Change in osmo-bsc[master]: generate_ma_for_ts(): fix: properly encode ARFCN 0 (corner case)

[fixeria]

fixeria has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-bsc/+/19998 )


Change subject: generate_ma_for_ts(): fix: properly encode ARFCN 0 (corner case)
......................................................................

generate_ma_for_ts(): fix: properly encode ARFCN 0 (corner case)

According to 3GPP TS 44.018, table 10.5.2.21.1 "Mobile Allocation
information element", in the cell allocation frequency list the
absolute RF channel numbers are placed in increasing order, except
that ARFCN 0, if included in the set, is put in the last position.

This basically means that the last bit of the Mobile Allocation
(MSB on the wire) corresponds to ARFCN 0, if it's included in
the cell allocation frequency list, or the last channel otherwise.

Recently introduced TTCN-3 test cases uncover the following problems:

  a) ARFCN 0 is encoded twice: as MSB and LSB of the bit-mask,
  b) ARFCN 0 is encoded one bit off its expected location.

Change-Id: I264a66a1405e72940a79e9e20ad6ad8f269a7bbc
Related: SYS#4868, OS#4545
---
M src/osmo-bsc/osmo_bsc_main.c
1 file changed, 1 insertion(+), 2 deletions(-)



  git pull ssh://gerrit.osmocom.org:29418/osmo-bsc refs/changes/98/19998/1

diff --git a/src/osmo-bsc/osmo_bsc_main.c b/src/osmo-bsc/osmo_bsc_main.c
index 5aa52cf..ebae0a2 100644
--- a/src/osmo-bsc/osmo_bsc_main.c
+++ b/src/osmo-bsc/osmo_bsc_main.c
@@ -261,7 +261,7 @@
 	ts->hopping.ma_len = OSMO_BYTES_FOR_BITS(num_cell_arfcns);
 
 	n_chan = 0;
-	for (i = 0; i < 1024; i++) {
+	for (i = 1; i < 1024; i++) {
 		if (!bitvec_get_bit_pos(cell_chan, i))
 			continue;
 		/* set the corresponding bit in the MA */
@@ -275,7 +275,6 @@
 
 	/* ARFCN 0 is special: It is coded last in the bitmask */
 	if (bitvec_get_bit_pos(cell_chan, 0)) {
-		n_chan++;
 		/* set the corresponding bit in the MA */
 		bitnum = (ts->hopping.ma_len * 8) - 1 - n_chan;
 		if (bitvec_get_bit_pos(ts_arfcn, 0))

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Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-Change-Id: I264a66a1405e72940a79e9e20ad6ad8f269a7bbc
Gerrit-Change-Number: 19998
Gerrit-PatchSet: 1
Gerrit-Owner: fixeria <vyanitskiy at sysmocom.de>
Gerrit-MessageType: newchange
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