falconia has uploaded this change for review.
trau: implement TFO frame decoding functions
TFO frames of 3GPP TS 28.062 are slightly modified TRAU-UL frames,
and thus require slightly modified encoding and decoding functions.
Adding TFO frame encoding and decoding functions to libosmotrau
will allow TFO applications (sw implementations of a TFO-capable
speech transcoder) to reuse those parts of TRAU frame encoding and
decoding that are common between regular TRAU frames and TFO.
Change-Id: Ia095598622645068d62301bc4bf7de9f68065e84
---
M include/osmocom/trau/trau_frame.h
M src/trau/trau_frame.c
2 files changed, 116 insertions(+), 0 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/libosmo-abis refs/changes/94/39494/1
diff --git a/include/osmocom/trau/trau_frame.h b/include/osmocom/trau/trau_frame.h
index 5f1d708..8bdeb73 100644
--- a/include/osmocom/trau/trau_frame.h
+++ b/include/osmocom/trau/trau_frame.h
@@ -148,4 +148,11 @@
/*! Determine the time alignment in us requested by CCU in a UL frame */
int osmo_trau_frame_dl_ta_us(const struct osmo_trau_frame *fr);
+/* TFO frames are slightly modified TRAU-UL frames, and thus require slightly
+ * modified encoding and decoding functions. */
+
+int osmo_trau_frame_decode_tfo_16k(struct osmo_trau_frame *fr, const ubit_t *bits);
+int osmo_trau_frame_decode_tfo_hr1(struct osmo_trau_frame *fr, const ubit_t *bits);
+int osmo_trau_frame_decode_tfo_amr_8k(struct osmo_trau_frame *fr, const ubit_t *bits);
+
/* }@ */
diff --git a/src/trau/trau_frame.c b/src/trau/trau_frame.c
index 21e4f00..df4404d 100644
--- a/src/trau/trau_frame.c
+++ b/src/trau/trau_frame.c
@@ -1379,6 +1379,49 @@
}
}
+/*! Decode/parse a 16k TFO frame from unpacked bits to decoded format.
+ * \param[out] fr caller-allocated output data structure
+ * \param[in] bits unpacked bits containing raw TFO frame; must be aligned
+ * \returns 0 in case of success; negative on error
+ *
+ * TFO applications that need to decode TFO frames of TS 28.062 section 5.2.1
+ * (FR/EFR) or section 5.2.2.1 (AMR_TFO_16k) should use this function instead
+ * of regular osmo_trau_frame_decode_16k() in order to get appropriately
+ * modified handling of C1..C5 frame type bits:
+ *
+ * - C5 needs to be ignored because it is EMBED bit in TFO frames;
+ * - For interoperability with other potential TFO-AMR implementations
+ * out in the world that aren't GSM AMR-FR, we need to recognize additional
+ * C1..C4 bit patterns as being AMR equivalents: see Table 5.2.2.1-2 in
+ * 3GPP TS 28.062.
+ */
+int osmo_trau_frame_decode_tfo_16k(struct osmo_trau_frame *fr, const ubit_t *bits)
+{
+ uint8_t cbits4 = get_bits(bits, 17, 4);
+ /* We don't look at bit C5 because it is EMBED bit in TFO frames */
+
+ fr->type = OSMO_TRAU_FT_NONE;
+ fr->dir = OSMO_TRAU_DIR_UL; /* TFO frames are modified TRAU-UL */
+ fr->dl_ta_usec = 0;
+
+ switch (cbits4) {
+ case TRAU_FT_FR_UP >> 1:
+ fr->type = OSMO_TRAU16_FT_FR;
+ return decode16_fr(fr, bits, fr->dir);
+ case TRAU_FT_EFR >> 1:
+ fr->type = OSMO_TRAU16_FT_EFR;
+ return decode16_fr(fr, bits, fr->dir);
+ case TRAU_FT_AMR >> 1:
+ case 0x4: /* HR_AMR */
+ case 0x6: /* UMTS_AMR_2 */
+ case 0xB: /* OHR_AMR */
+ fr->type = OSMO_TRAU16_FT_AMR;
+ return decode16_amr(fr, bits, fr->dir);
+ default:
+ return -EINVAL;
+ }
+}
+
#define TRAU8_FT_AMR_NO_SPEECH_CMI 0x10 /* 1, 0, 0, 0, 0 */
#define TRAU8_FT_AMR_NO_SPEECH_CMR 0x14 /* 1, 0, 1, 0, 0 */
#define TRAU8_FT_AMR_475_515_590 0..7
@@ -1521,4 +1564,70 @@
return -EINVAL;
}
+/*! Decode/parse an HRv1 TFO frame from unpacked bits to decoded format.
+ * \param[out] fr caller-allocated output data structure
+ * \param[in] bits 160 bits containing the lsb extracted from PCM samples;
+ * must be aligned
+ * \returns 0 in case of success; negative on error
+ *
+ * TFO applications that need to decode TFO frames of TS 28.062 section 5.3.1
+ * (GSM_HR codec) should use this function instead of regular
+ * osmo_trau_frame_decode_8k() in order to get these two behavior
+ * modifications:
+ *
+ * - The sync pattern check needs to be skipped because the sync pattern
+ * may be partially overwritten by embedded TFO messages;
+ * - C5 needs to be ignored because it is EMBED bit in TFO frames.
+ *
+ * In the case of TFO, unlike regular TRAU-UL frames on Abis/Ater, there is
+ * no need to distinguish between HRv1 and AMR-8k frames by their respective
+ * sync patterns: per TS 28.062, these two TFO frame types never occur
+ * in the same bit position in TFO-superimposed PCM speech octets.
+ * Because HRv1 is the only TFO frame type that can occur in the configuration
+ * of TS 28.062 section 5.3 (only the one lsb in each PCM speech octet is
+ * overwritten), this function skips all attempts at frame type classification:
+ * the TFO application is responsible for detecting the presence of valid
+ * TFO frames for the negotiated codec type.
+ */
+int osmo_trau_frame_decode_tfo_hr1(struct osmo_trau_frame *fr, const ubit_t *bits)
+{
+ fr->type = OSMO_TRAU8_SPEECH;
+ fr->dir = OSMO_TRAU_DIR_UL; /* TFO frames are modified TRAU-UL */
+ fr->dl_ta_usec = 0;
+ return decode8_hr(fr, bits, fr->dir);
+}
+
+/*! Decode/parse an AMR_TFO_8+8k frame from unpacked bits to decoded format.
+ * \param[out] fr caller-allocated output data structure
+ * \param[in] bits 160 bits containing the second lsb extracted from
+ * PCM samples; must be aligned
+ * \returns 0 in case of success; negative on error
+ *
+ * This function is provided for TFO applications that need to decode
+ * TFO frames of TS 28.062 section 5.2.2.2, format named AMR_TFO_8+8k.
+ * The second lsb extracted from PCM samples is the entity being decoded here.
+ * Compared to osmo_trau_frame_decode_8k(), the present function requires
+ * the direction to be TRAU-UL (as always the case in TFO) and accepts
+ * only AMR-8k frame types.
+ */
+int osmo_trau_frame_decode_tfo_amr_8k(struct osmo_trau_frame *fr, const ubit_t *bits)
+{
+ fr->type = OSMO_TRAU_FT_NONE;
+ fr->dir = OSMO_TRAU_DIR_UL; /* TFO frames are modified TRAU-UL */
+ fr->dl_ta_usec = 0;
+
+ if (is_amr_low(bits)) {
+ fr->type = OSMO_TRAU8_AMR_LOW;
+ return decode8_amr_low(fr, bits, fr->dir);
+ } else if (is_amr_67(bits)) {
+ fr->type = OSMO_TRAU8_AMR_6k7;
+ return decode8_amr_67(fr, bits, fr->dir);
+ } else if (is_amr_74(bits)) {
+ fr->type = OSMO_TRAU8_AMR_7k4;
+ return decode8_amr_74(fr, bits, fr->dir);
+ }
+
+ return -EINVAL;
+}
+
/* }@ */
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