dexter has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-bsc/+/30922 ) Change subject: abis_rsl: fix frame number calculation ...................................................................... abis_rsl: fix frame number calculation The formula that is used to recover the (relative) frame number from the T1, T2, T3 parameters matches the definition in the spec, but since the partial term t3-t2 can be negative special precaution is required when performing the MOD 26 operation. This is due to the modulo implementation in C/C++, which has a very specific understanding on how to deal with negative input parameters. Change-Id: I5fb2b0ada8d409730ac22963741fb4ab0026abdd Related: OS#5198 --- M src/osmo-bsc/abis_rsl.c 1 file changed, 3 insertions(+), 1 deletion(-) git pull ssh://gerrit.osmocom.org:29418/osmo-bsc refs/changes/22/30922/1 diff --git a/src/osmo-bsc/abis_rsl.c b/src/osmo-bsc/abis_rsl.c index 640ff4d..fe5cfc6 100644 --- a/src/osmo-bsc/abis_rsl.c +++ b/src/osmo-bsc/abis_rsl.c @@ -1817,10 +1817,12 @@ rqd_ta = rqd->ta; /* See also 3GPP TS 04.08, section 10.5.2.38 and 3GPP TS 08.58, section 9.3.8 */ + /* NOTE: The forumula to compute fn was slightly altered to account for the C/C++ + * specific modulo definition. */ t1 = rqd->ref.t1; t2 = rqd->ref.t2; t3 = rqd->ref.t3_low | (rqd->ref.t3_high << 3); - fn = (51 * ((t3-t2) % 26) + t3 + 51 * 26 * t1); + fn = 51 * ((((t3-t2) % 26) + 26) % 26) + t3 + 51 * 26 * t1; LOG_BTS(rqd->bts, DRSL, LOGL_INFO, "CHAN RQD: fn(t1=%u,t3=%u,t2=%u) = %u\n", t1, t3, t2, fn); } -- To view, visit https://gerrit.osmocom.org/c/osmo-bsc/+/30922 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-bsc Gerrit-Branch: master Gerrit-Change-Id: I5fb2b0ada8d409730ac22963741fb4ab0026abdd Gerrit-Change-Number: 30922 Gerrit-PatchSet: 1 Gerrit-Owner: dexter &lt;pmaier(a)sysmocom.de&gt; Gerrit-MessageType: newchange