mpm: Add rpc_version key in device find routine

This adds a new key to the discovery information coming from MPM
devices (rpc_version). The purpose of this is to smooth a transition to
alternative RPC subsystems other than mprpc.

If a device reports a different RPC version than supported by UHD, it
can still be found, but cannot be used for UHD sessions.

host/lib/usrp/mpmd/mpmd_find.cpp

@@ -17,7 +17,9 @@
 #include <uhdlib/utils/prefs.hpp>
 #include <uhdlib/utils/serial_number.hpp>
 #include <boost/algorithm/string.hpp>
+#include <algorithm>
 #include <future>
+#include <iterator>
 #ifdef HAVE_DPDK
 #    include <uhdlib/transport/dpdk/common.hpp>
 #endif
@@ -113,6 +115,7 @@ device_addrs_t mpmd_find_with_addr(
                 new_addr[value[0]] = value[1];
             }
         }
+        new_addr[RPC_VERSION_KEY] = new_addr.get(RPC_VERSION_KEY, DEFAULT_RPC_VERSION);
         addrs.push_back(new_addr);
     }
     return addrs;
@@ -258,8 +261,15 @@ device_addrs_t mpmd_find(const device_addr_t& hint_)
     if (check_reachability) {
         std::vector<std::future<boost::optional<device_addr_t>>> reachability_tasks;
         for (const auto& mpm_dev : bcast_mpm_devs) {
+            if (mpm_dev.get(RPC_VERSION_KEY, DEFAULT_RPC_VERSION) == RPC_VERSION) {
+                reachability_tasks.emplace_back(
+                    std::async(std::launch::async, [mpm_dev]() {
+                        return mpmd_mboard_impl::is_device_reachable(mpm_dev);
+                    }));
+            } else {
                 reachability_tasks.emplace_back(std::async(std::launch::async,
-                [mpm_dev]() { return mpmd_mboard_impl::is_device_reachable(mpm_dev); }));
+                    []() { return boost::optional<device_addr_t>{}; }));
+            }
         }
         // Variable i is used to index reachability_tasks as well as bcast_mpm_devs (both
         // of same size by construction), therefore using iterators here is less elegant.
@@ -272,8 +282,15 @@ device_addrs_t mpmd_find(const device_addr_t& hint_)
                     flag_dev_as_unreachable(bcast_mpm_devs[i]));
             }
         }
-    } else {
+    } else if (find_all) {
         filtered_mpm_devs = bcast_mpm_devs;
+    } else {
+        std::copy_if(bcast_mpm_devs.cbegin(),
+            bcast_mpm_devs.cend(),
+            std::back_inserter(filtered_mpm_devs),
+            [](const device_addr_t& dev) {
+                return dev.get(RPC_VERSION_KEY, DEFAULT_RPC_VERSION) == RPC_VERSION;
+            });
     }
 
     if (filtered_mpm_devs.empty() and not bcast_mpm_devs.empty()) {

host/lib/usrp/mpmd/mpmd_impl.cpp

@@ -149,6 +149,15 @@ const std::string mpmd_impl::MPM_ECHO_CMD               = "MPM-ECHO";
 mpmd_impl::mpmd_impl(const device_addr_t& device_args)
     : rfnoc_device(), _device_args(device_args)
 {
+    UHD_ASSERT_THROW(device_args.has_key(RPC_VERSION_KEY));
+    if (device_args.get(RPC_VERSION_KEY, DEFAULT_RPC_VERSION) != RPC_VERSION) {
+        UHD_LOG_THROW(uhd::runtime_error,
+            "MPMD",
+            "RPC version mismatch. Expected: "
+                << RPC_VERSION
+                << " Actual: " << device_args.get(RPC_VERSION_KEY, DEFAULT_RPC_VERSION)
+                << ". Please update the version of MPM on your USRP device.");
+    }
     const device_addrs_t mb_args_without_prefs = separate_device_addr(device_args);
     device_addrs_t mb_args;
     for (size_t i = 0; i < mb_args_without_prefs.size(); ++i) {

host/lib/usrp/mpmd/mpmd_impl.hpp

@@ -38,6 +38,12 @@ static constexpr size_t MPMD_SHORT_RPC_TIMEOUT = 2000;
 static constexpr size_t MPMD_CLAIMER_RPC_TIMEOUT = 10000;
 //! Ethernet address for management and RPC communication
 static const std::string MGMT_ADDR_KEY = "mgmt_addr";
+//! RPC version
+static const std::string RPC_VERSION_KEY = "rpc_version";
+static const std::string RPC_VERSION     = "1";
+// Older devices did not provide an RPC version, but they were all using
+// mprpc, aka version 1.
+static const std::string DEFAULT_RPC_VERSION = "1";
 
 namespace uhd { namespace mpmd {
 

mpm/python/usrp_mpm/discovery.py

@@ -15,6 +15,8 @@ from usrp_mpm.mpmutils import set_proc_title, to_binary_str
 RESPONSE_PREAMBLE = b"USRP-MPM"
 RESPONSE_SEP = b";"
 RESPONSE_CLAIMED_KEY = b"claimed"
+# 1: mprpc
+RPC_VERSION = b"1"
 # A buffer size large enough to capture any UDP packet we receive on the
 # discovery socket
 MAX_SOCK_BUFSIZ = 9000
@@ -57,6 +59,7 @@ def _discovery_process(state, discovery_addr):
             + [b"serial=" + state.dev_serial.value]
             + [b"name=" + state.dev_name.value]
             + [b"fpga=" + state.dev_fpga_type.value]
+            + [b"rpc_version=" + RPC_VERSION]
             + [RESPONSE_CLAIMED_KEY + to_binary_str("={}".format(state.claim_status.value))]
         )