diff --git a/src/ria_toolkit_oss/sdr/usrp.py b/src/ria_toolkit_oss/sdr/usrp.py
index 3ae7569..44d8842 100644
--- a/src/ria_toolkit_oss/sdr/usrp.py
+++ b/src/ria_toolkit_oss/sdr/usrp.py
@@ -72,7 +72,7 @@ class USRP(SDR):
 
         # build USRP object
         usrp_args = _generate_usrp_config_string(sample_rate=sample_rate, device_dict=self.device_dict)
-        self.usrp = uhd.usrp.MultiUSRP(usrp_args)
+        self.usrp = _open_multi_usrp(usrp_args)
 
         # check if  channel arg is valid
         max_num_channels = self.usrp.get_rx_num_channels()
@@ -394,7 +394,7 @@ class USRP(SDR):
         print(f"USRP TX Gain Mode = '{gain_mode}'")
 
         config_str = _generate_usrp_config_string(sample_rate=sample_rate, device_dict=self.device_dict)
-        self.usrp = uhd.usrp.MultiUSRP(config_str)
+        self.usrp = _open_multi_usrp(config_str)
 
         # check if channel arg is valid
         max_num_channels = self.usrp.get_rx_num_channels()
@@ -563,6 +563,32 @@ class USRP(SDR):
         return {"center_frequency": True, "sample_rate": True, "gain": True}
 
 
+def _open_multi_usrp(usrp_args, *, attempts=4, settle_s=2.0):
+    """Construct a ``uhd.usrp.MultiUSRP``, retrying transient B200 USB states.
+
+    On USB USRPs (B200/B210) the ``uhd_find_devices`` enumeration that resolves
+    the device (see ``_create_device_dict``) runs immediately before the open and
+    can leave the FX3 USB controller mid-reset, so the first open fails with e.g.
+    ``RuntimeError: fx3 is in state 5``. The device settles once that
+    enumeration's USB handle is fully released — and the failed open itself nudges
+    the FX3 to reload firmware/FPGA — so we retry with a short backoff before
+    giving up. A non-transient error (bad args, genuinely absent device) is
+    re-raised immediately.
+    """
+    for attempt in range(1, attempts + 1):
+        try:
+            return uhd.usrp.MultiUSRP(usrp_args)
+        except RuntimeError as exc:
+            msg = str(exc).lower()
+            transient = ("fx3" in msg) or ("usb" in msg) or ("no devices found" in msg)
+            if not transient or attempt == attempts:
+                raise
+            print(
+                f"\033[93mUSRP open attempt {attempt}/{attempts} failed " f"({exc}); retrying in {settle_s}s…\033[0m"
+            )
+            time.sleep(settle_s)
+
+
 def _create_device_dict(identifier_value=None):
     """
     Get the dictionary of information corresponding to any unique identifier,
diff --git a/tests/agent/test_usrp_open_retry.py b/tests/agent/test_usrp_open_retry.py
new file mode 100644
index 0000000..57ddbe4
--- /dev/null
+++ b/tests/agent/test_usrp_open_retry.py
@@ -0,0 +1,91 @@
+"""Hardware-free tests for _open_multi_usrp's transient-FX3 retry.
+
+On B200/B210 the `uhd_find_devices` enumeration that runs right before opening
+can leave the FX3 USB controller mid-reset, so the first MultiUSRP open fails
+with "fx3 is in state 5". _open_multi_usrp retries transient USB states with a
+short settle; a non-transient error is re-raised immediately.
+"""
+
+from __future__ import annotations
+
+import sys
+import types
+
+import pytest
+
+
+@pytest.fixture
+def usrp_mod(monkeypatch):
+    """Import the usrp module against a stub `uhd`, with time.sleep neutered."""
+    saved_uhd = sys.modules.get("uhd")
+    saved_usrp = sys.modules.get("ria_toolkit_oss.sdr.usrp")
+
+    uhd = types.ModuleType("uhd")
+    uhd.usrp = types.SimpleNamespace(MultiUSRP=None)  # set per-test
+    sys.modules["uhd"] = uhd
+    sys.modules.pop("ria_toolkit_oss.sdr.usrp", None)
+    import ria_toolkit_oss.sdr.usrp as mod
+
+    monkeypatch.setattr(mod.time, "sleep", lambda *_a, **_k: None)
+
+    yield mod
+
+    for name, m in (("uhd", saved_uhd), ("ria_toolkit_oss.sdr.usrp", saved_usrp)):
+        if m is None:
+            sys.modules.pop(name, None)
+        else:
+            sys.modules[name] = m
+
+
+def _flaky_factory(fail_times, exc):
+    """A MultiUSRP stand-in that raises `exc` the first `fail_times` calls."""
+    calls = {"n": 0}
+
+    def make(args):
+        calls["n"] += 1
+        if calls["n"] <= fail_times:
+            raise exc
+        return f"usrp<{args}>"
+
+    make.calls = calls
+    return make
+
+
+def test_retries_transient_fx3_state_then_succeeds(usrp_mod):
+    factory = _flaky_factory(2, RuntimeError("RuntimeError: fx3 is in state 5"))
+    usrp_mod.uhd.usrp.MultiUSRP = factory
+
+    out = usrp_mod._open_multi_usrp("name=B210,", attempts=4, settle_s=0)
+
+    assert out == "usrp<name=B210,>"
+    assert factory.calls["n"] == 3  # failed twice, third succeeded
+
+
+def test_gives_up_after_attempts_and_raises_last(usrp_mod):
+    factory = _flaky_factory(99, RuntimeError("fx3 is in state 5"))
+    usrp_mod.uhd.usrp.MultiUSRP = factory
+
+    with pytest.raises(RuntimeError, match="fx3 is in state 5"):
+        usrp_mod._open_multi_usrp("name=B210,", attempts=3, settle_s=0)
+
+    assert factory.calls["n"] == 3  # exactly `attempts` tries, no infinite loop
+
+
+def test_non_transient_error_is_raised_immediately(usrp_mod):
+    factory = _flaky_factory(99, RuntimeError("EnvironmentError: no UHD images"))
+    usrp_mod.uhd.usrp.MultiUSRP = factory
+
+    with pytest.raises(RuntimeError, match="no UHD images"):
+        usrp_mod._open_multi_usrp("name=B210,", attempts=4, settle_s=0)
+
+    assert factory.calls["n"] == 1  # not retried — fails fast
+
+
+def test_success_on_first_try_does_not_retry(usrp_mod):
+    factory = _flaky_factory(0, RuntimeError("fx3 is in state 5"))
+    usrp_mod.uhd.usrp.MultiUSRP = factory
+
+    out = usrp_mod._open_multi_usrp("addr=192.168.10.2,", attempts=4, settle_s=0)
+
+    assert out == "usrp<addr=192.168.10.2,>"
+    assert factory.calls["n"] == 1