Change in osmo-pcu[master]: encoding: do not encode out of range Timing Advance values

[fixeria]

fixeria has submitted this change. ( https://gerrit.osmocom.org/c/osmo-pcu/+/19731 )

Change subject: encoding: do not encode out of range Timing Advance values
......................................................................

encoding: do not encode out of range Timing Advance values

According to 3GPP TS 44.060, section 12.12 "Packet Timing Advance",
the 'TIMING_ADVANCE_VALUE' field is optional, and takes 6 bits
if present.  This means that a value that fits in range 0..63
(inclusive) can be encoded (0b111111 == 63).

It's possible that tbf->ta() returns GSM48_TA_INVALID == 220,
so the bitvec API would encode only 6 LSBs of it:

  220 & 0b111111 == 28

Let's ensure that the 'TIMING_ADVANCE_VALUE' is present iff
tbf->ta() returns a correct (0 <= x <= 63), and absent otherwise.

Change-Id: I342288ea4ef1e218e5744e9be6a8e528d4e697fa
---
M src/encoding.cpp
1 file changed, 8 insertions(+), 3 deletions(-)

Approvals:
  laforge: Looks good to me, approved
  pespin: Looks good to me, but someone else must approve
  Jenkins Builder: Verified



diff --git a/src/encoding.cpp b/src/encoding.cpp
index 5d2434b..2025a0f 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -145,7 +145,7 @@
 /* { 0 | 1 < TIMING_ADVANCE_VALUE : bit (6) > } */
 static inline void write_ta(bitvec *dest, unsigned& wp, uint8_t ta)
 {
-	if (ta >= GSM48_TA_INVALID) /* No TIMING_ADVANCE_VALUE: */
+	if (ta > 63) /* No TIMING_ADVANCE_VALUE: */
 		bitvec_write_field(dest, &wp, 0, 1);
 	else { /* TIMING_ADVANCE_VALUE: */
 		bitvec_write_field(dest, &wp, 1, 1);
@@ -667,8 +667,13 @@
 			block->u.Packet_Downlink_Assignment.TIMESLOT_ALLOCATION |= 0x80 >> tn;   // timeslot(s)
 	}
 
-	block->u.Packet_Downlink_Assignment.Packet_Timing_Advance.Exist_TIMING_ADVANCE_VALUE = 0x1; // TIMING_ADVANCE_VALUE = on
-	block->u.Packet_Downlink_Assignment.Packet_Timing_Advance.TIMING_ADVANCE_VALUE       = tbf->ta();  // TIMING_ADVANCE_VALUE
+	if (tbf->ta() > 63) { /* { 0 | 1  < TIMING_ADVANCE_VALUE : bit (6) > } */
+		block->u.Packet_Downlink_Assignment.Packet_Timing_Advance.Exist_TIMING_ADVANCE_VALUE = 0x0; // TIMING_ADVANCE_VALUE = off
+	} else {
+		block->u.Packet_Downlink_Assignment.Packet_Timing_Advance.Exist_TIMING_ADVANCE_VALUE = 0x1; // TIMING_ADVANCE_VALUE = on
+		block->u.Packet_Downlink_Assignment.Packet_Timing_Advance.TIMING_ADVANCE_VALUE       = tbf->ta();  // TIMING_ADVANCE_VALUE
+	}
+
 	if (ta_idx < 0) {
 		block->u.Packet_Downlink_Assignment.Packet_Timing_Advance.Exist_IndexAndtimeSlot     = 0x0; // TIMING_ADVANCE_INDEX = off
 	} else {

-- 
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Gerrit-Project: osmo-pcu
Gerrit-Branch: master
Gerrit-Change-Id: I342288ea4ef1e218e5744e9be6a8e528d4e697fa
Gerrit-Change-Number: 19731
Gerrit-PatchSet: 3
Gerrit-Owner: fixeria <vyanitskiy at sysmocom.de>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: fixeria <vyanitskiy at sysmocom.de>
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-Reviewer: pespin <pespin at sysmocom.de>
Gerrit-MessageType: merged
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