diff --git a/ubb-patgen/ubb-patgen.c b/ubb-patgen/ubb-patgen.c
index 241ce4e..555761f 100644
--- a/ubb-patgen/ubb-patgen.c
+++ b/ubb-patgen/ubb-patgen.c
@@ -310,7 +310,7 @@ static void wait_shifted(const struct mmcclk *clk)
 
 
 static void mmc_buffer(const struct mmcclk *clk,
-    uint8_t first, unsigned long buf, int nibbles, uint32_t mask)
+    uint8_t first, unsigned long buf, int nibbles, uint32_t mask, int trigger)
 {
 	/*
 	 * If under control of the MMC controller, DATx tri-state until we
@@ -355,6 +355,9 @@ static void mmc_buffer(const struct mmcclk *clk,
 
 	PDFUNS = mask;
 
+	if (trigger != -1)
+		while (PIN(UBB_CLK) != trigger);
+
 	/*
 	 * Send the pattern with DMA. Note that we still have to send the first
 	 * pattern, since the static state we begin from may not have been
@@ -380,7 +383,7 @@ static void mmc_buffer(const struct mmcclk *clk,
 
 
 static void send_buffer(const struct mmcclk *clk,
-    const uint8_t *buf, int nibbles, uint32_t mask)
+    const uint8_t *buf, int nibbles, uint32_t mask, int trigger)
 {
 	unsigned long phys;
 
@@ -392,12 +395,12 @@ static void send_buffer(const struct mmcclk *clk,
 	asm("sync");	/* flush the write buffer */
 
 	phys = physmem_xlat((void *) buf);
-	mmc_buffer(clk, buf[0] >> 4, phys, nibbles, mask);
+	mmc_buffer(clk, buf[0] >> 4, phys, nibbles, mask, trigger);
 }
 
 
 static void dma_pattern(const struct mmcclk *clk,
-    const char *pattern, uint32_t mask)
+    const char *pattern, uint32_t mask, int trigger)
 {
 	const uint8_t *buf;
 	int n;
@@ -413,6 +416,11 @@ static void dma_pattern(const struct mmcclk *clk,
 		exit(1);
 	}
 
+	if (trigger != -1) {
+		PDFUNC = UBB_CLK;
+		IN(UBB_CLK);
+	}
+
 	dma_init();
 
 	/* Initial static state: the first pattern. */
@@ -422,7 +430,7 @@ static void dma_pattern(const struct mmcclk *clk,
 	PDDATS = (buf[0] >> 4) << 10;
 	PDDIRS = mask;
 
-	send_buffer(clk, buf, n, mask);
+	send_buffer(clk, buf, n, mask, trigger);
 
 	/* Final static state: the last pattern. */
 
@@ -489,14 +497,16 @@ static void usage(const char *name)
 "usage: %s\n"
 "       %s [-q] -f freq_hz\n"
 "       %s [-q] [-f freq_hz] -c [active_s]\n"
-"       %s [-q] [-f freq_hz] [-C] [-m mask] [-p] file|pattern\n\n"
+"       %s [-q] [-f freq_hz] [-C|-t 0|1] [-m mask] [-p] file|pattern\n\n"
 "  -c          output bus clock on CLK without sending a pattern\n"
 "  -C          temporarily output bus clock on CLK (for debugging)\n"
 "  -f freq_hz  set bus clock to the specified frequency (default: 1 MHz)\n"
 "  -m mask     use only the DATx lines specified in the mask (default: 0xf)\n"
 "  -p          force interpretation of argument as pattern (and not file)\n"
 "  -q          quiet. Don't pretty-print frequencies; don't report clock\n"
-"              differences.\n\n"
+"              differences.\n"
+"  -t 0|1      start pattern when trigger/CLK becomes 0 or 1 respectively\n"
+"              (default: start pattern immediately)\n\n"
 "  active_s    keep running that many seconds after setting the clock\n"
 "              (default: exit immediately but leave the clock on)\n"
 "  file        file containing the pattern\n"
@@ -522,11 +532,12 @@ int main(int argc, char **argv)
 	struct timespec active_ns;
 	int keep_clk = 1;
 	uint8_t mask = 0xf;
+	int trigger = -1;
 	char *end;
 	int c;
 	unsigned long tmp;
 
-	while ((c = getopt(argc, argv, "cCf:m:pq")) != EOF)
+	while ((c = getopt(argc, argv, "cCf:m:pqt:")) != EOF)
 		switch (c) {
 		case 'f':
 			if (!frequency(optarg, &bus_hz, &bus_rel))
@@ -554,18 +565,28 @@ int main(int argc, char **argv)
 		case 'q':
 			quiet = 1;
 			break;
+		case 't':
+			if (!strcmp(optarg, "0"))
+				trigger = 0;
+			else if (!strcmp(optarg, "1"))
+				trigger = 1;
+			else
+				usage(*argv);
+			break;
 		default:
 			usage(*argv);
 		}
 
 	if (clkout && clk_only)
 		usage(*argv);
+	if ((clkout || clk_only) && trigger != -1)
+		usage(*argv);
 
 	switch (argc-optind) {
 	case 0:
 		if (clk_only)
 			break;
-		if (clkout || force_pattern)
+		if (clkout || force_pattern || trigger != -1)
 			usage(*argv);
 
 		ubb_open(UBB_ALL);
@@ -629,14 +650,14 @@ int main(int argc, char **argv)
 	mmcclk_start(&clk);
 
 	if (pattern)
-		dma_pattern(&clk, pattern, mask << 10);
+		dma_pattern(&clk, pattern, mask << 10, trigger);
 
 	if (active_s)
 		if (nanosleep(&active_ns, NULL))
 			perror("nanosleep");
 	if (pattern) {
 		mmcclk_stop();
-		ubb_close(mask << 10);
+		ubb_close(mask << 10 | (trigger == -1 ? 0 : UBB_CLK));
 	} else if (keep_clk) {
 		ubb_close(UBB_CLK);
 	} else {