diff --git a/doc/PROTOCOL b/doc/PROTOCOL
index 64173c7..0eed887 100644
--- a/doc/PROTOCOL
+++ b/doc/PROTOCOL
@@ -70,4 +70,4 @@ Where each sample is
        4    2	Absolute time of Y sample, lower 16 bits
        6    2	Y sample (0-1023)
 
-Byte order TBD. (Defined by avr-gcc)
+Byte order is little-endian.
diff --git a/fw/accel.c b/fw/accel.c
index 5370260..1f45d66 100644
--- a/fw/accel.c
+++ b/fw/accel.c
@@ -38,11 +38,15 @@ static inline void admux(bool x)
 
 static inline void adcsra(bool start)
 {
+	/*
+	 * The ADC needs to run at clkADC <= 200 kHz for full resolution.
+	 * At clkADC = 125 kHz, a conversion takes about 110 us.
+	 */
 	ADCSRA =
 	    1 << ADEN |		/* enable ADC */
 	    (start ? 1 << ADSC : 0) |
 	    1 << ADIE |		/* enable ADC interrupts */
-	    7;			/* clkADC = clk/128 -> 62.5 kHz */
+	    6;			/* clkADC = clk/64 -> 126 kHz */
 }
 
 
@@ -54,8 +58,18 @@ ISR(ADC_vect)
 	if (sample)
 		sample(chan_x, v);
 
-	chan_x = !chan_x;
-	admux(chan_x);
+	if (chan_x) {
+		chan_x = 0;
+		admux(0);
+		adcsra(1);
+	}
+}
+
+
+ISR(TIMER0_OVF_vect)
+{
+	chan_x = 1;
+	admux(1);
 	adcsra(1);
 }
 
@@ -63,6 +77,15 @@ ISR(ADC_vect)
 void accel_start(void)
 {
 	adcsra(0);
-	admux(1);
-	chan_x = 1;
+
+	TCNT0 = 0;
+	OCR0A = 125;		/* 8 MHz/64/125 = 1 kHz */
+	TCCR0A =
+	    1 << WGM01 |	/* WG Mode 7 (Fast PWM to OCR0A) */
+	    1 << WGM00;
+	TCCR0B =
+	    1 << WGM02 |	/* WG Mode 7, continued */
+	    1 << CS01 |		/* clkIO/64 */
+	    1 << CS00;
+	TIMSK0 = 1 << TOIE0;	/* interrupt on overflow */
 }
diff --git a/fw/sample.c b/fw/sample.c
index 7098f78..4b1fcdf 100644
--- a/fw/sample.c
+++ b/fw/sample.c
@@ -23,31 +23,37 @@
 #include "proto.h"
 #include "dispatch.h"
 
+#include "io.h"
 
-#define	MAX_PACKET	120	/* <- MAX_PSDU -3 (hdr) -2 (CRC) */
+/* @@@ keep it small for now - we're running out of RAM :-( */
+//#define	MAX_PACKET	120	/* <- MAX_PSDU -3 (hdr) -2 (CRC) */
+#define	MAX_PACKET	50	/* <- MAX_PSDU -3 (hdr) -2 (CRC) */
 
 static uint8_t buf[MAX_PACKET+3] = { SAMPLES, 0, 0 };
 static uint16_t *p;
+static bool expect_x;
 
 
 static void handler(bool x, uint16_t v)
 {
-	bool first;
 	uint32_t t;
 
-	first = p == (uint16_t *) (buf+3);
-	if (first && !x)
+	if (x != expect_x)
 		return;
-	t = uptime();
-	if (first)
+	t = uptime_irq();
+	if (p == (uint16_t *) (buf+3))
 		*p++ = t >> 16; 
 	*p++ = t;
 	*p++ = v;
+	expect_x = !expect_x;
+
 	if (x)
 		return;
 	if ((uint8_t *) (p+4) <= buf+MAX_PACKET)
 		return;
+
 	rf_send(buf, (uint8_t *) p-buf);
+	buf[1]++;
 	p = (uint16_t *) (buf+3);
 }
 
@@ -59,6 +65,7 @@ static bool sample_first(uint8_t limit, const uint8_t *payload)
 		cli();
 		sample = handler;
 		p = (uint16_t *) (buf+3);
+		expect_x = 1;
 		sei();
 	} else {
 		cli();
diff --git a/fw/sweep.c b/fw/sweep.c
index 059c286..3aac954 100644
--- a/fw/sweep.c
+++ b/fw/sweep.c
@@ -84,6 +84,17 @@ ISR(TIMER1_OVF_vect)
 }
 
 
+uint32_t uptime_irq(void)
+{
+	uint32_t t;
+
+	t = t_up+TCNT1;
+	if (TIFR1 & TOV1)
+		t += ICR1;
+	return t;
+}
+
+
 uint32_t uptime(void)
 {
 	uint32_t a, b;
@@ -92,7 +103,8 @@ uint32_t uptime(void)
 	do {
 		cli();
 		a = t_up;
-		d = ICR1;
+		d = TCNT1;
+		cli();
 		b = t_up;
 		sei();
 	}
diff --git a/fw/sweep.h b/fw/sweep.h
index 08b325e..b0113e4 100644
--- a/fw/sweep.h
+++ b/fw/sweep.h
@@ -29,7 +29,9 @@ struct sweep {
 
 extern volatile bool sweeping;
 
+uint32_t uptime_irq(void);
 uint32_t uptime(void);
+
 void sweep_image(const struct sweep *sweep);
 void sweep_init(void);
 
diff --git a/tools/Makefile b/tools/Makefile
index c4b3802..6811779 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -15,12 +15,14 @@ MAIN = antorcha
 
 CFLAGS = -g -I../fw -I../../ben-wpan/tools/include \
 	 -I../../ben-wpan/atusb/fw/include \
-	 -Wall
-LDLIBS = -L../../ben-wpan/tools/lib -latrf -lusb
+	 -Wall \
+	 $(shell sdl-config --cflags)
+LDLIBS = -L../../ben-wpan/tools/lib -latrf -lusb \
+	 $(shell sdl-config --libs) -lSDL_gfx
 
-OBJS = antorcha.o hash.o
+OBJS = antorcha.o hash.o plot.o
 
-.PHONY:		all update ping
+.PHONY:		all update ping off
 
 all:		$(MAIN)
 
@@ -32,3 +34,6 @@ update:
 
 ping:
 		./antorcha -P
+
+off:
+		./antorcha /dev/null
diff --git a/tools/antorcha.c b/tools/antorcha.c
index d0ca4d8..f47c87c 100644
--- a/tools/antorcha.c
+++ b/tools/antorcha.c
@@ -22,9 +22,11 @@
 #include <atrf.h>
 #include <misctxrx.h>
 
-#include <hash.h>
 #include <proto.h>
 
+#include "hash.h"
+#include "plot.h"
+
 
 static int verbose = 1;
 static int debug = 0;
@@ -275,6 +277,74 @@ static void image(struct atrf_dsc *dsc, const char *name)
 }
 
 
+/* ----- Samples ----------------------------------------------------------- */
+
+
+static void samples(struct atrf_dsc *dsc)
+{
+	uint8_t buf[MAX_PSDU] = { 0, };
+	int got;
+	uint8_t *s;
+	uint16_t t_high, t_low, last;
+	int x, y;
+
+	buf[0] = 1;
+	packet(dsc, SAMPLE, 0, 0, buf, PAYLOAD);
+	plot_init();
+	while (1) {
+		got = rf_recv(dsc, buf, sizeof(buf));
+		if (got <= 3)
+			continue;
+		if (buf[0] != SAMPLES)
+			continue;
+		if (debug > 1) {
+			int i;
+
+			for (i = 0; i != got; i++)
+				fprintf(stderr, " %02x", buf[i]);
+			fprintf(stderr, "\n");
+		}
+		if (debug)
+			fprintf(stderr, "%d:", got);
+		s = buf+3;
+		t_high = *s++;
+		t_high |= *s++ << 8;
+		last = 0;
+		while (s < buf+got-2) {
+			t_low = *s++;
+			t_low |= *s++ << 8;
+			if (t_low < last)
+				t_high++;
+			last = t_low;
+			x = *s++;
+			x |= *s++ << 8;
+
+			if (debug)
+				fprintf(stderr, "\t%11.6f %d",
+				    (t_high << 16 | t_low)/1000000.0, x);
+
+			t_low = *s++;
+			t_low |= *s++ << 8;
+			if (t_low < last)
+				t_high++;
+			last = t_low;
+			y = *s++;
+			y |= *s++ << 8;
+
+			if (debug)
+				fprintf(stderr, "\t%11.6f %d\n",
+				    (t_high << 16 | t_low)/1000000.0, y);
+
+			if (!plot(x, y))
+				goto quit;
+		}
+	}
+quit:
+	buf[0] = 0;
+	packet(dsc, SAMPLE, 0, 0, buf, PAYLOAD);
+}
+
+
 /* ----- Command-line processing ------------------------------------------- */
 
 
@@ -284,7 +354,8 @@ static void usage(const char *name)
 "usage: %s [-d] image_file\n"
    "%6s %s [-d] -F firmware_file\n"
    "%6s %s [-d] -P\n"
-    , name, "", name, "", name);
+   "%6s %s [-d] -S\n"
+    , name, "", name, "", name, "", name);
 	exit(1);
 }
 
@@ -292,14 +363,14 @@ static void usage(const char *name)
 int main(int argc, char **argv)
 {
 	const char *fw = NULL;
-	int do_ping = 0;
+	int do_ping = 0, do_sample = 0;
 	struct atrf_dsc *dsc;
 	int c;
 
-	while ((c = getopt(argc, argv, "dF:P")) != EOF)
+	while ((c = getopt(argc, argv, "dF:PS")) != EOF)
 		switch (c) {
 		case 'd':
-			debug = 1;
+			debug++;
 			break;
 		case 'F':
 			fw = optarg;
@@ -307,13 +378,16 @@ int main(int argc, char **argv)
 		case 'P':
 			do_ping = 1;
 			break;
+		case 'S':
+			do_sample = 1;
+			break;
 		default:
 			usage(*argv);
 		}
 
-	if (do_ping && fw)
+	if (do_ping+do_sample+!!fw > 1)
 		usage(*argv);
-	if (do_ping || fw) {
+	if (do_ping || do_sample || fw) {
 		if (argc != optind)
 			usage(*argv);
 	} else {
@@ -328,6 +402,8 @@ int main(int argc, char **argv)
 	rf_init(dsc, 8, 15);
 	if (do_ping)
 		ping(dsc);
+	else if (do_sample)
+		samples(dsc);
 	else if (fw)
 		firmware(dsc, fw);
 	else
diff --git a/tools/plot.c b/tools/plot.c
new file mode 100644
index 0000000..bbe3d6f
--- /dev/null
+++ b/tools/plot.c
@@ -0,0 +1,130 @@
+/*
+ * tools/plot.c - Sample plot
+ *
+ * Written 2012 by Werner Almesberger
+ * Copyright 2012 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#include <stdlib.h>
+
+#include "SDL.h"
+#include "SDL_gfxPrimitives.h"
+
+#include "plot.h"
+
+
+#define XRES    1024
+#define YRES    1024
+
+#define	RADIUS	3
+
+#define	OLD_RGBA	0xffffff20
+#define	NEW_RGBA	0xffffffff
+
+
+static SDL_Surface *surf;
+static int first = 1;
+static int last_x, last_y;
+
+static SDL_Surface *back;
+static SDL_Rect back_rect = {
+	.x = 0,
+	.y = 0,
+	.w = 2*RADIUS+1,
+	.h = 2*RADIUS+1,
+};
+
+static SDL_Rect front_rect = {
+	.w = 2*RADIUS+1,
+	.h = 2*RADIUS+1,
+};
+
+
+int plot(int x, int y)
+{
+	SDL_Event event;
+
+	if (!first) {
+		SDL_BlitSurface(back, &back_rect, surf, &front_rect);
+		SDL_LockSurface(surf);
+		filledCircleColor(surf, last_x, last_y, RADIUS, OLD_RGBA);
+		SDL_UnlockSurface(surf);
+	}
+
+	front_rect.x = x;
+	front_rect.y = y;
+	x += RADIUS;
+	y += RADIUS;
+
+	SDL_BlitSurface(surf, &front_rect, back, &back_rect);
+	SDL_LockSurface(surf);
+	filledCircleColor(surf, x, y, RADIUS, NEW_RGBA);
+	SDL_UnlockSurface(surf);
+
+	if (!first)
+		SDL_UpdateRect(surf,
+		    last_x-RADIUS, last_y-RADIUS, 2*RADIUS+1, 2*RADIUS+1);
+	SDL_UpdateRect(surf, x-RADIUS, y-RADIUS, 2*RADIUS+1, 2*RADIUS+1);
+
+	first = 0;
+	last_x = x;
+	last_y = y;
+
+	while (SDL_PollEvent(&event))
+		switch (event.type) {
+		case SDL_KEYDOWN:
+			switch (event.key.keysym.sym) {
+			case SDLK_c:
+				SDL_LockSurface(surf);
+				SDL_FillRect(surf, NULL,
+				    SDL_MapRGB(surf->format, 0, 0, 0));
+				SDL_UpdateRect(surf, 0, 0, 0, 0);
+				SDL_UnlockSurface(surf);
+				break;
+			case SDLK_q:
+				return 0;
+			default:
+				break;
+			}
+			break;
+		case SDL_QUIT:
+			return 0;
+		default:
+			break;
+		}
+
+	return 1;
+}
+
+
+void plot_init(void)
+{
+	const SDL_PixelFormat *f;
+
+	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
+		fprintf(stderr, "SDL_init: %s\n", SDL_GetError());
+		exit(1);
+	}
+	atexit(SDL_Quit);
+
+	surf = SDL_SetVideoMode(XRES+2*RADIUS+1, YRES+2*RADIUS+1, 0,
+	    SDL_SWSURFACE);
+	if (!surf) {
+		fprintf(stderr, "SDL_SetVideoMode: %s\n", SDL_GetError());
+		exit(1);
+	}
+
+	f = surf->format;
+	back = SDL_CreateRGBSurface(SDL_SWSURFACE, 2*RADIUS+1, 2*RADIUS+1,
+	    f->BitsPerPixel,  f->Rmask, f->Gmask, f->Bmask, f->Amask);
+	if (!back) {
+		fprintf(stderr, "SDL_SetVideoMode: %s\n", SDL_GetError());
+		exit(1);
+	}
+}
diff --git a/tools/plot.h b/tools/plot.h
new file mode 100644
index 0000000..fb6a621
--- /dev/null
+++ b/tools/plot.h
@@ -0,0 +1,20 @@
+/*
+ * tools/plot.h - Sample plot
+ *
+ * Written 2012 by Werner Almesberger
+ * Copyright 2012 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#ifndef PLOT_H
+#define	PLOT_H
+
+int plot(int x, int y);
+void plot_init(void);
+
+#endif /* !PLOT_H */