n310/n300: Allow gain coercion

The N310 had a different behaviour from other devices, where setting
a gain out of range would cause an assertion error. This is problematic
for two reasons:
1) Assertion errors should not be triggered by public APIs (if we throw
   public APIs, we should give a clear error message), and
2) Setting gain and frequency has a coercing behaviour on all other
   devices.

This changeset clips the gain before calling into the gain table lookup.

1 files changed, 16 insertions, 2 deletions

diff --git a/host/lib/usrp/dboard/magnesium/magnesium_radio_ctrl_impl.cpp b/host/lib/usrp/dboard/magnesium/magnesium_radio_ctrl_impl.cpp
index 405d5955e..892fa94bd 100644
--- a/host/lib/usrp/dboard/magnesium/magnesium_radio_ctrl_impl.cpp
+++ b/host/lib/usrp/dboard/magnesium/magnesium_radio_ctrl_impl.cpp
@@ -337,8 +337,15 @@ double magnesium_radio_ctrl_impl::set_tx_gain(const double gain, const size_t ch
 {
     std::lock_guard<std::mutex> l(_set_lock);
     UHD_LOG_TRACE(unique_id(), "set_tx_gain(gain=" << gain << ", chan=" << chan << ")");
+    // First, clip to valid range
+    const double clipped_gain = uhd::clip(gain, ALL_TX_MIN_GAIN, ALL_TX_MAX_GAIN);
+    if (clipped_gain != gain) {
+        UHD_LOG_WARNING(unique_id(),
+            "Channel " << chan << ": Coercing TX gain from " << gain << " dB to "
+                       << clipped_gain);
+    }
     const double coerced_gain =
-        _set_all_gain(gain, this->get_tx_frequency(chan), chan, TX_DIRECTION);
+        _set_all_gain(clipped_gain, this->get_tx_frequency(chan), chan, TX_DIRECTION);
     radio_ctrl_impl::set_tx_gain(coerced_gain, chan);
     return coerced_gain;
 }
@@ -392,8 +399,15 @@ double magnesium_radio_ctrl_impl::set_rx_gain(const double gain, const size_t ch
 {
     std::lock_guard<std::mutex> l(_set_lock);
     UHD_LOG_TRACE(unique_id(), "set_rx_gain(gain=" << gain << ", chan=" << chan << ")");
+    // First, clip to valid range
+    const double clipped_gain = uhd::clip(gain, ALL_RX_MIN_GAIN, ALL_RX_MAX_GAIN);
+    if (clipped_gain != gain) {
+        UHD_LOG_WARNING(unique_id(),
+            "Channel " << chan << ": Coercing RX gain from " << gain << " dB to "
+                       << clipped_gain);
+    }
     const double coerced_gain =
-        _set_all_gain(gain, this->get_rx_frequency(chan), chan, RX_DIRECTION);
+        _set_all_gain(clipped_gain, this->get_rx_frequency(chan), chan, RX_DIRECTION);
     radio_ctrl_impl::set_rx_gain(coerced_gain, chan);
     return coerced_gain;
 }