MT#55283 add T.38 fill-in

This triggers an initial "no carrier" indication if the sender is slow
to start PCM.

Change-Id: I3513efafae06f992b3c9abd58b8ec797320c3b56
(cherry picked from commit dafb68ef80)
(cherry picked from commit e1951aa8e6)

daemon/t38.c

@@ -271,6 +271,7 @@ static bool t38_pcm_player(struct media_player *mp) {
 	int16_t smp[80];
 	int num = t38_gateway_tx(tg->gw, smp, 80);
 	if (num <= 0) {
+		ilog(LOG_DEBUG, "No T.38 PCM samples generated");
 		// use a fixed interval of 10 ms
 		timeval_add_usec(&mp->next_run, 10000);
 		timerthread_obj_schedule_abs(&mp->tt_obj, &mp->next_run);
@@ -286,6 +287,12 @@ static bool t38_pcm_player(struct media_player *mp) {
 	unsigned long long pts = tg->pts;
 	tg->pts += num;
 
+	// handle fill-in
+	if (timeval_diff(&rtpe_now, &tg->last_rx_ts) > 30000) {
+		ilog(LOG_DEBUG, "Adding T.38 fill-in samples");
+		t38_gateway_rx_fillin(tg->gw, 80);
+	}
+
 	mutex_unlock(&tg->lock);
 
 	// this reschedules our player as well
@@ -517,6 +524,8 @@ int t38_gateway_input_samples(struct t38_gateway *tg, int16_t amp[], int len) {
 		ilog(LOG_WARN | LOG_FLAG_LIMIT, "%i PCM samples were not processed by the T.38 gateway",
 				left);
 
+	tg->last_rx_ts = rtpe_now;
+
 	mutex_unlock(&tg->lock);
 
 	return 0;

include/t38.h

@@ -64,6 +64,9 @@ struct t38_gateway {
 	// player for PCM data
 	struct media_player *pcm_player;
 	unsigned long long pts;
+
+	// to handle PCM fill-in
+	struct timeval last_rx_ts;
 };
 
 void t38_init(void);