utils: fix bmark_rate MIMO synchronization

Fix USRP2 MIMO synchronization in benchmark_rate.

When synchronizing N2XXs connected with a MIMO cable, only the master's
time needs to be set; the slave will be synchronized automatically.
Currently, calling set_time_unknown_pps will attempt to synchronize the
slave on the next PPS, which can cause problems since the MIMO cable
doesn't propogate a PPS signal.

1 files changed, 10 insertions, 9 deletions

diff --git a/host/examples/benchmark_rate.cpp b/host/examples/benchmark_rate.cpp
index 88be83a7b..3a089dc62 100644
--- a/host/examples/benchmark_rate.cpp
+++ b/host/examples/benchmark_rate.cpp
@@ -469,16 +469,17 @@ int UHD_SAFE_MAIN(int argc, char *argv[]){
     }
 
     std::cout << boost::format("[%s] Setting device timestamp to 0...") % NOW() << std::endl;
-    const bool sync_channels =
-            pps == "mimo" or
-            ref == "mimo" or
-            rx_channel_nums.size() > 1 or
-            tx_channel_nums.size() > 1
-    ;
-    if (!sync_channels) {
-       usrp->set_time_now(0.0);
+    if (pps == "mimo" or ref == "mimo") {
+        // only set the master's time, the slave's is automatically sync'd
+        usrp->set_time_now(uhd::time_spec_t(0.0), 0);
+        // ensure that the setter has completed
+        usrp->get_time_now();
+        // wait for the time to sync
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    } else if (rx_channel_nums.size() > 1 or tx_channel_nums.size() > 1) {
+        usrp->set_time_unknown_pps(uhd::time_spec_t(0.0));
     } else {
-       usrp->set_time_unknown_pps(uhd::time_spec_t(0.0));
+        usrp->set_time_now(0.0);
     }
 
     //spawn the receive test thread