usrp1: Fail in case of unsupported configuration

There might be some configuration that's not supported by osmo-bts-usrp1,
and we should reject that properly.

Change-Id: Ic7308ce0c57439fe97668bd31801c4bf76b797ad
Closes: OS#3348
diff --git a/Transceiver52M/device/usrp1/USRPDevice.cpp b/Transceiver52M/device/usrp1/USRPDevice.cpp
index 7a31c97..5705e22 100644
--- a/Transceiver52M/device/usrp1/USRPDevice.cpp
+++ b/Transceiver52M/device/usrp1/USRPDevice.cpp
@@ -655,5 +655,17 @@
 			       const std::vector<std::string>& tx_paths,
 			       const std::vector<std::string>& rx_paths)
 {
+	if (tx_sps != rx_sps) {
+		LOG(ERROR) << "USRP1 requires tx_sps == rx_sps";
+		return NULL;
+	}
+	if (chans != 1) {
+		LOG(ERROR) << "USRP1 supports only 1 channel";
+		return NULL;
+	}
+	if (lo_offset != 0.0) {
+		LOG(ERROR) << "USRP1 doesn't support lo_offset";
+		return NULL;
+	}
 	return new USRPDevice(tx_sps, rx_sps, iface, chans, lo_offset, tx_paths, rx_paths);
 }