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games/snes: upsample audio to 44100 hz instead of setting audio device frequency

used to set audio device frequency thru /dev/volume tho
only ac97 driver supports this. as a quick work arround,
upsample the 32000 hz audio signal to 44100 hz (without
any interpolation).

move the sample buffer room check from audiosample() into
dspstep() so that when the buffer is full (shouldnt happen),
we wont advance dspstate so samples will not get dropped.

--- a/sys/src/games/snes/dsp.c

+++ b/sys/src/games/snes/dsp.c

@@ -42,21 +42,17 @@

 enum { RELEASE, ATTACK, DECAY, SUSTAIN };

+enum { Freq = 44100 };

 static s16int sbuf[2*2000], *sbufp;

+static int stime;

 static int fd;

 void

 audioinit(void)

 {

-	int cfd;

-	static char c[] = "speed 32000";

-

 	fd = open("/dev/audio", OWRITE);

 	if(fd < 0)

-		return;

-	cfd = open("/dev/volume", OWRITE);

-	if(cfd >= 0)

-		write(cfd, c, sizeof(c));

+		sysfatal("open: %r");

 	sbufp = sbuf;

 }

@@ -63,10 +59,13 @@

 static void

 audiosample(s16int *s)

 {

-	if(sbufp < sbuf + nelem(sbuf)){

-		*sbufp++ = s[0];

-		*sbufp++ = s[1];

-	}

+	stime -= 1<<16;

+	do {

+		sbufp[0] = s[0];

+		sbufp[1] = s[1];

+		sbufp += 2;

+		stime += (32000<<16)/Freq;

+	} while(stime < 0);

 }

 int

@@ -459,7 +458,7 @@

 void

 dspstep(void)

 {

-	if(sbufp == nil)

+	if(sbufp == nil || sbufp >= sbuf+nelem(sbuf)-2)

 		return;

 	switch(dspstate++ & 31){

 	case  0: voice(0, 5); voice(1, 2); break;