Add SR_CONF key for data source

hwdriver.c

@@ -95,6 +95,8 @@ static struct sr_config_info sr_config_info_data[] = {
 		"Sound pressure level measurement range", NULL},
 	{SR_CONF_POWER_OFF, SR_T_BOOL, "power_off",
 		"Power off", NULL},
+	{SR_CONF_DATA_SOURCE, SR_T_CHAR, "data_source",
+		"Data source", NULL},
 	{0, 0, NULL, NULL, NULL},
 };
 

libsigrok.h

@@ -704,6 +704,18 @@ enum {
 	/** Power off the device. */
 	SR_CONF_POWER_OFF,
 
+	/** Data source for acquisition. If not present, acquisition from
+	 * the device is always "live", i.e. acquisition starts when the
+	 * frontend asks and the results are sent out as soon as possible.
+	 *
+	 * If present, it indicates that either the device has no live
+	 * acquisition capability (for example a pure data logger), or
+	 * there is a choice. sr_config_list() returns those choices.
+	 *
+	 * In any case if a device has live acquisition capabilities, it
+	 * is always the default. */
+	SR_CONF_DATA_SOURCE,
+
 	/*--- Acquisition modes ---------------------------------------------*/
 
 	/**