transceiver: workaround for transmit testing with no clock reset

Non-functional clock reset causes huge initial timing offset
between expected and received timestamps. Receive an initial
packet to 'set' the expected starting timestamp value for
both transmit and receive.

Signed-off-by: Thomas Tsou <ttsou@vt.edu>

2 files changed, 17 insertions, 4 deletions

diff --git a/Transceiver52M/UHDDevice.cpp b/Transceiver52M/UHDDevice.cpp
index a065ed7..c725696 100644
--- a/Transceiver52M/UHDDevice.cpp
+++ b/Transceiver52M/UHDDevice.cpp
@@ -58,6 +58,8 @@ const double rx_smpl_offset = .00005;
 const double rx_smpl_offset = .0000869;
 #endif
 
+static TIMESTAMP init_rd_ts = 0;
+
 /** Timestamp conversion
     @param timestamp a UHD or OpenBTS timestamp
     @param rate sample rate
@@ -169,8 +171,8 @@ public:
 	bool setTxFreq(double wFreq);
 	bool setRxFreq(double wFreq);
 
-	inline TIMESTAMP initialWriteTimestamp() { return 0; }
-	inline TIMESTAMP initialReadTimestamp() { return 0; }
+	inline TIMESTAMP initialWriteTimestamp() { return init_rd_ts; }
+	inline TIMESTAMP initialReadTimestamp() { return init_rd_ts; }
 
 	inline double fullScaleInputValue() { return 32000 * tx_ampl; }
 	inline double fullScaleOutputValue() { return 32000; }
@@ -546,6 +548,17 @@ void uhd_device::restart(uhd::time_spec_t ts)
 	cmd = uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS;
 	cmd.stream_now = true;
 	usrp_dev->issue_stream_cmd(cmd);
+
+	uhd::rx_metadata_t md;
+	uint32_t buff[rx_spp];
+
+	usrp_dev->get_device()->recv(buff,
+				     rx_spp,
+				     md,
+				     uhd::io_type_t::COMPLEX_INT16,
+				     uhd::device::RECV_MODE_ONE_PACKET);
+
+	init_rd_ts = convert_time(md.time_spec, actual_smpl_rt);
 }
 
 bool uhd_device::start()
@@ -912,7 +925,7 @@ ssize_t smpl_buf::read(void *buf, size_t len, TIMESTAMP timestamp)
 		num_smpls = len;
 
 	// Starting index
-	size_t read_start = data_start + (timestamp - time_start);
+	size_t read_start = data_start + (timestamp - time_start) % buf_len;
 
 	// Read it
 	if (read_start + num_smpls < buf_len) {
diff --git a/Transceiver52M/radioInterface.cpp b/Transceiver52M/radioInterface.cpp
index b733d0e..f01b528 100644
--- a/Transceiver52M/radioInterface.cpp
+++ b/Transceiver52M/radioInterface.cpp
@@ -120,9 +120,9 @@ void RadioInterface::start()
   LOG(INFO) << "starting radio interface...";
   mAlignRadioServiceLoopThread.start((void * (*)(void*))AlignRadioServiceLoopAdapter,
                                      (void*)this);
+  mRadio->start(); 
   writeTimestamp = mRadio->initialWriteTimestamp();
   readTimestamp = mRadio->initialReadTimestamp();
-  mRadio->start(); 
   LOG(DEBUG) << "Radio started";
   mRadio->updateAlignment(writeTimestamp-10000); 
   mRadio->updateAlignment(writeTimestamp-10000);