diff --git a/tools/atrf-gpio/atusb.c b/tools/atrf-gpio/atusb.c
index 12d5f2b..7fb69e9 100644
--- a/tools/atrf-gpio/atusb.c
+++ b/tools/atrf-gpio/atusb.c
@@ -12,16 +12,153 @@
 
 
 #include <stdlib.h>
+#include <stdio.h>
 
+#include <usb.h>
+
+#include "atusb/ep0.h"
 #include "atrf.h"
 
 #include "atrf-gpio.h"
 
 
+#define	FROM_DEV	ATUSB_FROM_DEV(0)
+
+
+static const char *name[24] = {
+	"PB0",		"PB1/P16",	"PB2/P15",	"PB3/P14",
+	"PB4/SLP_TR",	"PB5",		"PB6/LED",	"PB7",
+	"PC0",		"PC1/P13",	"PC2",		"PC3",
+	"PC4",		"PC5",		"PC6",		"PC7/nRST_RF",
+	"PD0/IRQ_RF",	"PD1/nSS",	"PD2/MISO",	"PD3/MOSI",
+	"PD4",		"PD5/SCLK",	"PD6",		"PD7"
+};
+
+
+static struct atrf_dsc *orig_dsc;
+static uint8_t orig_data[3], orig_dir[3];
+
+
+static uint8_t gpio(struct atrf_dsc *dsc,
+    uint8_t port, uint8_t *dir, uint8_t *data, uint8_t mask)
+{
+	uint8_t buf[3];
+	int res;
+
+	res = usb_control_msg(atrf_usb_handle(dsc),
+            FROM_DEV, ATUSB_GPIO, *dir << 8 | *data, mask << 8 | port,
+	    (void *) buf, sizeof(buf), 1000);
+	if (res < 0) {
+		fprintf(stderr, "ATUSB_GPIO: %s\n", usb_strerror());
+		exit(1);
+	}
+	*data = buf[1];
+	*dir = buf[2];
+	return buf[0];
+}
+
+
+static void dump(const uint8_t *expect, const uint8_t *got,
+    const uint8_t *read)
+{
+	int i;
+
+	fprintf(stderr, "name\t\tcfg exp got\n");
+	for (i = 0; i != 24; i++) {
+		int port = i >> 3;
+		int bit = 1 << (i & 7);
+
+		fprintf(stderr, "%-16s%c   %d   %d",
+		    name[i], '?',
+		    !!(expect[port] & bit), !!(got[port] & bit));
+		if ((expect[port] ^ got[port]) & read[port] & bit)
+			fprintf(stderr, "\t***\n");
+		fputc('\n', stderr);
+	}
+}
+
+
 /* ----- Decode and apply pattern ------------------------------------------ */
 
 
+static void restore_gpios(void)
+{
+	int i;
+
+	for (i = 0; i != 3; i++)
+		gpio(orig_dsc, i+1, orig_data+i, orig_dir+i, 0xff);
+}
+
+
 void do_atusb(struct atrf_dsc *dsc, const char *pattern, const char *next)
 {
-	abort();
+	static int first = 1;
+	const char *p;
+	int i, pin = 0;
+	uint8_t data[3], dir[3], mask[3], read[3], expect[3], got[3];
+	uint8_t bit;
+	int port;
+
+	data[0] = data[1] = data[2] = 0;
+	dir[0] = dir[1] = dir[2] = 0;
+	mask[0] = mask[1] = mask[2] = 0;
+	read[0] = read[1] = read[2] = 0;
+	expect[0] = expect[1] = expect[2] = 0;
+
+	if (first) {
+		orig_dsc = dsc;
+		for (i = 0; i != 3; i++)
+			gpio(dsc, i+1, orig_data+i, orig_dir+i, 0);
+		atexit(restore_gpios);
+		first = 0;
+	}
+
+	for (p = pattern; *p; p++) {
+		bit = 1 << (pin & 7);
+		port = pin >> 3;
+		switch (*p) {
+		case '1':
+			data[port] |= bit;
+			/* fall through */
+		case '0':
+			dir[port] |= bit;
+			mask[port] |= bit;
+			break;
+		case 'H':
+			expect[port] |= bit;
+			/* fall through */
+		case 'L':
+			read[port] |= bit;
+			/* fall through */
+		case 'Z':
+			data[port] |= bit;
+			mask[port] |= bit;
+			break;
+		case 'h':
+			expect[port] |= bit;
+			/* fall through */
+		case 'l':
+			read[port] |= bit;
+			/* fall through */
+		case 'z':
+			mask[port] |= bit;
+			break;
+		case 'x':
+			pin++;
+			continue;
+		default:
+			continue;
+		}
+		pin++;
+	}
+
+	for (i = 0; i <= port; i++)
+		got[i] = gpio(dsc, i+1, data+i, dir+i, 0);
+	for (i = 0; i <= port; i++)
+		if ((got[i] & read[i]) != expect[i]) {
+			dump(expect, got, read);
+			fprintf(stderr, "at \"%s\", next \"%s\"\n", pattern,
+			    next);
+			exit(1);
+		}
 }