docs: stream_args: Clarify usage of stream_args_t::channels

This vector is no longer used with RFNoC devices. We remove references
to X300 from the example, and instead use B210 as an example.

1 files changed, 23 insertions, 15 deletions

diff --git a/host/include/uhd/stream.hpp b/host/include/uhd/stream.hpp
index 97cfc1ac5..87a5c0ace 100644
--- a/host/include/uhd/stream.hpp
+++ b/host/include/uhd/stream.hpp
@@ -128,24 +128,32 @@ struct UHD_API stream_args_t
      */
     device_addr_t args;
 
-    /*!
-     * The channels is a list of channel numbers.
-     * Leave this blank to default to channel 0 (single-channel application).
-     * Set channels for a multi-channel application.
-     * Channel mapping depends on the front-end selection (see also \ref config_subdev).
+    /*! List of channel numbers (only used by non-RFNoC devices)
+     *
+     * Note: For RFNoC devices, this value is not used. To create a streamer
+     * with multiple channels, the uhd::rfnoc::rfnoc_graph::create_tx_streamer()
+     * and uhd::rfnoc::rfnoc_graph::create_rx_streamer() API calls have a
+     * \p num_ports argument.
      *
-     * A very simple example is an X300 with two daughterboards and a subdev spec
-     * of `A:0 B:0`. This means the device has two channels available.
+     * For non-RFNoC devices (i.e., USRP1, B100, B200, N200), this argument
+     * defines how streamer channels map to the front-end selection (see also
+     * \ref config_subdev).
      *
-     * Setting `stream_args.channels = (0, 1)` therefore configures MIMO streaming
-     * from both channels. By switching the channel indexes, `stream_args.channels = (1,
-     * 0)`, the channels are switched and the first channel of the USRP is mapped to the
-     * second channel in the application.
+     * A very simple example is a B210 with a subdev spec of `A:A A:B`. This
+     * means the device has two channels available.
      *
-     * If only a single channel is used for streaming, `stream_args.channels = (1,)` would
-     * only select a single channel (in this case, the second one). When streaming
-     * a single channel from the B-side radio of a USRP, this is a more versatile solution
-     * than setting the subdev globally to "B:0".
+     * Setting `stream_args.channels = {0, 1}` therefore configures MIMO
+     * streaming from both channels. By switching the channel indexes,
+     * `stream_args.channels = {1, 0}`, the channels are switched and the first
+     * channel of the USRP is mapped to the second channel in the application.
+     *
+     * If only a single channel is used for streaming, e.g.,
+     * `stream_args.channels = {1}` would only select a single channel (in this
+     * case, the second one). When streaming a single channel from the B-side
+     * radio of a USRP, this is a more versatile solution than setting the
+     * subdev spec globally to "A:B".
+     *
+     * Leave this blank to default to channel 0 (single-channel application).
      */
     std::vector<size_t> channels;
 };