csd_v110: handle TCH/F14.4

Thanks to the work done by Mychaela (see the related Change-IDs), we
can finally implement handling of TCH/F14.4 (both T and NT modes) for
osmo-bts-trx and osmo-bts-virtual.

This channel mode is special in a way that it employs a different
rate adaptation function RAA' (defined in 3GPP TS 48.020 chapter 11),
which converts between between 290-bit blocks used on Um and Abis-E1
interfaces (E-TRAU frames on the latter) and A-TRAU frames spoken
over the A interface.

The result of function RAA' in the Uplink direction is 320 bits,
which is equal to 4 x 80-bit V.110 frames, but actually carrying
8 x 36-bit packed frames.  These 320 bits are then fed to the RA2
function, like we do for other CSD channel modes.

Change-Id: I3c3bef0bd2f72b8381597b5699e2060165b702a0
Depends: libosmo-abis.git I11fc1529f5be88fa778c7e05cb11eef58a389d40
Depends: libosmo-abis.git I1347a25ce97d5022502ee9112caded66315b09a4
Related: OS#6167

TODO-RELEASE

@@ -8,3 +8,4 @@
 # If any interfaces have been removed or changed since the last public release: c:r:0.
 #library	what			description / commit summary line
 libosmotrau	>1.6.0			osmo_csd_ra2_{16k,8k}_{pack,unpack}() API
+libosmotrau	>1.6.0			osmo_csd144_{to,from}_atrau_bits() API

src/common/bts.c

@@ -896,8 +896,8 @@ static bool bts_supports_cm_data(const struct gsm_bts *bts,
 	switch (bts->variant) {
 	case BTS_OSMO_TRX:
 		switch (cm->chan_rate) {
-		/* TODO: RSL_CMOD_CSD_NT_14k5 */
+		case RSL_CMOD_CSD_NT_14k5:
-		/* TODO: RSL_CMOD_CSD_T_14k4 */
+		case RSL_CMOD_CSD_T_14k4:
 		case RSL_CMOD_CSD_NT_12k0:
 		case RSL_CMOD_CSD_T_9k6:
 			if (cm->chan_rt != RSL_CMOD_CRT_TCH_Bm)

src/common/csd_v110.c

@@ -30,13 +30,13 @@
 #include <osmocom/gsm/protocol/gsm_04_08.h>
 #include <osmocom/isdn/v110.h>
 #include <osmocom/trau/csd_ra2.h>
+#include <osmocom/trau/csd_raa_prime.h>
 
 #include <osmo-bts/csd_v110.h>
 #include <osmo-bts/lchan.h>
 
 /* key is enum gsm48_chan_mode, so assuming a value in range 0..255 */
 const struct csd_v110_lchan_desc csd_v110_lchan_desc[256] = {
-#if 0
 	[GSM48_CMODE_DATA_14k5] = {
 		/* TCH/F14.4: 8 * 36 + 2 bits every 20 ms (14.5 kbit/s) */
 		.num_frames = 8,
@@ -44,7 +44,6 @@ const struct csd_v110_lchan_desc csd_v110_lchan_desc[256] = {
 		.num_other_bits = 2,	/* M-bits */
 		.ra2_ir = 16,
 	},
-#endif
 	[GSM48_CMODE_DATA_12k0] = {
 		/* TCH/F9.6: 4 * 60 bits every 20 ms (12.0 kbit/s) */
 		.num_frames = 4,
@@ -92,6 +91,32 @@ int csd_v110_rtp_encode(const struct gsm_lchan *lchan, uint8_t *rtp,
 	if (OSMO_UNLIKELY(desc->num_frames == 0))
 		return -ENOTSUP;
 
+	/* TCH/F14.4 is special: RAA' function is employed */
+	if (lchan->tch_mode == GSM48_CMODE_DATA_14k5) {
+		/* 3GPP TS 44.021, section 10.3 "TCH/F14.4 channel coding"
+		 * 3GPP TS 48.020, chapter 11 "THE RAA' FUNCTION" */
+		const ubit_t *m_bits = &data[0]; /* M-bits */
+		const ubit_t *d_bits = &data[2]; /* D-bits */
+		ubit_t c4, c5;
+
+		/* 3GPP TS 48.020, Table 3
+		 * | C4 | Date Rate |
+		 * | =1 | 14,4 kbit/s |
+		 * | =0 | 14.4 kbit/s idle (IWF to BSS only) | */
+		c4 = 1;
+		/* 3GPP TS 48.020, Table 4
+		 * | C5 | BSS to IWF FT | IWF to BSS UFE |
+		 * | =1 | idle | framing error |
+		 * | =0 | data | no framing error | */
+		c5 = 0;
+
+		/* Unless there is a bug, it's highly unlikely */
+		OSMO_ASSERT(data_len == CSD_V110_NUM_BITS(desc));
+
+		osmo_csd144_to_atrau_bits(&ra_bits[0], m_bits, d_bits, c4, c5);
+		goto ra1_ra2;
+	}
+
 	/* handle empty/incomplete Uplink frames gracefully */
 	if (OSMO_UNLIKELY(data_len < CSD_V110_NUM_BITS(desc))) {
 		/* encode N idle frames as per 3GPP TS 44.021, section 8.1.6 */
@@ -178,6 +203,18 @@ int csd_v110_rtp_decode(const struct gsm_lchan *lchan, uint8_t *data,
 	else /* desc->ra2_ir == 8 */
 		osmo_csd_ra2_8k_unpack(&ra_bits[0], &rtp[0], RFC4040_RTP_PLEN);
 
+	/* TCH/F14.4 is special: RAA' function is employed */
+	if (lchan->tch_mode == GSM48_CMODE_DATA_14k5) {
+		/* 3GPP TS 44.021, section 10.3 "TCH/F14.4 channel coding"
+		 * 3GPP TS 48.020, chapter 11 "THE RAA' FUNCTION" */
+		ubit_t *m_bits = &data[0]; /* M-bits */
+		ubit_t *d_bits = &data[2]; /* D-bits */
+		int rc;
+
+		rc = osmo_csd144_from_atrau_bits(m_bits, d_bits, NULL, NULL, &ra_bits[0]);
+		return rc == 0 ? CSD_V110_NUM_BITS(desc) : rc;
+	}
+
 	/* RA1'/RA1: convert from an intermediate rate to radio rate */
 	for (unsigned int i = 0; i < desc->num_frames; i++) {
 		struct osmo_v110_decoded_frame df;

src/osmo-bts-trx/main.c

@@ -196,9 +196,6 @@ int bts_model_trx_init(struct gsm_bts_trx *trx)
 	trx->support.chan_modes = NM_IPAC_MASK_CHANM_SPEECH
 				| NM_IPAC_MASK_CHANM_CSD_NT
 				| NM_IPAC_MASK_CHANM_CSD_T;
-	/* TODO: missing rate adaptation for TCH/F14.4 (see OS#6167) */
-	trx->support.chan_modes &= ~NM_IPAC_F_CHANM_CSD_T_14k4;
-	trx->support.chan_modes &= ~NM_IPAC_F_CHANM_CSD_NT_14k4;
 
 	/* The nominal value for each TRX is later overwritten through VTY cmd
 	 * 'nominal-tx-power' if present, otherwise through TRXC cmd NOMTXPOWER.

src/osmo-bts-virtual/main.c

@@ -99,9 +99,6 @@ int bts_model_trx_init(struct gsm_bts_trx *trx)
 	trx->support.chan_modes = NM_IPAC_MASK_CHANM_SPEECH
 				| NM_IPAC_MASK_CHANM_CSD_NT
 				| NM_IPAC_MASK_CHANM_CSD_T;
-	/* TODO: missing rate adaptation for TCH/F14.4 (see OS#6167) */
-	trx->support.chan_modes &= ~NM_IPAC_F_CHANM_CSD_T_14k4;
-	trx->support.chan_modes &= ~NM_IPAC_F_CHANM_CSD_NT_14k4;
 
 	return 0;
 }

tests/csd/csd_test.c

@@ -145,6 +145,10 @@ static void exec_test_case(const struct test_case *tc)
 			i, data_dec[i], data_enc[i]);
 	}
 
+	/* for TCH/F14.4, we always expect a valid block */
+	if (tc->tch_mode == GSM48_CMODE_DATA_14k5)
+		return;
+
 	fprintf(stderr, "[i] Testing '%s' (IDLE)\n", tc->name);
 
 	/* encode an idle RTP frame and print it */

tests/csd/csd_test.err

@@ -1,4 +1,16 @@
-[i] Skipping 'TCH/F14.4' (not implemented)
+[i] Testing 'TCH/F14.4' (bitnum=290)
+[i] csd_v110_rtp_encode() returns 160
+    3f 3f 3f 3f 3f 3f 3f 3f bf ff bf 7f bf bf bf bf 
+    bf bf bf bf bf bf bf bf bf bf bf bf bf bf ff 7f 
+    7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 
+    7f bf bf bf bf bf bf bf bf bf bf bf bf bf bf bf 
+    bf bf bf ff 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 
+    7f 7f 7f 7f 7f 7f bf bf bf bf bf bf bf bf bf bf 
+    bf bf bf bf bf bf bf bf ff 7f 7f 7f 7f 7f 7f 7f 
+    7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f bf bf bf bf bf 
+    bf bf bf bf bf bf bf bf bf bf bf bf bf ff 7f 7f 
+    7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 7f 
+[i] csd_v110_rtp_decode() returns 290
 [i] Testing 'TCH/F9.6' (bitnum=240)
 [i] csd_v110_rtp_encode() returns 160
     3f 3f 3f 3f bf bf bf bf ff 7f 7f 7f bf bf bf bf