laforge has submitted this change. (
https://gerrit.osmocom.org/c/osmo-trx/+/41231?usp=email )
Change subject: trx: Fix tx/rx-sps 4 for USRP1 devices
......................................................................
trx: Fix tx/rx-sps 4 for USRP1 devices
The existing code sets the pingOffset variable to -7231(269 - 7500)
with tx-sps = 4. The (apparent) correct value for pingOffset for
tx/rx-sps 4 is 272.
While I'm not completely sure how this patch works to fix the increased
sps value, my theory is that the original OpenBTS TRX only supported
a split sps setup(tx-sps=4, rx_sps=1 for sps=4), which created
differing decimation rates between Tx and Rx on the board.
In this case, apparently you needed to account for an advance in the
timestamp for a correct output.
With tx_sps == rx_sps, the decimation/sample rates will be the same,
and(I guess) this advance doesn't need to be accounted for.
Also changed a line in the initialization of the Rx end of the USRP
device to use the correct decimation rate when tx/rx-sps == 4.
Since osmo-trx won't allow nonequal values for tx-sps and rx-sps, I
commented out the logic that selected pingOffset based on sps.
I left it visible in the file for reference however.
Tested & working on the URAN-1, a USRP1 clone designed for GSM.
Change-Id: I3b08c23a3e7d4a226cd23b9fe42558f596a63257
---
M Transceiver52M/device/usrp1/USRPDevice.cpp
1 file changed, 8 insertions(+), 7 deletions(-)
Approvals:
laforge: Looks good to me, approved
fixeria: Looks good to me, but someone else must approve; Verified
diff --git a/Transceiver52M/device/usrp1/USRPDevice.cpp
b/Transceiver52M/device/usrp1/USRPDevice.cpp
index 63a9bcc..21cbd7e 100644
--- a/Transceiver52M/device/usrp1/USRPDevice.cpp
+++ b/Transceiver52M/device/usrp1/USRPDevice.cpp
@@ -75,18 +75,19 @@
* split sample rate Tx/Rx - 4/1 sps we need to need to
* compensate for advance rather than delay.
*/
- if (tx_sps == 1)
- pingOffset = 272;
- else if (tx_sps == 4)
- pingOffset = 269 - 7500;
- else
- pingOffset = 0;
+ pingOffset = 272;
+
+ /* Split SPS (4/1) unsupported on USRP1
+ * if(tx_sps == 4 && rx_sps == 1)
+ * pingOffset = 269 - 7500;
+ */
#ifdef SWLOOPBACK
samplePeriod = 1.0e6/actualSampleRate;
loopbackBufferSize = 0;
gettimeofday(&lastReadTime,NULL);
firstRead = false;
+ pingOffset = 0;
#endif
}
@@ -101,7 +102,7 @@
m_uRx.reset();
try {
m_uRx = usrp_standard_rx_sptr(usrp_standard_rx::make(
- 0, decimRate * tx_sps, 1, -1,
+ 0, decimRate, 1, -1,
usrp_standard_rx::FPGA_MODE_NORMAL,
1024, 16 * 8, rbf));
m_uRx->set_fpga_master_clock_freq(masterClockRate);
--
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Gerrit-MessageType: merged
Gerrit-Project: osmo-trx
Gerrit-Branch: master
Gerrit-Change-Id: I3b08c23a3e7d4a226cd23b9fe42558f596a63257
Gerrit-Change-Number: 41231
Gerrit-PatchSet: 2
Gerrit-Owner: tempest <[email protected]>
Gerrit-Reviewer: Hoernchen <[email protected]>
Gerrit-Reviewer: fixeria <[email protected]>
Gerrit-Reviewer: laforge <[email protected]>
Gerrit-Reviewer: tnt <[email protected]>
Gerrit-Reviewer: ttsou <[email protected]>
Gerrit-CC: pespin <[email protected]>
