usrp2: Re-add ability to modulate in the DAC

This partially reverts b29e80cc. That commit fixed a bug with numerical
overflows, but also removed the ability to tune using the DAC,
effectively reducing the DSP tuning range.

This commit allows to tune within +/- 200 MHz using a combination of
both the DAC and the DSP tuning in the FPGA.

Reviewed-by: Derek Kozek <derek.kozel@ettus.com>

3 files changed, 85 insertions, 7 deletions

diff --git a/host/lib/usrp/usrp2/codec_ctrl.cpp b/host/lib/usrp/usrp2/codec_ctrl.cpp
index c3e7b332f..5c1c006fb 100644
--- a/host/lib/usrp/usrp2/codec_ctrl.cpp
+++ b/host/lib/usrp/usrp2/codec_ctrl.cpp
@@ -179,6 +179,11 @@ public:
         }
     }
 
+    size_t get_tx_interpolation() const
+    {
+        return 4;
+    }
+
 private:
     ad9777_regs_t _ad9777_regs;
     ads62p44_regs_t _ads62p44_regs;
diff --git a/host/lib/usrp/usrp2/codec_ctrl.hpp b/host/lib/usrp/usrp2/codec_ctrl.hpp
index e32b508e9..ac808e357 100644
--- a/host/lib/usrp/usrp2/codec_ctrl.hpp
+++ b/host/lib/usrp/usrp2/codec_ctrl.hpp
@@ -56,6 +56,13 @@ public:
 
     virtual void set_rx_digital_fine_gain(double gain) = 0;
 
+    /*! Return the internal interpolation on the TX side. This is the factor
+     *  between the rate of incoming samples and rate at which the DAC is
+     *  actually clocked. Values > 1 will enable features, such as internal
+     *  modulation.
+     */
+    virtual size_t get_tx_interpolation() const = 0;
+
 };
 
 #endif /* INCLUDED_CODEC_CTRL_HPP */
diff --git a/host/lib/usrp/usrp2/usrp2_impl.cpp b/host/lib/usrp/usrp2/usrp2_impl.cpp
index 88591333a..d6ab11969 100644
--- a/host/lib/usrp/usrp2/usrp2_impl.cpp
+++ b/host/lib/usrp/usrp2/usrp2_impl.cpp
@@ -622,21 +622,44 @@ usrp2_impl::usrp2_impl(const device_addr_t &_device_addr) :
         // create tx dsp control objects
         ////////////////////////////////////////////////////////////////
         _mbc[mb].tx_dsp = tx_dsp_core_200::make(
-            _mbc[mb].wbiface, U2_REG_SR_ADDR(SR_TX_DSP), U2_REG_SR_ADDR(SR_TX_CTRL), USRP2_TX_ASYNC_SID
+            _mbc[mb].wbiface,
+            U2_REG_SR_ADDR(SR_TX_DSP),
+            U2_REG_SR_ADDR(SR_TX_CTRL),
+            USRP2_TX_ASYNC_SID
         );
         _mbc[mb].tx_dsp->set_link_rate(USRP2_LINK_RATE_BPS);
+        { // This scope can be removed once we're able to do named captures
+        auto this_tx_dsp = _mbc[mb].tx_dsp; // This can then also go away
         _tree->access<double>(mb_path / "tick_rate")
-            .add_coerced_subscriber(boost::bind(&tx_dsp_core_200::set_tick_rate, _mbc[mb].tx_dsp, _1));
+            .add_coerced_subscriber([this_tx_dsp](const double rate){
+                this_tx_dsp->set_tick_rate(rate);
+            })
+        ;
         _tree->create<meta_range_t>(mb_path / "tx_dsps/0/rate/range")
-            .set_publisher(boost::bind(&tx_dsp_core_200::get_host_rates, _mbc[mb].tx_dsp));
+            .set_publisher([this_tx_dsp](){
+                return this_tx_dsp->get_host_rates();
+            })
+        ;
         _tree->create<double>(mb_path / "tx_dsps/0/rate/value")
             .set(1e6) //some default
-            .set_coercer(boost::bind(&tx_dsp_core_200::set_host_rate, _mbc[mb].tx_dsp, _1))
-            .add_coerced_subscriber(boost::bind(&usrp2_impl::update_tx_samp_rate, this, mb, 0, _1));
+            .set_coercer([this_tx_dsp](const double rate){
+                return this_tx_dsp->set_host_rate(rate);
+            })
+            .add_coerced_subscriber([this, mb](const double rate){
+                this->update_tx_samp_rate(mb, 0, rate);
+            })
+        ;
+        } // End of non-C++14 scope (to release reference to this_tx_dsp)
         _tree->create<double>(mb_path / "tx_dsps/0/freq/value")
-            .set_coercer(boost::bind(&tx_dsp_core_200::set_freq, _mbc[mb].tx_dsp, _1));
+            .set_coercer([this, mb](const double rate){
+                return this->set_tx_dsp_freq(mb, rate);
+            })
+        ;
         _tree->create<meta_range_t>(mb_path / "tx_dsps/0/freq/range")
-            .set_publisher(boost::bind(&tx_dsp_core_200::get_freq_range, _mbc[mb].tx_dsp));
+            .set_publisher([this, mb](){
+                return this->get_tx_dsp_freq_range(mb);
+            })
+        ;
 
         //setup dsp flow control
         const double ups_per_sec = device_args_i.cast<double>("ups_per_sec", 20);
@@ -810,6 +833,49 @@ void usrp2_impl::set_tx_fe_corrections(const std::string &mb, const double lo_fr
     }
 }
 
+double usrp2_impl::set_tx_dsp_freq(
+    const std::string &mb,
+    const double freq_
+) {
+    double new_freq = freq_;
+    const double tick_rate =
+        _tree->access<double>("/mboards/"+mb+"/tick_rate").get();
+
+    //calculate the DAC shift (multiples of rate)
+    const int sign = boost::math::sign(new_freq);
+    const int zone = std::min(boost::math::iround(new_freq/tick_rate), 2);
+    const double dac_shift = sign*zone*tick_rate;
+    new_freq -= dac_shift; //update FPGA DSP target freq
+    UHD_LOG_TRACE("USRP2",
+        "DSP Tuning: Requested " + std::to_string(freq_/1e6) + " MHz, Using "
+        "Nyquist zone " + std::to_string(sign*zone) + ", leftover DSP tuning: "
+        + std::to_string(new_freq/1e6) + " MHz.");
+
+    //set the DAC shift (modulation mode)
+    if (zone == 0) {
+        _mbc[mb].codec->set_tx_mod_mode(0); //no shift
+    } else {
+        _mbc[mb].codec->set_tx_mod_mode(sign*4/zone); //DAC interp = 4
+    }
+
+    return _mbc[mb].tx_dsp->set_freq(new_freq) + dac_shift; //actual freq
+}
+
+meta_range_t usrp2_impl::get_tx_dsp_freq_range(const std::string &mb)
+{
+    const double dac_rate =
+        _tree->access<double>("/mboards/" + mb + "/tick_rate").get()
+        * _mbc[mb].codec->get_tx_interpolation();
+    const auto dsp_range_step = _mbc[mb].tx_dsp->get_freq_range().step();
+    // The DSP tuning rate is the entire range of the DAC clock rate. The step
+    // size is determined by the FPGA IP, however.
+    return meta_range_t(
+        -dac_rate / 2,
+        +dac_rate / 2,
+        dsp_range_step
+    );
+}
+
 #include <boost/math/special_functions/round.hpp>
 #include <boost/math/special_functions/sign.hpp>