tempest has uploaded this change for review. (
https://gerrit.osmocom.org/c/osmo-trx/+/41230?usp=email )
Change subject: Fix tx/rx-sps 4 for USRP1 devices
......................................................................
Fix tx/rx-sps 4 for USRP1 devices
In Transceiver52M/device/usrp1/USRPDevice.cpp, 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(as seen in the block comment on lines 72-77) OpenBTS,
where this code is adapted from, only supported a split sps setup(tx-sps=4,
rx_sps=1 for sps=4), which created a differing decimation rate 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.
However, in the case tx_sps == rx_sps, the decimation/sample rates will be the
same, and(I guess) this advance doesn't need to be accounted for. I also had to
change a line in the initialization of the Rx end of the USRP device to allow
it to have a correct decimation rate when the sps values are 4.
Furthermore, I commented out the line that would create different pingOffset
values for split sps values, since osmo-trx won't allow nonequal values for
tx-sps and rx-sps. I left it visible in the file for reference however.
Tested and working(with EDGE!) on the URAN-1, a clone of the USRP1 designed for
GSM applications.
Change-Id: Ie5263b6fd00c2bf18bd1132355aeebd9b4d9ffda
---
M Transceiver52M/device/usrp1/USRPDevice.cpp
1 file changed, 8 insertions(+), 7 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-trx refs/changes/30/41230/1
diff --git a/Transceiver52M/device/usrp1/USRPDevice.cpp
b/Transceiver52M/device/usrp1/USRPDevice.cpp
index 63a9bcc..fcd60c4 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: newchange
Gerrit-Project: osmo-trx
Gerrit-Branch: master
Gerrit-Change-Id: Ie5263b6fd00c2bf18bd1132355aeebd9b4d9ffda
Gerrit-Change-Number: 41230
Gerrit-PatchSet: 1
Gerrit-Owner: tempest <[email protected]>
