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From: cinap_lenrek@felloff.net
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Subject: Re: [9front] recent kernel changes break built-in wacom serial tablet on
Reply-To: 9front@9front.org
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another possibility:

at startup, it aux/wacom asks the device for the
resolution that it will later use for scaling:

int
query(Tablet* t)
{
	uchar buf[11];

	if(write(t->ser, "&0*", 3) < 3) return -1;
	do {
		if(read(t->ser, buf, 1) < 1) return -1;
	} while(buf[0] != 0xC0);
	if(readn(t->ser, buf+1, 10) < 10) return -1;
	t->xmax = (buf[1] << 9) | (buf[2] << 2) | ((buf[6] >> 5) & 3);
	t->ymax = (buf[3] << 9) | (buf[4] << 2) | ((buf[6] >> 3) & 3);
	t->pmax = buf[5] | (buf[6] & 7);
	t->version = (buf[9] << 7) | buf[10];
	if(write(t->ser, "1", 1) < 1) return -1;
	return 0;
}

if this procress goes wrong for some reason
(because theres maybe garbage in the fifo?),
we might end up with a out-of-range t->ymax,
causing the y-corrdinate to become stuck at
eigther extreme?

adding a debug print here would be helpfull,
and maybe just calling query() multiple times
to see if the values stay consistent:

fprint(2, "query: xmax=%d ymax=%d pmax=%d version=%d\n",
	t->xmax, t->ymax, t->pmax, t->version);

...

	if(query(t) < 0) sysfatal("%r");
+	if(query(t) < 0) sysfatal("%r");
+	if(query(t) < 0) sysfatal("%r");

and finally, we should add a debug print in
readpacket() *BEFORE* the scaling:

	m->b = head & 7;
	m->x = (buf[0] << 9) | (buf[1] << 2) | ((buf[5] >> 5) & 3);
	m->y = (buf[2] << 9) | (buf[3] << 2) | ((buf[5] >> 3) & 3);
	m->p = ((buf[5] & 7) << 7) | buf[4];

fprint(2, "readpacket: b=%x x=%d y=%d p=%d\n", m->b, m->x, m->y, m->p);

...

in any case, lets make sure we understand
what is actually happening because i dont
know of any way how our recent changes could
have screwed up your tablet :(

--
cinap