ad9361: Removed unnecessary digital TX attenuation

- Fix ported from He. The current TX filter does not need
  the additional -6dB of headroom. Set it to zero so we
  meet our max power specs.

1 files changed, 7 insertions, 1 deletions

diff --git a/host/lib/usrp/common/ad9361_driver/ad9361_device.cpp b/host/lib/usrp/common/ad9361_driver/ad9361_device.cpp
index 3ce655c9b..97b214d7d 100644
--- a/host/lib/usrp/common/ad9361_driver/ad9361_device.cpp
+++ b/host/lib/usrp/common/ad9361_driver/ad9361_device.cpp
@@ -135,9 +135,15 @@ void ad9361_device_t::_program_fir_filter(direction_t direction, int num_taps, b
     _io_iface->poke8(base + 5, reg_numtaps | 0x1A);
     if (direction == RX) {
         _io_iface->poke8(base + 5, reg_numtaps | 0x18);
+        /* Rx Gain, set to prevent digital overflow/saturation in filters
+           0:+6dB, 1:0dB, 2:-6dB, 3:-12dB
+           page 35 of UG-671 */
         _io_iface->poke8(base + 6, 0x02); /* Also turn on -6dB Rx gain here, to stop filter overfow.*/
     } else {
-        _io_iface->poke8(base + 5, reg_numtaps | 0x19); /* Also turn on -6dB Tx gain here, to stop filter overfow.*/
+        /* Tx Gain. bit[0]. set to prevent digital overflow/saturation in filters
+           0: 0dB, 1:-6dB
+           page 25 of UG-671 */
+        _io_iface->poke8(base + 5, reg_numtaps | 0x18);
     }
 }