demo: Skip generating data when all channels in a group are disabled

The generator logic determines how many samples per group (analog and
logic) need to get produced, then keeps iterating until each group has
reached the specified count. Different groups can generate different
numbers of samples per iteration, they have their own stride.

It's essential to check whether all channels in a group are disabled, to
then completely skip the respective half of the generation loop. Without
this check, the group would be expected to generate data but it won't,
which results in an endless loop. This was observed with analog channels.

There was another issue with logic channels. Unexpected logic data was
seen in the output although neither logic channel was selected.

This commit fixes bug #923.

src/hardware/demo/api.c

@@ -457,6 +457,8 @@ static int config_list(uint32_t key, GVariant **data, const struct sr_dev_inst *
 static int dev_acquisition_start(const struct sr_dev_inst *sdi)
 {
 	struct dev_context *devc;
+	GSList *l;
+	struct sr_channel *ch;
 	GHashTableIter iter;
 	void *value;
 
@@ -466,6 +468,22 @@ static int dev_acquisition_start(const struct sr_dev_inst *sdi)
 	devc = sdi->priv;
 	devc->sent_samples = 0;
 
+	devc->enabled_logic_channels = 0;
+	devc->enabled_analog_channels = 0;
+	for (l = sdi->channels; l; l = l->next) {
+		ch = l->data;
+		if (!ch->enabled)
+			continue;
+		if (ch->type == SR_CHANNEL_ANALOG) {
+			devc->enabled_analog_channels++;
+			continue;
+		}
+		if (ch->type == SR_CHANNEL_LOGIC) {
+			devc->enabled_logic_channels++;
+			continue;
+		}
+	}
+
 	g_hash_table_iter_init(&iter, devc->ch_ag);
 	while (g_hash_table_iter_next(&iter, NULL, &value))
 		demo_generate_analog_pattern(value, devc->cur_samplerate);

src/hardware/demo/protocol.c

@@ -448,7 +448,11 @@ SR_PRIV int demo_prepare_data(int fd, int revents, void *cb_data)
 	todo_us = samples_todo * G_USEC_PER_SEC / devc->cur_samplerate;
 
 	logic_done  = devc->num_logic_channels  > 0 ? 0 : samples_todo;
+	if (!devc->enabled_logic_channels)
+		logic_done = samples_todo;
 	analog_done = devc->num_analog_channels > 0 ? 0 : samples_todo;
+	if (!devc->enabled_analog_channels)
+		analog_done = samples_todo;
 
 	while (logic_done < samples_todo || analog_done < samples_todo) {
 		/* Logic */

src/hardware/demo/protocol.h

@@ -54,6 +54,8 @@ struct dev_context {
 	GHashTable *ch_ag;
 	gboolean avg; /* True if averaging is enabled */
 	uint64_t avg_samples;
+	size_t enabled_logic_channels;
+	size_t enabled_analog_channels;
 };
 
 /* Logic patterns we can generate. */