diff --git a/prod/atusb b/prod/atusb
index 684b6df..6e8658f 100755
--- a/prod/atusb
+++ b/prod/atusb
@@ -24,8 +24,90 @@ led()
 
 gpio_usb()
 {
-	step "GPIO scan"
-	todo
+	# P_ON state (after reset; transceiver pull-up/downs active)
+
+#
+#		BBBBBBBB CCCCCCCC DDDDDDDD
+#		01234567 01234567 01234567
+#
+#		-xxxS-L- -x-----n InMM-S--     
+#		    T E         R RSIO C
+#
+# Pull in P_ON      v           ^ -^-v v
+#
+
+	step "GPIO scan (P_ON)"
+	cmd "$LOCAL_EXEC atrf-gpio -d $LOCAL_DUT -p \
+		HHHHoHxH.HxHxHxHh.ohzoHoHH	'# reset state (H)'	\
+		HHHH0HxH.HxHxHxHh.ohzoHoHH	'# test SLP_TR (0)'	\
+		HHHHoH0H.HxHxHxHh.ohzoHoHH	'# test LED (0)'	\
+		HHHHoHxH.HxHxHxHh.LhzoHoHH	'# test IRQ_RF (0)'	\
+		HHHHoHxH.HxHxHxHh.o0zoHoHH	'# test nSEL (0)'	\
+		HHHHoHxH.HxHxHxHh.ohz0HoHH	'# test MOSI (0)'	\
+		HHHHoHxH.HxHxHxHh.ohzoH0HH	'# test SCLK (0)'	\
+		0000o0x0.0x0x0x0h.ohzo0o00	'# reset state (0)'	\
+		000010x0.0x0x0x0h.ohzo0o00	'# test SLP_TR (1)'	\
+		0000o010.0x0x0x0h.ohzo0o00	'# test LED (1)'	\
+		0000o0x0.0x0x0x0h.o1zo0o00	'# test nSEL (1)'	\
+		0000o0x0.0x0x0x0h.ohz10o00	'# test MOSI (1)'	\
+		0000o0x0.0x0x0x0h.ohzo0100	'# test SCLK (1)'"
+	doit
+
+	# TRX_OFF state (transceiver pull-up/downs inactive)
+
+	#	-xxxS-L- -x-----n InMM-S--     
+	#	    T E         R RSIO C
+
+	step "GPIO scan (TRX_OFF)"
+	cmd "$LOCAL_EXEC atrf-gpio -d $LOCAL_DUT \
+		HHHH0HzH.HxHxHxHh.oHzHHHHH	'# TRX_OFF state (H)'	\
+		HHHH0H0H.HxHxHxHh.oHzHHHHH	'# test LED'		\
+		HHHH0HzH.HxHxHxHh.o0zHHHHH	'# test nSEL'		\
+		HHHH0HzH.HxHxHxHh.oHz0HHHH	'# test MOSI'		\
+		HHHH0HzH.HxHxHxHh.oHzHH0HH	'# test SCLK'"
+	doit
+
+	# INT
+
+	#	-xxxS-L- -x-----n InMM-S--     
+	#	    T E         R RSIO C
+
+	step "GPIO scan (INT)"
+	cmd "$LOCAL_EXEC atrf-gpio -d $LOCAL_DUT -p	\
+		xxxxxxxx.xxxxxxxx.oxxxxxxx	'# reset state'		\
+		0x04=1				'# IRQ_POLARITY = 1'	\
+		xxxxxxxx.xxxxxxxx.hxxxxxxx	'# test INT (1)'	\
+		xxxxxxxx.xxxxxxxx.h0xxxxxx	'# test INT (2)'	\
+		xxxxxxxx.xxxxxxxx.h1xxxxxx	'# restore nSEL'	\
+		0x04=0				'# IRQ_POLARITY = 0'	\
+		xxxxxxxx.xxxxxxxx.o1xxxxxx	'# test INT again'"
+	doit
+
+	# SLP_TR
+
+	#	-xxxS-L- -x-----n InMM-S--     
+	#	    T E         R RSIO C
+
+	step "GPIO scan (SLP_TR)"
+	cmd "$LOCAL_EXEC atrf-gpio -d $LOCAL_DUT			\
+		02=9 delay			'# enter PLL_ON'	\
+		02:9/0x1f			'# verify state'	\
+		frame				'# one-byte frame'	\
+		0xf:				'# clear interrupts'	\
+		0xe=8				'# enable TRX_END intr'	\
+		xxxxxxxx.xxxxxxxx.oxxxxxxx	'# confirm INT'		\
+		slp_tr delay			'# send frame'		\
+		xxxxxxxx.xxxxxxxx.hxxxxxxx	'# check INT'"
+	doit
+
+	# nRST
+
+	step "GPIO scan (nRST)"
+	cmd "$LOCAL_EXEC atrf-gpio -d $LOCAL_DUT			\
+		02:8/0x1f			'# verify TRX_OFF'	\
+		reset				'# reset transceiver'	\
+		02:0/0x1f			'# verify P_ON'"
+	doit
 }