ad9361: Reconfigure RF and baseband DC offset correction

Addressed and related issues:

    #186 "B200: Catalina RX signal distortion"
    #821 "Incorrect behavior with auto DC Offset correction turnned off"
    #820 "Rx DC Offset Correction Convergence on B2xx Dependent on Master Clock Rate"
    #755 "Demodulate IQ signal amplitude oscillation on B210 at 200 MHz carrier"

Due to recent change "ad9361: Invert phase on Rx LNA bypass path", we
now have uniform phase alignment across the entire gain range. This
drastically improves performance of RF DC tracking - not to be confused
with the - active and input dependent - baseband (BB) DC tracking loop.

RF DC tracking is not affected by input signals and updates during gain
changes. The updated configuration provides improved DC suppression for
operation whether BB tracking loop is enabled or disabled.

New behavior differs from the previous case where disabling BB tracking
would clear all - static and active - calibration tables. Now, static
correction tables are not wiped when BB tracking is turned off.

Signed-off-by: Tom Tsou <tom.tsou@ettus.com>

2 files changed, 39 insertions, 37 deletions

diff --git a/host/lib/usrp/common/ad9361_driver/ad9361_device.cpp b/host/lib/usrp/common/ad9361_driver/ad9361_device.cpp
index c488d0848..4ceccc0d9 100644
--- a/host/lib/usrp/common/ad9361_driver/ad9361_device.cpp
+++ b/host/lib/usrp/common/ad9361_driver/ad9361_device.cpp
@@ -773,16 +773,16 @@ void ad9361_device_t::_calibrate_rf_dc_offset()
         count++;
         boost::this_thread::sleep(boost::posix_time::milliseconds(50));
     }
+
+    _io_iface->poke8(0x18b, 0x8d); // Enable RF DC tracking
 }
 
-void ad9361_device_t::_configure_bb_rf_dc_tracking(const bool on)
+void ad9361_device_t::_configure_bb_dc_tracking()
 {
-    if(on)
-    {
-        _io_iface->poke8(0x18b, 0xad); // Enable BB and RF DC tracking
-    } else {
-        _io_iface->poke8(0x18b, 0x83); // Disable BB and RF DC tracking
-    }
+    if (_use_dc_offset_tracking)
+        _io_iface->poke8(0x18b, 0xad); // Enable BB tracking
+    else
+        _io_iface->poke8(0x18b, 0x8d); // Disable BB tracking
 }
 
 void ad9361_device_t::_configure_rx_iq_tracking()
@@ -1542,7 +1542,7 @@ void ad9361_device_t::initialize()
     _rx2_gain = 0;
     _tx1_gain = 0;
     _tx2_gain = 0;
-    _use_dc_offset_correction = true;
+    _use_dc_offset_tracking = true;
     _use_iq_balance_tracking = true;
     _rx1_agc_mode = GAIN_MODE_SLOW_AGC;
     _rx2_agc_mode = GAIN_MODE_SLOW_AGC;
@@ -1716,8 +1716,13 @@ void ad9361_device_t::initialize()
     _calibrate_rf_dc_offset();
     _calibrate_tx_quadrature();
     _calibrate_rx_quadrature();
-    _configure_bb_rf_dc_tracking(_use_dc_offset_correction);
 
+    /*
+     * Rx BB DC and IQ tracking are both disabled by calibration at this
+     * point. Only issue commands if tracking needs to be turned on.
+     */
+    if (_use_dc_offset_tracking)
+        _configure_bb_dc_tracking();
     if (_use_iq_balance_tracking)
         _configure_rx_iq_tracking();
 
@@ -1846,8 +1851,13 @@ double ad9361_device_t::set_clock_rate(const double req_rate)
     _calibrate_rf_dc_offset();
     _calibrate_tx_quadrature();
     _calibrate_rx_quadrature();
-    _configure_bb_rf_dc_tracking(_use_dc_offset_correction);
 
+    /*
+     * Rx BB DC and IQ tracking are both disabled by calibration at this
+     * point. Only issue commands if tracking needs to be turned on.
+     */
+    if (_use_dc_offset_tracking)
+        _configure_bb_dc_tracking();
     if (_use_iq_balance_tracking)
         _configure_rx_iq_tracking();
 
@@ -2007,8 +2017,9 @@ double ad9361_device_t::tune(direction_t direction, const double value)
         /* Run the calibration algorithms. */
         _calibrate_rf_dc_offset();
         _calibrate_tx_quadrature();
-        _configure_bb_rf_dc_tracking(_use_dc_offset_correction);
 
+        if (_use_dc_offset_tracking)
+            _configure_bb_dc_tracking();
         if (_use_iq_balance_tracking)
             _configure_rx_iq_tracking();
         else
@@ -2174,33 +2185,24 @@ double ad9361_device_t::get_average_temperature(const double cal_offset, const s
     return d_temp;
 }
 
+/*
+ * Enable/Disable DC offset tracking
+ *
+ * Only disable BB tracking while leaving static RF and BB DC calibrations enabled.
+ * According to correspondance from ADI, turning off Rx BB DC tracking clears the
+ * correction words so we don't need to be concerned with leaving the calibration
+ * in a bad state upon disabling. Testing also confirms this behavior.
+ *
+ * Note that Rx IQ tracking does not show similar state clearing behavior when
+ * disabled.
+ */
 void ad9361_device_t::set_dc_offset_auto(direction_t direction, const bool on)
 {
-    if(direction == RX)
-    {
-         _use_dc_offset_correction = on;
-         _configure_bb_rf_dc_tracking(_use_dc_offset_correction);
-        if(on)
-        {
-            _io_iface->poke8(0x182, (_io_iface->peek8(0x182) & (~((1 << 7) | (1 << 6) | (1 << 3) | (1 << 2))))); //Clear force bits
-            //Do a single shot DC offset cal before enabling tracking (Not possible if not in ALERT state. Is it necessary?)
-        } else {
-            //clear current config values
-            _io_iface->poke8(0x182, (_io_iface->peek8(0x182) | ((1 << 7) | (1 << 6) | (1 << 3) | (1 << 2)))); //Set input A and input B&C force enable bits
-            _io_iface->poke8(0x174, 0x00);
-            _io_iface->poke8(0x175, 0x00);
-            _io_iface->poke8(0x176, 0x00);
-            _io_iface->poke8(0x177, 0x00);
-            _io_iface->poke8(0x178, 0x00);
-            _io_iface->poke8(0x17D, 0x00);
-            _io_iface->poke8(0x17E, 0x00);
-            _io_iface->poke8(0x17F, 0x00);
-            _io_iface->poke8(0x180, 0x00);
-            _io_iface->poke8(0x181, 0x00);
-        }
+    if (direction == RX) {
+        _use_dc_offset_tracking = on;
+        _configure_bb_dc_tracking();
     } else {
-        // DC offset is removed during TX quad cal
-        throw uhd::runtime_error("[ad9361_device_t] [set_iq_balance_auto] INVALID_CODE_PATH");
+        throw uhd::runtime_error("[ad9361_device_t] [set_dc_offset_auto] Tx DC tracking not supported");
     }
 }
 
diff --git a/host/lib/usrp/common/ad9361_driver/ad9361_device.h b/host/lib/usrp/common/ad9361_driver/ad9361_device.h
index 8281ec9e5..f9bcd3a5e 100644
--- a/host/lib/usrp/common/ad9361_driver/ad9361_device.h
+++ b/host/lib/usrp/common/ad9361_driver/ad9361_device.h
@@ -186,7 +186,7 @@ private:    //Methods
     double _tune_helper(direction_t direction, const double value);
     double _setup_rates(const double rate);
     double _get_temperature(const double cal_offset, const double timeout = 0.1);
-    void _configure_bb_rf_dc_tracking(const bool on);
+    void _configure_bb_dc_tracking();
     void _configure_rx_iq_tracking();
     void _setup_agc(chain_t chain, gain_mode_t gain_mode);
     void _set_fir_taps(direction_t direction, chain_t chain, const std::vector<boost::int16_t>& taps);
@@ -259,7 +259,7 @@ private:    //Members
     chip_regs_t         _regs;
     //Synchronization
     boost::recursive_mutex  _mutex;
-    bool _use_dc_offset_correction;
+    bool _use_dc_offset_tracking;
     bool _use_iq_balance_tracking;
 };