rfnoc: Add option to disable flow control on rx streaming

Disabling this feature will allow the USRP to send a continuous stream
of Rx data to a host machine without throttling due to lack of flow
control credits. This is unnecessary overhead on lossless transports
such as pcie or aurora.

Usage: add 'enable_fc=false' to stream_args.args

Signed-off-by: mattprost <matt.prost@ni.com>

2 files changed, 52 insertions, 19 deletions

diff --git a/host/lib/usrp/mpmd/mpmd_link_if_ctrl_udp.cpp b/host/lib/usrp/mpmd/mpmd_link_if_ctrl_udp.cpp
index d5be57cd9..6fc36bf72 100644
--- a/host/lib/usrp/mpmd/mpmd_link_if_ctrl_udp.cpp
+++ b/host/lib/usrp/mpmd/mpmd_link_if_ctrl_udp.cpp
@@ -12,6 +12,7 @@
 #include <uhd/transport/udp_constants.hpp>
 #include <uhd/transport/udp_simple.hpp>
 #include <uhd/transport/udp_zero_copy.hpp>
+#include <uhd/utils/cast.hpp>
 #include <uhdlib/rfnoc/rfnoc_common.hpp>
 #include <uhdlib/transport/udp_boost_asio_link.hpp>
 #include <uhdlib/transport/udp_common.hpp>
@@ -283,6 +284,9 @@ uhd::transport::both_links_t mpmd_link_if_ctrl_udp::get_link(const size_t link_i
     const std::string udp_port = _udp_info.at(ip_addr).udp_port;
 
     const size_t link_rate = get_link_rate(link_idx);
+    const bool enable_fc   = not link_args.has_key("enable_fc")
+                           || uhd::cast::from_str<bool>(link_args.get("enable_fc"));
+    const bool lossy_xport = enable_fc;
     const bool use_dpdk = _mb_args.has_key("use_dpdk");  // FIXME use constrained device args
     link_params_t default_link_params;
     default_link_params.num_send_frames = MPMD_ETH_NUM_FRAMES;
@@ -327,8 +331,9 @@ uhd::transport::both_links_t mpmd_link_if_ctrl_udp::get_link(const size_t link_i
             link_params.send_buff_size,
             link,
             link_params.recv_buff_size,
+            lossy_xport,
             true,
-            true);
+            enable_fc);
 #else
         UHD_LOG_WARNING("MPMD", "Cannot create DPDK transport, falling back to UDP");
 #endif
@@ -338,8 +343,13 @@ uhd::transport::both_links_t mpmd_link_if_ctrl_udp::get_link(const size_t link_i
         link_params,
         link_params.recv_buff_size,
         link_params.send_buff_size);
-    return std::make_tuple(
-        link, link_params.send_buff_size, link, link_params.recv_buff_size, true, false);
+    return std::make_tuple(link,
+        link_params.send_buff_size,
+        link,
+        link_params.recv_buff_size,
+        lossy_xport,
+        false,
+        enable_fc);
 }
 
 size_t mpmd_link_if_ctrl_udp::get_num_links() const
diff --git a/host/lib/usrp/mpmd/mpmd_mb_iface.cpp b/host/lib/usrp/mpmd/mpmd_mb_iface.cpp
index a24be5c57..70e982fc7 100644
--- a/host/lib/usrp/mpmd/mpmd_mb_iface.cpp
+++ b/host/lib/usrp/mpmd/mpmd_mb_iface.cpp
@@ -165,9 +165,15 @@ uhd::rfnoc::chdr_ctrl_xport::sptr mpmd_mboard_impl::mpmd_mb_iface::make_ctrl_tra
     const size_t link_idx = _local_device_id_map.at(local_device_id);
     uhd::transport::send_link_if::sptr send_link;
     uhd::transport::recv_link_if::sptr recv_link;
-    std::tie(send_link, std::ignore, recv_link, std::ignore, std::ignore, std::ignore) =
-        _link_if_mgr->get_link(
-            link_idx, uhd::transport::link_type_t::CTRL, uhd::device_addr_t());
+    std::tie(send_link,
+        std::ignore,
+        recv_link,
+        std::ignore,
+        std::ignore,
+        std::ignore,
+        std::ignore) = _link_if_mgr->get_link(link_idx,
+        uhd::transport::link_type_t::CTRL,
+        uhd::device_addr_t());
 
     /* Associate local device ID with the adapter */
     _adapter_map[local_device_id] = send_link->get_send_adapter_id();
@@ -211,11 +217,17 @@ mpmd_mboard_impl::mpmd_mb_iface::make_rx_data_transport(
 
     uhd::transport::send_link_if::sptr send_link;
     uhd::transport::recv_link_if::sptr recv_link;
-    bool lossy_xport, packet_fc;
+    bool lossy_xport, packet_fc, enable_fc;
     size_t recv_buff_size;
-    std::tie(send_link, std::ignore, recv_link, recv_buff_size, lossy_xport, packet_fc) =
-        _link_if_mgr->get_link(
-            link_idx, uhd::transport::link_type_t::RX_DATA, xport_args);
+    std::tie(send_link,
+        std::ignore,
+        recv_link,
+        recv_buff_size,
+        lossy_xport,
+        packet_fc,
+        enable_fc) = _link_if_mgr->get_link(link_idx,
+        uhd::transport::link_type_t::RX_DATA,
+        xport_args);
 
     /* Associate local device ID with the adapter */
     _adapter_map[local_sep_addr.first] = send_link->get_send_adapter_id();
@@ -226,14 +238,19 @@ mpmd_mboard_impl::mpmd_mb_iface::make_rx_data_transport(
 
     const double ratio = 1.0 / 32;
 
-    // Configure flow control frequency to use either bytes only or packets only
     uhd::rfnoc::stream_buff_params_t fc_freq;
-    if (packet_fc) {
-        fc_freq = {uhd::rfnoc::MAX_FC_FREQ_BYTES,
-            static_cast<uint32_t>(std::ceil(recv_link->get_num_recv_frames() * ratio))};
+    if (enable_fc) {
+        // Configure flow control frequency to use either bytes only or packets only
+        if (packet_fc) {
+            fc_freq = {uhd::rfnoc::MAX_FC_FREQ_BYTES,
+                static_cast<uint32_t>(
+                    std::ceil(recv_link->get_num_recv_frames() * ratio))};
+        } else {
+            fc_freq = {static_cast<uint64_t>(std::ceil(double(recv_buff_size) * ratio)),
+                uhd::rfnoc::MAX_FC_FREQ_PKTS};
+        }
     } else {
-        fc_freq = {static_cast<uint64_t>(std::ceil(double(recv_buff_size) * ratio)),
-            uhd::rfnoc::MAX_FC_FREQ_PKTS};
+        fc_freq = {0, 0};
     }
 
     stream_buff_params_t fc_headroom = {0, 0};
@@ -306,9 +323,15 @@ mpmd_mboard_impl::mpmd_mb_iface::make_tx_data_transport(
     uhd::transport::send_link_if::sptr send_link;
     uhd::transport::recv_link_if::sptr recv_link;
     bool lossy_xport;
-    std::tie(send_link, std::ignore, recv_link, std::ignore, lossy_xport, std::ignore) =
-        _link_if_mgr->get_link(
-            link_idx, uhd::transport::link_type_t::TX_DATA, xport_args);
+    std::tie(send_link,
+        std::ignore,
+        recv_link,
+        std::ignore,
+        lossy_xport,
+        std::ignore,
+        std::ignore) = _link_if_mgr->get_link(link_idx,
+        uhd::transport::link_type_t::TX_DATA,
+        xport_args);
 
     /* Associate local device ID with the adapter */
     _adapter_map[local_sep_addr.first] = send_link->get_send_adapter_id();