--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ater8/out_frame.c	Fri Aug 30 19:02:42 2024 +0000
@@ -0,0 +1,80 @@
+/*
+ * Here we implement our TRAU-UL bit filling function for HRv1 8 kbit/s format.
+ *
+ * This code is based (very loosely) on trau_rtp_conv.c in libosmo-abis.
+ */
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/crc8gen.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/trau/trau_frame.h>
+#include "../libhr/tw_gsmhr.h"
+
+#include "out_frame.h"
+
+/*
+ * EFR TRAU parity (also used for HR)
+ *
+ * g(x) = x^3 + x^1 + 1
+ */
+static const struct osmo_crc8gen_code gsm0860_efr_crc3 = {
+	.bits = 3,
+	.poly = 0x3,
+	.init = 0x0,
+	.remainder = 0x7,
+};
+
+void trau_frame_from_record(const int16_t *rec, struct osmo_trau_frame *tf,
+			    bool *has_taf)
+{
+	uint8_t ts101318[GSMHR_FRAME_LEN_RPF];
+	int16_t bfi, sid;
+
+	/* payload transformation is straightforward */
+	gsmhr_pack_ts101318(rec, ts101318);
+	osmo_pbit2ubit(tf->d_bits, ts101318, 14 * 8);
+	osmo_crc8gen_set_bits(&gsm0860_efr_crc3, tf->d_bits, 44, tf->crc_bits);
+
+	/* transformation of metadata flags is the messy part */
+	bfi = rec[18];
+	sid = rec[20];
+	switch (sid) {
+	case 0:
+		if (bfi) {
+			tf->xc_bits[1] = 1;
+			tf->xc_bits[2] = 1;
+			*has_taf = true;
+		} else {
+			tf->xc_bits[1] = 0;
+			tf->xc_bits[2] = 0;
+			tf->xc_bits[3] = 0;
+			*has_taf = false;
+		}
+		break;
+	case 1:
+		tf->xc_bits[1] = 1;
+		tf->xc_bits[2] = 0;
+		*has_taf = true;
+		break;
+	case 2:
+		if (bfi) {
+			tf->xc_bits[1] = 1;
+			tf->xc_bits[2] = 0;
+			*has_taf = true;
+		} else {
+			tf->xc_bits[1] = 0;
+			tf->xc_bits[2] = 0;
+			tf->xc_bits[3] = 1;
+			*has_taf = false;
+		}
+		break;
+	default:
+		OSMO_ASSERT(0);
+	}
+	/* XC5 is always UFI */
+	tf->xc_bits[4] = rec[19];
+}