shithub: opl2

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use opl2's actual sampling rate and don't buffer output

- don't buffer output: rather than loop and use bio(2), just generate
all at once and write immediately; this fixes realtime applications
(from umbraticus' merged patch for games/opl3).
- sanity checks and exit status
- the opl2 chip has a weird sampling rate of 49.716kHz.  output rate
is still audio(3)'s default 44.1kHz, and input rate is arbitrary
(ultima6 m files: 60Hz, doom: same as opl chip).  instead of
implementing downsampling ourselves, we let pcmconv take care of it.

--- a/man/1/opl2

+++ b/man/1/opl2

@@ -4,8 +4,8 @@

 .SH SYNOPSIS

 .B opl2

 [

-.B -n

-.I rate

+.B -r

+.I input rate

 ] [

 .I file

 ]

@@ -17,10 +17,12 @@

 The emulated chip is programmed by a stream of commands either from

 .I file

 or from standard in.

-Guided by these commands, it then synthesizes a number of 16 bit little-endian samples for a sampling rate of 44.1 kHz.

+Guided by these commands, it then synthesizes a number of 16 bit little-endian samples for

+the chip's output sampling rate, 49.716 kHz.

 Each is duplicated for stereo sound and written to standard out.

 .PP

-Commands are 4 bytes formatted as follows, where the size of each field is given in bytes between brackets:

+Commands are 4 bytes formatted as follows,

+where the size of each field is given in bytes between brackets:

 .PP

 .RS

 .IR register [1]

@@ -43,37 +45,43 @@

 It is a multiple of a command period, during which the

 .SM OPL2

 chip may be sampled before processing the next command.

-The period itself is the inverse of the command rate, 700 Hz by default.

-This rate can be set using the

-.B -n

-parameter.

+The period itself is the inverse of the input stream's sampling rate,

+by default the same as the chip's output sampling rate.

+The

+.B -r

+parameter

+sets the input sampling rate.

 .SH EXAMPLES

 Use with Wolfenstein 3D IMF files (default rate):

 .IP

 .EX

-% opl2 -n 700 <imf >/dev/audio

+% opl2 -r 700 <imf >/dev/audio

 .EE

 .PP

 Use with Commander Keen IMF files:

 .IP

 .EX

-% opl2 -n 560 <imf >/dev/audio

+% opl2 -r 560 <imf >/dev/audio

 .EE

 .PP

 Use with Wolfenstein 3D adlib sound effects:

 .IP

 .EX

-% opl2 -n 140 <al >/dev/audio

+% opl2 -r 140 <al >/dev/audio

 .EE

 .PP

 Use with Ultima 6 M files:

 .IP

 .EX

-% opl2 -n 60 <mfile >/dev/audio

+% opl2 -r 60 <mfile >/dev/audio

 .EE

 .SH "SEE ALSO"

 .IR wl3d (1) ,

 .IR audio (3)

+.PP

+Yamaha

+``YM3812 Application Manual'',

+1994.

 .SH HISTORY

 .I Opl2

 first appeared in 9front (May, 2016), based on

--- a/opl2m.c

+++ b/opl2m.c

@@ -7,13 +7,13 @@

 void	opl2init(int);

 enum{

-	Rate = 44100,

+	OPLrate = 49716,	/* 3579545Hz master clock / 72 */

 };

 void

 usage(void)

 {

-	fprint(2, "usage: %s [-n nsamp] [file]\n", argv0);

+	fprint(2, "usage: %s [-r rate] [file]\n", argv0);

 	exits("usage");

 }

@@ -20,15 +20,18 @@

 void

 main(int argc, char **argv)

 {

-	int r, v, dt, nsamp, fd;

-	uchar *sb, u[4];

-	Biobuf *bi, *bo;

+	int rate, n, r, v, fd, pfd[2];

+	uchar sb[65536 * 4], u[4];

+	double f, dt;

+	Biobuf *bi;

 	fd = 0;

-	nsamp = Rate / 700;

+	rate = OPLrate;

 	ARGBEGIN{

-	case 'n':

-		nsamp = Rate / atoi(EARGF(usage()));

+	case 'r':

+		rate = atoi(EARGF(usage()));

+		if(rate <= 0 || rate > OPLrate)

+			usage();

 		break;

 	default:

 		usage();

@@ -37,21 +40,41 @@

 		if((fd = open(*argv, OREAD)) < 0)

 			sysfatal("open: %r");

 	bi = Bfdopen(fd, OREAD);

-	bo = Bfdopen(1, OWRITE);

-	if(bi == nil || bo == nil)

+	if(bi == nil)

 		sysfatal("Bfdopen: %r");

-	nsamp *= 4;

-	if((sb = malloc(nsamp)) == nil)

-		sysfatal("malloc: %r");

-	opl2init(Rate);

-	while(Bread(bi, u, sizeof u) > 0){

+	opl2init(OPLrate);

+	if(pipe(pfd) < 0)

+		sysfatal("pipe: %r");

+	switch(rfork(RFPROC|RFFDG)){

+	case -1:

+		sysfatal("rfork: %r");

+	case 0:

+		close(0);

+		close(pfd[1]);

+		dup(pfd[0], 0);

+		execl("/bin/audio/pcmconv", "pcmconv", "-i", "s16c2r49716", "-o", "s16c2r44100", nil);

+		sysfatal("execl: %r");

+	default:

+		close(1);

+		close(pfd[0]);

+	}

+	f = (double)OPLrate / rate;

+	dt = 0;

+	while((n = Bread(bi, u, sizeof u)) > 0){

 		r = u[0];

 		v = u[1];

-		dt = u[3]<<8 | u[2];

 		opl2wr(r, v);

-		while(dt-- > 0){

-			opl2out(sb, nsamp);

-			Bwrite(bo, sb, nsamp);

+		dt += (u[3] << 8 | u[2]) * f;

+		while((n = dt) > 0){

+			if(n > sizeof sb / 4)

+				n = sizeof sb / 4;

+			dt -= n;

+			n *= 4;

+			opl2out(sb, n);

+			write(pfd[1], sb, n);

 		}

 	}

+	if(n < 0)

+		sysfatal("read: %r");

+	exits(nil);

 }