Change in osmo-bts[master]: l1sap: fix gsmtap_ph_rach(): properly pack 8-bit and 11-bit RA

[laforge]

laforge has submitted this change. ( https://gerrit.osmocom.org/c/osmo-bts/+/17653 )

Change subject: l1sap: fix gsmtap_ph_rach(): properly pack 8-bit and 11-bit RA
......................................................................

l1sap: fix gsmtap_ph_rach(): properly pack 8-bit and 11-bit RA

According to 3GPP TS 44.004, section 7.4a, two alternative RACH
block formats are specified: 8 bit (1 octet) and 11 bit. The
bit order is little-endian (right to left).

In L1SAP PH-RACH.ind structure (see ph_rach_ind_param) we use
a field of type uint16_t to store RA values regardles of the
block format. Thus when packing it to bytes, we cannot just
cast uint16_t* to uint8_t*, we need to do some bit shifting.

Change-Id: I0e91d825bb2e1897647dd5403c311d833a89ff2e
---
M src/common/l1sap.c
1 file changed, 12 insertions(+), 2 deletions(-)

Approvals:
  Jenkins Builder: Verified
  laforge: Looks good to me, approved



diff --git a/src/common/l1sap.c b/src/common/l1sap.c
index 673430d..99aa11b 100644
--- a/src/common/l1sap.c
+++ b/src/common/l1sap.c
@@ -434,6 +434,7 @@
 	uint8_t *tn, uint8_t *ss, uint32_t *fn, uint8_t **data, unsigned int *len)
 {
 	uint8_t chan_nr = l1sap->u.rach_ind.chan_nr;
+	static uint8_t ra_buf[2];
 
 	*chan_type = GSMTAP_CHANNEL_RACH;
 	*fn = l1sap->u.rach_ind.fn;
@@ -454,8 +455,17 @@
 		}
 	}
 
-	*data = (uint8_t *)&l1sap->u.rach_ind.ra;
-	*len = (l1sap->u.rach_ind.is_11bit) ? 2 : 1;
+	if (l1sap->u.rach_ind.is_11bit) {
+		/* Pack as described in 3GPP TS 44.004, figure 7.4a.b */
+		ra_buf[0] = (uint8_t) (l1sap->u.rach_ind.ra >> 3);
+		ra_buf[1] = (uint8_t) (l1sap->u.rach_ind.ra & 0x07);
+		*len  = sizeof(ra_buf);
+		*data = ra_buf;
+	} else {
+		ra_buf[0] = (uint8_t) (l1sap->u.rach_ind.ra & 0xff);
+		*len  = sizeof(ra_buf[0]);
+		*data = ra_buf;
+	}
 
 	return 0;
 }

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Gerrit-Project: osmo-bts
Gerrit-Branch: master
Gerrit-Change-Id: I0e91d825bb2e1897647dd5403c311d833a89ff2e
Gerrit-Change-Number: 17653
Gerrit-PatchSet: 2
Gerrit-Owner: fixeria <axilirator at gmail.com>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: fixeria <axilirator at gmail.com>
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-MessageType: merged
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