ols: Determine the right trigger point when using RLE

Due to the nature of RLE, the number of samples from the start to the
trigger point is unknown. What is known is that the hardware triggers still
records a given number of raw samples to its sample memory. When reading
and expanding these raw samples from the back (remember, OLS sends the
recording back-to-front), remember the expanded sample position from the
back and then map it back to the right position from the front once the
total number of expanded samples is known.

Author: v1ne

src/hardware/openbench-logic-sniffer/api.c

@@ -403,6 +403,7 @@ static int dev_acquisition_start(const struct sr_dev_inst *sdi)
 
 	/* Reset all operational states. */
 	devc->rle_count = 0;
+	devc->trigger_rle_at_smpl_from_end = OLS_NO_TRIGGER;
 	devc->cnt_samples = devc->raw_sample_size = 0;
 	devc->cnt_rx_bytes = devc->cnt_rx_raw_samples = 0;
 	memset(devc->raw_sample, 0, 4);

src/hardware/openbench-logic-sniffer/protocol.c

@@ -152,6 +152,7 @@ SR_PRIV struct dev_context *ols_dev_new(void)
 
 	devc = g_malloc0(sizeof(struct dev_context));
 	devc->trigger_at_smpl = OLS_NO_TRIGGER;
+	devc->trigger_rle_at_smpl_from_end = OLS_NO_TRIGGER;
 
 	return devc;
 }
@@ -434,6 +435,11 @@ SR_PRIV int ols_receive_data(int fd, int revents, void *cb_data)
 					sr_dbg("RLE count: %u.", devc->rle_count);
 					devc->raw_sample_size = 0;
 
+					if (devc->trigger_at_smpl != OLS_NO_TRIGGER
+						&& devc->trigger_rle_at_smpl_from_end == OLS_NO_TRIGGER
+						&& (unsigned int)devc->trigger_at_smpl == devc->cnt_rx_raw_samples)
+							devc->trigger_rle_at_smpl_from_end = devc->cnt_samples;
+
 					/*
 					 * Even on the rare occasion that the sampling ends with an RLE message,
 					 * the acquisition should end immediately, without any timeout.
@@ -488,6 +494,12 @@ SR_PRIV int ols_receive_data(int fd, int revents, void *cb_data)
 					new_sample_buf_size - old_size);
 			}
 
+			if (devc->capture_flags & CAPTURE_FLAG_RLE
+				&& devc->trigger_at_smpl != OLS_NO_TRIGGER
+				&& devc->trigger_rle_at_smpl_from_end == OLS_NO_TRIGGER
+				&& (unsigned int)devc->trigger_at_smpl == devc->cnt_rx_raw_samples)
+					devc->trigger_rle_at_smpl_from_end = devc->cnt_samples;
+
 			for (i = 0; i < samples_to_write; i++)
 				memcpy(devc->sample_buf + (devc->cnt_samples + i) * 4, devc->raw_sample,
 					4);
@@ -516,6 +528,17 @@ SR_PRIV int ols_receive_data(int fd, int revents, void *cb_data)
 				devc->cnt_rx_bytes, devc->cnt_rx_raw_samples,
 				devc->cnt_samples);
 
+		if (devc->capture_flags & CAPTURE_FLAG_RLE) {
+			if (devc->trigger_rle_at_smpl_from_end != OLS_NO_TRIGGER)
+				devc->trigger_at_smpl =
+					devc->cnt_samples - devc->trigger_rle_at_smpl_from_end;
+			else {
+				if (devc->trigger_at_smpl != OLS_NO_TRIGGER)
+					sr_warn("No trigger point found. Short read?");
+				devc->trigger_at_smpl = OLS_NO_TRIGGER;
+			}
+		}
+
 		/*
 		 * The OLS sends its sample buffer backwards.
 		 * Flip it back before sending it on the session bus.
@@ -620,6 +643,7 @@ SR_PRIV int ols_prepare_acquisition(const struct sr_dev_inst *sdi) {
 		(MIN(devc->max_samples / num_changroups, devc->limit_samples) + 3) / 4 * 4;
 	uint32_t readcount = devc->limit_samples / 4;
 	uint32_t delaycount;
+	int trigger_point = OLS_NO_TRIGGER;
 
 	/* Basic triggers. */
 	struct ols_basic_trigger_desc basic_trigger_desc;
@@ -636,7 +660,7 @@ SR_PRIV int ols_prepare_acquisition(const struct sr_dev_inst *sdi) {
 		RETURN_ON_ERROR(ols_send_reset(serial));
 
 		delaycount = readcount * (1 - devc->capture_ratio / 100.0);
-		devc->trigger_at_smpl = (readcount - delaycount) * 4 - 1;
+		trigger_point = (readcount - delaycount) * 4 - 1;
 		for (int i = 0; i < basic_trigger_desc.num_stages; i++) {
 			sr_dbg("Setting OLS stage %d trigger.", i);
 			RETURN_ON_ERROR(ols_set_basic_trigger_stage(&basic_trigger_desc, serial, i));
@@ -649,6 +673,15 @@ SR_PRIV int ols_prepare_acquisition(const struct sr_dev_inst *sdi) {
 		delaycount = readcount;
 	}
 
+	/*
+	 * To determine the proper trigger sample position in RLE mode, a reverse
+	 * lookup is needed while reading the samples. Set up the right trigger
+	 * point in that case or the normal trigger point for non-RLE acquisitions.
+	 */
+	devc->trigger_at_smpl = trigger_point == OLS_NO_TRIGGER ? OLS_NO_TRIGGER
+		: devc->capture_flags & CAPTURE_FLAG_RLE ?
+			(int)devc->limit_samples - trigger_point : trigger_point;
+
 	/* Samplerate. */
 	sr_dbg("Setting samplerate to %" PRIu64 "Hz (divider %u)",
 			devc->cur_samplerate, devc->cur_samplerate_divider);

src/hardware/openbench-logic-sniffer/protocol.h

@@ -112,6 +112,7 @@ struct dev_context {
 	uint64_t limit_samples;
 	uint64_t capture_ratio;
 	int trigger_at_smpl;
+	int trigger_rle_at_smpl_from_end;
 	uint16_t capture_flags;
 
 	unsigned int cnt_rx_bytes; /* number of bytes received */