SoapySDR: Allow channel selection by using the subdev device argument (#416)

Add SoapySDR argument for selecting explicit streaming channel indexes

Author: holaguz

SoapyLMS7/Streaming.cpp

@@ -106,6 +106,17 @@ SoapySDR::ArgInfoList SoapyLMS7::getStreamArgsInfo(const int direction, const si
         argInfos.push_back(info);
     }
 
+    // channel selection
+    {
+      SoapySDR::ArgInfo info;
+      info.value = "0";
+      info.key = "channel";
+      info.name = "Channel";
+      info.description = "List of channels to use, separated by spaces. Defaults to 0.";
+      info.type = SoapySDR::ArgInfo::INT;
+      argInfos.push_back(info);
+    }
+
     //align phase of Rx channels
     {
         SoapySDR::ArgInfo info;
@@ -143,8 +154,41 @@ SoapySDR::Stream *SoapyLMS7::setupStream(
     config.performanceLatency = 0.5;
     config.bufferLength = 0; //auto
 
-    //default to channel 0, if none were specified
-    const std::vector<size_t> &channelIDs = channels.empty() ? std::vector<size_t>{0} : channels;
+    std::vector<size_t> chans = {};
+
+    /* Try to use the channels passed in the `channel` device argument */
+    if (_deviceArgs.count("channel")) {
+        const std::string channelstr = _deviceArgs.at("channel");
+
+        size_t num;
+        std::stringstream ss(channelstr);
+
+        while (ss >> num) {
+            chans.push_back(num);
+        }
+
+        if (chans.empty()) {
+            SoapySDR::logf(SOAPY_SDR_ERROR, "Couldn't parse 'channels' string '%s': it should be a list of integers separated by spaces.", channelstr.c_str());
+        }
+    }
+
+    if (chans.empty()) {
+        /* If `channel` was not present, or was not a valid string, try to use channels
+         * passed as an argument to this function, or default to using channel 0. */
+        if (channels.empty()) {
+            /* No channels specified, default to 0. */
+            chans = std::vector<size_t>{0};
+        } else {
+            /* Use the channels from the function argument. */
+            chans = channels;
+        }
+    }
+
+    for (auto &ch : chans) {
+        SoapySDR::logf(SOAPY_SDR_INFO, "Using channel %zu", ch);
+    }
+
+    const std::vector<size_t> &channelIDs = chans;
     for(size_t i=0; i<channelIDs.size(); ++i)
     {
         config.channelID = channelIDs[i];