Change in osmo-pcu[master]: bts: fix send_gsmtap_rach(): properly pack 11 bit RA

[fixeria]

fixeria has submitted this change. ( https://gerrit.osmocom.org/c/osmo-pcu/+/17709 )

Change subject: bts: fix send_gsmtap_rach(): properly pack 11 bit RA
......................................................................

bts: fix send_gsmtap_rach(): properly pack 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 LSB (right to left), byte order is MSB.

In PCUIF RACH.ind structure (see gsm_pcu_if_rach_ind) 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: I08a0a908f855b0d8a002df732e02781126d27dfb
---
M src/bts.cpp
1 file changed, 14 insertions(+), 2 deletions(-)

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



diff --git a/src/bts.cpp b/src/bts.cpp
index 0482168..617cd78 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -434,9 +434,21 @@
 			   const struct rach_ind_params *rip)
 {
 	struct pcu_l1_meas meas;
+	uint8_t ra_buf[2];
+
+	/* 3GPP TS 44.004 defines 11 bit RA as follows: xxxx xxxx  .... .yyy
+	 * On the PCUIF, we get 16 bit machne dependent number (LE/BE)
+	 * Over GSMTAP we send the following:           xxxx xxxx  yyy. ....
+	 * This simplifies parsing in Wireshark using its CSN.1 codec. */
+	if (rip->is_11bit) {
+		ra_buf[0] = (uint8_t) ((rip->ra >> 3) & 0xff);
+		ra_buf[1] = (uint8_t) ((rip->ra << 5) & 0xff);
+	} else {
+		ra_buf[0] = (uint8_t) (rip->ra & 0xff);
+	}
+
 	send_gsmtap_meas(categ, true, rip->trx_nr, rip->ts_nr, channel,
-			 rfn_to_fn(rip->rfn), (uint8_t *) &rip->ra,
-			 /* TODO: properly pack 11 bit RA */
+			 rfn_to_fn(rip->rfn), ra_buf,
 			 rip->is_11bit ? 2 : 1, &meas);
 }
 

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Gerrit-Project: osmo-pcu
Gerrit-Branch: master
Gerrit-Change-Id: I08a0a908f855b0d8a002df732e02781126d27dfb
Gerrit-Change-Number: 17709
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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