--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/abis/dl_frames.c	Tue Aug 13 21:38:55 2024 +0000
@@ -0,0 +1,70 @@
+/*
+ * In this module we generate canned TRAU-DL frames for FR and EFR,
+ * which will later be transmitted on Abis when individual subslots
+ * come alive.
+ */
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/trau/trau_frame.h>
+#include <osmocom/trau/trau_rtp.h>
+
+#include "dl_frames.h"
+
+ubit_t dl_frame_fr[DL_OUTPUT_BUFLEN];
+ubit_t dl_frame_efr[DL_OUTPUT_BUFLEN];
+
+static const uint8_t gsmfr_silence_frame[33] = {
+	0xDA, 0xA7, 0xAA, 0xA5, 0x1A,
+	0x50, 0x20, 0x38, 0xE4, 0x6D, 0xB9, 0x1B,
+	0x50, 0x20, 0x38, 0xE4, 0x6D, 0xB9, 0x1B,
+	0x50, 0x20, 0x38, 0xE4, 0x6D, 0xB9, 0x1B,
+	0x50, 0x20, 0x38, 0xE4, 0x6D, 0xB9, 0x1B,
+};
+
+static const uint8_t efr_dhf_rtp[31] = {
+	0xC0, 0x85, 0xEB, 0x49, 0x0F, 0xAA, 0xD6, 0x03,
+	0xE3, 0xA1, 0x86, 0x07, 0xB0, 0xC4, 0x2C, 0x08,
+	0x04, 0x80, 0x55, 0x80, 0x00, 0x00, 0x00, 0x00,
+	0x03, 0x6B, 0x00, 0x00, 0x00, 0x00, 0x00
+};
+
+static void gen_dl_fr(void)
+{
+	struct osmo_trau_frame tf;
+	struct osmo_trau2rtp_state st;
+	int rc;
+
+	tf.dir = OSMO_TRAU_DIR_DL;
+	st.type = OSMO_TRAU16_FT_FR;
+	rc = osmo_rtp2trau(&tf, gsmfr_silence_frame, 33, &st);
+	OSMO_ASSERT(rc == 0);
+	rc = osmo_trau_frame_encode(dl_frame_fr, DL_OUTPUT_BUFLEN, &tf);
+	OSMO_ASSERT(rc == DL_OUTPUT_LEN);
+}
+
+static void gen_dl_efr(void)
+{
+	struct osmo_trau_frame tf;
+	struct osmo_trau2rtp_state st;
+	int rc;
+
+	tf.dir = OSMO_TRAU_DIR_DL;
+	st.type = OSMO_TRAU16_FT_EFR;
+	rc = osmo_rtp2trau(&tf, efr_dhf_rtp, 31, &st);
+	OSMO_ASSERT(rc == 0);
+	rc = osmo_trau_frame_encode(dl_frame_efr, DL_OUTPUT_BUFLEN, &tf);
+	OSMO_ASSERT(rc == DL_OUTPUT_LEN);
+}
+
+void init_canned_dl_frames(void)
+{
+	gen_dl_fr();
+	gen_dl_efr();
+}