tempest has uploaded this change for review. ( 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(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. Also 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 & 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(-)

git pull ssh://gerrit.osmocom.org:29418/osmo-trx refs/changes/31/41231/1

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);