Re: [9fans] trace.c

["Skip Tavakkolian" <fst@centurytel.net>]

> (hmm, i guess the above _is_ the man page ;-)).

Also realtime(3) is not there.

BTW, I played with it when it first appeared (2002?) and couldn't
work it right, probably due to my incorrect understanding.  I
was trying to write a deterministic cat for copying CD audio files to
/dev/audio on a slow machine (K6-166Mhz).  Regular cat results in a
periodic chop, which I assumed (wild guess more like it) was buffer
underrun.

I think there was an example in the manpage too but a few more would
have been nice.

Anyhow, here is the rtcat.c which I couldn't make work. I don't remember
a thing about the details now.

------------------ rtcat.c --- DOESN'T WORK -------------
#include <u.h>
#include <libc.h>

char *	T = "10s";	/* the period between releases */
char *	D = "5s";	/* deadline before we must start (within T) */
char *	C = "1.5s";	/* time we have to do our work */
int		verbose, debug, tset, dset, cset;
char *clonedev = "#R/realtime/clone";

/*
 we've got to read /dev/volume and look for speed attribute.
 then we read the /dev/audiostat to get the buffer size for causing
 DMA. Then we use this formula to calculate the period (T) for
 this function:  Ex. 'speed 44100' would yeild:
	T = 1 ÷ (($speed × 16) ÷ ((1024 × 8))  OR 1 ÷ (($speed × 2) ÷ 1024))
	C = How long to run?
	D = T - C
*/
void
rtcat(int f, char *s)
{
	char buf[44100 * 2];		/* bytes: actually (44100×16)÷8  */
	long n;

	int fd;

	if ((fd = open(clonedev, ORDWR)) < 0)
		sysfatal("%s: %r", clonedev);
	if (fprint(fd, "T=%s D=%s C=%s  procs=%d resources= admit", T,D,C,getpid()) < 0)
		sysfatal("%s: admit: %r", clonedev);
	for (;;) {
		if ((n=read(f, buf, (long)sizeof buf))>0) {
			if(write(1, buf, n)!=n)
				sysfatal("write error copying %s: %r", s);
			if (fprint(fd, "yield") < 0)
				sysfatal("%s: yield: %r", clonedev);
		} else if(n < 0) {
			sysfatal("error reading %s: %r", s);
		} else {
			break;
		}
	}

	if (fprint(fd, "remove") < 0)
		sysfatal("%s: remove: %r", clonedev);
	close(fd);
}

static void
usage(void)
{
	fprint(2, "Usage: %s [-T period] [-D deadline] [-C cost] [-v]\n", argv0);
	exits(nil);
}

void
main(int argc, char *argv[])
{
	int f, i;

/*
	ARGBEGIN {
	case 'T':
		T = EARGF(usage());
		tset++;
		break;
	case 'D':
		D = EARGF(usage());
		dset++;
		break;
	case 'C':
		C = EARGF(usage());
		cset++;
		break;
	case 'v':
		verbose++;
		break;
	case 'd':
		debug++;
		break;
	default:
		usage();
	}
	ARGEND;
	if (tset && !dset) D = T;
*/

	argv0 = "rtcat";
	if(argc == 1)
		rtcat(0, "<stdin>");
	else for(i=1; i<argc; i++) {
		f = open(argv[i], OREAD);
		if(f < 0)
			sysfatal("can't open %s: %r", argv[i]);
		else{
			rtcat(f, argv[i]);
			close(f);
		}
	}
	exits(0);
}