uhd: add samples per pkt option to rx streamer

4 files changed, 11 insertions, 3 deletions

diff --git a/host/include/uhd/stream.hpp b/host/include/uhd/stream.hpp
index b41c1733d..352f63e4e 100644
--- a/host/include/uhd/stream.hpp
+++ b/host/include/uhd/stream.hpp
@@ -88,6 +88,11 @@ struct UHD_API stream_args_t{
      * In the "next_burst" mode, the DSP drops incoming packets until a new burst is started.
      * In the "next_packet" mode, the DSP starts transmitting again at the next packet.
      *
+     * - spp: (samples per packet) controls the size of RX packets.
+     * When not specified, the packets are always maximum frame size.
+     * Users should specify this option to request smaller than default
+     * packets, probably with the intention of reducing packet latency.
+     *
      * The following are not implemented, but are listed for conceptual purposes:
      * - function: magnitude or phase/magnitude
      * - units: numeric units like counts or dBm
diff --git a/host/lib/usrp/b100/io_impl.cpp b/host/lib/usrp/b100/io_impl.cpp
index 692ede6d5..494d5d123 100644
--- a/host/lib/usrp/b100/io_impl.cpp
+++ b/host/lib/usrp/b100/io_impl.cpp
@@ -211,7 +211,8 @@ rx_streamer::sptr b100_impl::get_rx_stream(const uhd::stream_args_t &args_){
         - sizeof(vrt::if_packet_info_t().cid) //no class id ever used
     ;
     const size_t bpp = 2048 - hdr_size; //limited by FPGA pkt buffer size
-    const size_t spp = bpp/convert::get_bytes_per_item(args.otw_format);
+    const size_t bpi = convert::get_bytes_per_item(args.otw_format);
+    const size_t spp = unsigned(args.args.cast<double>("spp", bpp/bpi));
 
     //make the new streamer given the samples per packet
     boost::shared_ptr<sph::recv_packet_streamer> my_streamer = boost::make_shared<sph::recv_packet_streamer>(spp);
diff --git a/host/lib/usrp/e100/io_impl.cpp b/host/lib/usrp/e100/io_impl.cpp
index 92905526c..441e32a8d 100644
--- a/host/lib/usrp/e100/io_impl.cpp
+++ b/host/lib/usrp/e100/io_impl.cpp
@@ -287,7 +287,8 @@ rx_streamer::sptr e100_impl::get_rx_stream(const uhd::stream_args_t &args_){
         - sizeof(vrt::if_packet_info_t().cid) //no class id ever used
     ;
     const size_t bpp = _data_transport->get_recv_frame_size() - hdr_size;
-    const size_t spp = bpp/convert::get_bytes_per_item(args.otw_format);
+    const size_t bpi = convert::get_bytes_per_item(args.otw_format);
+    const size_t spp = unsigned(args.args.cast<double>("spp", bpp/bpi));
 
     //make the new streamer given the samples per packet
     boost::shared_ptr<sph::recv_packet_streamer> my_streamer = boost::make_shared<sph::recv_packet_streamer>(spp);
diff --git a/host/lib/usrp/usrp2/io_impl.cpp b/host/lib/usrp/usrp2/io_impl.cpp
index fd81071fb..e3fa46920 100644
--- a/host/lib/usrp/usrp2/io_impl.cpp
+++ b/host/lib/usrp/usrp2/io_impl.cpp
@@ -389,7 +389,8 @@ rx_streamer::sptr usrp2_impl::get_rx_stream(const uhd::stream_args_t &args_){
         - sizeof(vrt::if_packet_info_t().cid) //no class id ever used
     ;
     const size_t bpp = _mbc[_mbc.keys().front()].rx_dsp_xports[0]->get_recv_frame_size() - hdr_size;
-    const size_t spp = bpp/convert::get_bytes_per_item(args.otw_format);
+    const size_t bpi = convert::get_bytes_per_item(args.otw_format);
+    const size_t spp = unsigned(args.args.cast<double>("spp", bpp/bpi));
 
     //make the new streamer given the samples per packet
     boost::shared_ptr<sph::recv_packet_streamer> my_streamer = boost::make_shared<sph::recv_packet_streamer>(spp);