
236		if (!peekStream(&curstream, &curdata))
237		{
238			return; //Failed to peek!
239		}
240		if (curdata == 0xFF) //System?
241		{
242			if (!consumeStream(&curstream, &curdata)) return; //EOS!
243			if (!consumeStream(&curstream, &meta_type)) return; //Meta type failed? Give error!
244			if (!read_VLV(&curstream, &length)) return; //Error: unexpected EOS!
245			switch (meta_type) //What event?
246			{
247				case 0x2F: //EOT?
248					dolog("MID", "channel %i: EOT!", channel); //EOT reached!
249					return; //End of track reached: done!
250				case 0x51: //Set tempo?
251					//Lock
252					SDL_SemWait(MID_BPM_Lock);
253					removetimer("MID_tempotimer"); //Remove old timer!
254
255					if (!consumeStream(&curstream, &curdata)) return; //Tempo 1/3 failed?
256					activetempo = curdata; //Final byte!
257					activetempo <<= 8;
258					if (!consumeStream(&curstream, &curdata)) return; //Tempo 2/3 failed?
259					activetempo |= curdata; //Final byte!
260					activetempo <<= 8;
261					if (!consumeStream(&curstream, &curdata)) return; //Tempo 3/3 failed?
262					activetempo |= curdata; //Final byte!
263					//Tempo = us per quarter note!
264
265					updateMIDTimer(header);
266
267					dolog("MID", "channel %i: Set Tempo:%06X!", channel, activetempo);
268
269					//Unlock
270					SDL_SemPost(MID_BPM_Lock);
271					break;
272				default: //Unrecognised meta event? Skip it!
273					dolog("MID", "Unrecognised meta type: %02X@Channel %i; Data length: %i", meta_type, channel,length); //Log the unrecognised metadata type!
274					for (; length--;) //Process length bytes!
275					{
276						if (!consumeStream(&curstream, &curdata)) return; //Skip failed?
277					}
278					break;
279			}
280		}
281		else //Hardware?
282		{
283			//Lock
284			SDL_SemWait(MIDLock);
285
286			if (curdata & 0x80) //Starting a new command?
287			{
288				dolog("MID", "Status@Channel %i=%02X", channel, curdata);
289				if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(1) //EOS!
290				last_command = curdata; //Save the last command!
291				if (last_command != 0xF7) //Escaped continue isn't sent!
292				{
293					PORT_OUT_B(0x330, last_command); //Send the command!
294				}
295			}
296			else
297			{
298				dolog("MID", "Continued status@Channel %i: %02X=>%02X",channel, last_command, curdata);
299				if (last_command != 0xF7) //Escaped continue isn't used last?
300				{
301					PORT_OUT_B(0x330, last_command); //Repeat the status bytes: we don't know what the other channels do!
302				}
303			}
304
305			//Process the data for the command!
306			switch ((last_command >> 4) & 0xF) //What command to send data for?
307			{
308			case 0xF: //Special?
309				switch (last_command & 0xF) //What subcommand are we sending?
310				{
311				case 0x0: //System exclusive?
312				case 0x7: //Escaped continue?
313					if (!read_VLV(&curstream, &length)) MIDI_ERROR(2) //Error: unexpected EOS!
314					for (; length--;) //Transmit the packet!
315					{
316						if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(3+length) //EOS!
317						PORT_OUT_B(0x330, curdata); //Send the byte!
318					}
319					break;
320				case 0x1:
321				case 0x3:
322					//1 byte follows!
323					if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(2) //EOS!
324					PORT_OUT_B(0x330, curdata); //Passthrough to MIDI!
325					break;
326				case 0x2:
327					//2 bytes follow!
328					if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(2) //EOS!
329					PORT_OUT_B(0x330, curdata); //Passthrough to MIDI!
330					if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(3) //EOS!
331					PORT_OUT_B(0x330, curdata); //Passthrough to MIDI!
332					break;
333				default: //Unknown special instruction?
334					break; //Single byte instruction?
335				}
336				break;
337			case 0x8: //Note off?
338			case 0x9: //Note on?
339			case 0xA: //Aftertouch?
340			case 0xB: //Control change?
341			case 0xE: //Pitch bend?
342				//2 bytes follow!
343				if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(2) //EOS!
344				PORT_OUT_B(0x330, curdata); //Passthrough to MIDI!
345				if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(3) //EOS!
346				PORT_OUT_B(0x330, curdata); //Passthrough to MIDI!
347				break;
348			case 0xC: //Program change?
349			case 0xD: //Channel pressure/aftertouch?
350				//1 byte follows
351				if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(2) //EOS!
352				PORT_OUT_B(0x330, curdata); //Passthrough to MIDI!
353				break;
354			default: //Unknown data? We're sending directly to the hardware! We shouldn't be here!
355				if (!consumeStream(&curstream, &curdata)) MIDI_ERROR(2) //EOS!
356				dolog("MID", "Warning: Unknown data detected@channel %i: passthrough to MIDI device: %02X!",channel,curdata);
357				PORT_OUT_B(0x330, curdata); //Passthrough to MIDI!
358				break;
359			}
360		abortMIDI:
361			//Unlock
362			if (error)
363			{
364				dolog("MID", "channel %i: Error @position %i during MID processing! Unexpected EOS? Last command: %02X, Current data: %02X",channel,error,last_command,curdata);
365				SDL_SemPost(MIDLock); //Finish up!
366				return; //Abort on error!
367			}
368			SDL_SemPost(MIDLock); //Finish: prepare for next command!
369		}
370	}
371}

The loader:

1extern uint_64 timing_pos; //Current timing position for MIDI speed playback!
2
3word MID_RUNNING = 0;
4
5HEADER_CHNK header;
6
7SDL_sem *MID_channel_Lock = NULL; //Our channel lock for counting running MIDI!
8
9byte *MID_data[100]; //Tempo and music track!
10TRACK_CHNK MID_tracks[100];
11
12void handleMIDIChannel()
13{
14	word channel;
15	channel = (word)getthreadparams(); //Gotten a channel?
16	playMIDIStream(channel,MID_data[channel], &header); //Play the MIDI stream!
17	SDL_SemWait(MID_channel_Lock);
18	dolog("MID", "Channel %i finished", channel); //We're finished!
19	--MID_RUNNING; //Done!
20	SDL_SemPost(MID_channel_Lock);
21}
22
23//All used locks!
24extern SDL_sem *MIDLock;
25extern SDL_sem *MID_timing_pos_Lock;
26extern SDL_sem *MID_BPM_Lock;

...

1	memset(&MID_data, 0, sizeof(MID_data)); //Init data!
2	memset(&MID_tracks, 0, sizeof(MID_tracks)); //Init tracks!
3
4	word numchannels = 0;
5	if ((numchannels = readMID("MPU.mid", &header, &MID_tracks[0], &MID_data[0], 100)))
6	{
7		//Initialise our device!
8		PORT_OUT_B(0x331, 0xFF); //Reset!
9		PORT_OUT_B(0x331, 0x3F); //Kick to UART mode!
10		updateMIDTimer(&header); //Update the timer!
11
12		//Create the semaphore for the threads!
13		MIDLock = SDL_CreateSemaphore(1);
14		MID_timing_pos_Lock = SDL_CreateSemaphore(1);
15		MID_BPM_Lock = SDL_CreateSemaphore(1);
16		MID_channel_Lock = SDL_CreateSemaphore(1);
17
18		//Now, start up all timers!
19
20		word i;
21		MID_RUNNING = numchannels; //Init to all running!
22		for (i = 0; i < numchannels; i++)
23		{
24			startThread(&handleMIDIChannel, "MIDI_STREAM", (void *)i, DEFAULT_PRIORITY); //Start a thread handling the output of the channel!
25		}
26
27		delay(10000); //Wait a bit to allow for initialisation (position 0) to run!
28
29		startTimers(1);
30		startTimers(0); //Start our timers!
31
32		byte running = 1; //Are we running?
33
34		for (;;) //Wait to end!
35		{
36			delay(1000000); //Wait 1sec intervals!
37			SDL_SemWait(MID_channel_Lock);
38			if (!MID_RUNNING)
39			{
40				running = 0; //Not running anymore!
41			}
42			SDL_SemPost(MID_channel_Lock);
43			if (!running) break; //Not running anymore? Start quitting!
44		}
45
46		//Destroy semaphore
47		SDL_DestroySemaphore(MIDLock);
48		SDL_DestroySemaphore(MID_timing_pos_Lock);
49		SDL_DestroySemaphore(MID_BPM_Lock);
50		SDL_DestroySemaphore(MID_channel_Lock);
51
52		removetimer("MID_tempotimer"); //Clean up!
53		freeMID(&MID_tracks[0], &MID_data[0], numchannels); //Free all channels!
54		halt();
55		exit(0);
56		sleep();
57	}

What happens:
- The loader does the normal 'CPU' work.
- The midi channel processes a channel and send it to the MPU-401.
- The Dosbox mpu.cpp sends command and data bytes it to my emulated MIDI processing layer (Dosbox itself sends it to Windows/Unix etc.), since it's in UART mode.
- My MIDI processing layer processes command and sets them a command at a time to my playback engine.
- My MIDI playback engine handles everything to generate the sound:
- 1. Process the command and execute it.
- 2. Voice sound thread: Make the correct sound using the SoundFont backend and envelopes.

Anyone knows if the above parser is correct?

BTW, the delay(us) function delays the current thread. PORT_OUT_B(port,data) sends data to the MPU-401.

Author of the UniPCemu emulator.
UniPCemu Git repository
UniPCemu for Android, Windows, PSP, Vita and Switch on itch.io

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