From 950de61b9032247c937711ff7077e4c1a7332e0d Mon Sep 17 00:00:00 2001
From: Richard Fuchs <rfuchs@sipwise.com>
Date: Fri, 14 Mar 2025 10:04:40 -0400
Subject: [PATCH] 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 dafb68ef80000a9137a0ecc0a64693b089f37e68)
(cherry picked from commit d0c557a7dc06be11a377f4c127765f24c5f8e02d)
---
 daemon/t38.c  | 9 +++++++++
 include/t38.h | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/daemon/t38.c b/daemon/t38.c
index 2aaaf6380..99da98668 100644
--- a/daemon/t38.c
+++ b/daemon/t38.c
@@ -272,6 +272,7 @@ 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);
@@ -287,6 +288,12 @@ 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
@@ -516,6 +523,8 @@ 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;
diff --git a/include/t38.h b/include/t38.h
index cc7a3d4bd..5d3dfc07a 100644
--- a/include/t38.h
+++ b/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);