Revert "Rewrite Packet Downlink Assignment"

This reverts commit 896574e92bea09ed8d39688b6fdf504e84521746,
I52ec9b07413daabba8cd5f1fba5c7b3af6a33389.

This commit was found (empirically) to be a regression, rendering GPRS service
fatally unreliable.

Related: OS#3013
Change-Id: Idcba0381f70eb7f7c9aefdee9dfeafd5de96a9be

1 files changed, 48 insertions, 73 deletions

diff --git a/src/encoding.cpp b/src/encoding.cpp
index 279bbfe8..7b711b81 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -44,21 +44,6 @@ extern "C" {
 #define set_H(bv) set_x(bv, H)
 
 /* { 0 | 1 < TIMING_ADVANCE_INDEX : bit (4) > } */
-static inline int write_ta_index(bitvec *dest, int8_t tai)
-{
-	int rc;
-
-	if (tai < 0) /* No TIMING_ADVANCE_INDEX: */
-		set_0(dest);
-
-	/* TIMING_ADVANCE_INDEX: */
-	set_1(dest);
-	rc = bitvec_set_u64(dest, tai, 4, false);
-	check(rc);
-
-	return 0;
-}
-
 static inline bool write_tai(bitvec *dest, unsigned& wp, int8_t tai)
 {
 	if (tai < 0) { /* No TIMING_ADVANCE_INDEX: */
@@ -174,58 +159,52 @@ static inline int write_tfi_usf(bitvec *dest, const gprs_rlcmac_ul_tbf *tbf, uin
 	return 0;
 }
 
-/* 3GPP TS 44.018 §10.5.2.16 IA Rest Octets ::= Packet Downlink Assignment */
-static inline int write_ia_rest_downlink(const gprs_rlcmac_dl_tbf *tbf, bitvec *dest,
-					 bool polling, bool ta_valid, uint32_t fn,
-					 uint8_t alpha, uint8_t gamma, int8_t ta_idx)
+static int write_ia_rest_downlink(
+	gprs_rlcmac_dl_tbf *tbf,
+	bitvec * dest, unsigned& wp,
+	uint8_t polling, bool ta_valid, uint32_t fn,
+	uint8_t alpha, uint8_t gamma, int8_t ta_idx)
 {
-	int rc;
-
-	set_H(dest); set_H(dest);
-	set_0(dest); set_1(dest); /* 00 Packet Downlink Assignment */
-
-	rc = bitvec_set_u64(dest, tbf->tlli(), 32, false); /* TLLI */
-	check(rc);
-
-	set_1(dest);
-	rc = bitvec_set_u64(dest, tbf->tfi(), 5, false);   /* TFI_ASSIGNMENT */
-	check(rc);
-
-	/* RLC acknowledged mode */
-	set_0(dest); /* RLC_MODE */
-
-	rc = write_alpha_gamma(dest, alpha, gamma);        /* ALPHA and GAMMA */
-	check(rc);
-
-	rc = bitvec_set_bit(dest, (bit_value)polling); /* POLLING */
-	check(rc);
-
-	/* N. B: NOT related to TAI! */
-	rc = bitvec_set_bit(dest, (bit_value)ta_valid); /* TA_VALID */
-	check(rc);
-
-	rc = write_ta_index(dest, ta_idx);
-	check(rc);
-
+	if (!tbf) {
+		LOGP(DRLCMACDL, LOGL_ERROR,
+			"Cannot encode DL IMMEDIATE ASSIGNMENT without TBF\n");
+		return -EINVAL;
+	}
+	// GSM 04.08 10.5.2.16 IA Rest Octets
+	bitvec_write_field(dest, &wp, 3, 2);   // "HH"
+	bitvec_write_field(dest, &wp, 1, 2);   // "01" Packet Downlink Assignment
+	bitvec_write_field(dest, &wp,tbf->tlli(),32); // TLLI
+	bitvec_write_field(dest, &wp,0x1,1);   // switch TFI   : on
+	bitvec_write_field(dest, &wp,tbf->tfi(),5);   // TFI
+	bitvec_write_field(dest, &wp,0x0,1);   // RLC acknowledged mode
+	if (alpha) {
+		bitvec_write_field(dest, &wp,0x1,1);   // ALPHA = present
+		bitvec_write_field(dest, &wp,alpha,4);   // ALPHA
+	} else {
+		bitvec_write_field(dest, &wp,0x0,1);   // ALPHA = not present
+	}
+	bitvec_write_field(dest, &wp,gamma,5);   // GAMMA power control parameter
+	bitvec_write_field(dest, &wp,polling,1);   // Polling Bit
+	bitvec_write_field(dest, &wp, ta_valid, 1); // N. B: NOT related to TAI!
+	write_tai(dest, wp, ta_idx);
 	if (polling) {
-		set_1(dest);
-		rc = write_tbf_start_time(dest, fn);	/* TBF_STARTING_TIME */
-		check(rc);
-	} else
-		set_0(dest);	                     /* No TBF_STARTING_TIME */
-
-	set_0(dest); /* No P0 nor PR_MODE */
-
+		bitvec_write_field(dest, &wp,0x1,1);   // TBF Starting TIME present
+		bitvec_write_field(dest, &wp,(fn / (26 * 51)) % 32,5); // T1'
+		bitvec_write_field(dest, &wp,fn % 51,6);               // T3
+		bitvec_write_field(dest, &wp,fn % 26,5);               // T2
+	} else {
+		bitvec_write_field(dest, &wp,0x0,1);   // TBF Starting TIME present
+	}
+	bitvec_write_field(dest, &wp,0x0,1);   // P0 not present
+	//		bitvec_write_field(dest, &wp,0x1,1);   // P0 not present
+	//		bitvec_write_field(dest, &wp,,0xb,4);
 	if (tbf->is_egprs_enabled()) {
-		set_H(dest);
-		rc = bitvec_set_u64(dest, enc_ws(tbf->window_size()), 5, false); /* EGPRS Window Size */
-		check(rc);
-
-		/* The mobile station shall not report measurements: (see 3GPP TS 44.060 Table 11.2.7.1) */
-		set_0(dest); set_0(dest); /* LINK_QUALITY_MEASUREMENT_MODE */
-		set_1(dest);              /* No BEP_PERIOD2 */
-	} else
-		set_L(dest);              /* No Additions for Rel-6 */
+		/* see GMS 44.018, 10.5.2.16 */
+		bitvec_write_field(dest, &wp, 1, 1);  // "H"
+		write_ws(dest, &wp, tbf->window_size()); // EGPRS Window Size
+		bitvec_write_field(dest, &wp, 0x0, 2);    // LINK_QUALITY_MEASUREMENT_MODE
+		bitvec_write_field(dest, &wp, 0, 1);      // BEP_PERIOD2 not present
+	}
 
 	return 0;
 }
@@ -481,15 +460,11 @@ int Encoding::write_immediate_assignment(
 
 	plen = wp / 8;
 
-	if (downlink) {
-		if (!as_dl_tbf(tbf)) {
-			LOGP(DRLCMACDL, LOGL_ERROR, "Cannot encode DL IMMEDIATE ASSIGNMENT without TBF\n");
-			return -EINVAL;
-		}
-		dest->cur_bit = wp;
-		rc = write_ia_rest_downlink(as_dl_tbf(tbf), dest, polling, gsm48_ta_is_valid(ta), fn,
-					    alpha, gamma, ta_idx);
-	} else if (((burst_type == GSM_L1_BURST_TYPE_ACCESS_1) ||
+	if (downlink)
+		rc = write_ia_rest_downlink(as_dl_tbf(tbf), dest, wp,
+					    polling, gsm48_ta_is_valid(ta), fn,
+			alpha, gamma, ta_idx);
+	else if (((burst_type == GSM_L1_BURST_TYPE_ACCESS_1) ||
 		  (burst_type == GSM_L1_BURST_TYPE_ACCESS_2))) {
 		dest->cur_bit = wp;
 		rc = write_ia_rest_egprs_uplink(as_ul_tbf(tbf), dest, usf, fn, alpha, gamma, ta_idx, burst_type, ra);