Legacy Initialization, Analog Audio App, and Aliasing fixes. (#3052)

* Added PRO button to analog_audio.cpp for debugging metallic ringing sounds in Audio app. Ensured consitency to 4MHz in analog_audio.cpp

* Restored blutooth after loss.

* Added several sampling rates to analog_audio for testing.

* Ran format-code.sh

* Fixed 0x03 mode for DC/Q-INV/Q-SHFT being set at every tuning and sample rate change. This was the root cause for loss of bluetooth before. Sample rate, and frequency can now be changed without need for manually resetting DC/Q-INV/Q-SHIFT settings. Updated method for setting frequncies in praline so that we have more testing options.

* Ran format-code.sh and cleaned up stale comments.

* Addressed comments, and removed commented line, opting for higher register values, 5E and 5D. Added WFM Debug View to support testing demodulation ringing.

* Addressed comments in PR conversation to clean comments and ensure consistency at initializtion accross updated methods and displays.

* Ran format-code.sh

* Set initial legacy state. Improved readability of clocking initialization settings. Updated set_sampling_frequency, and udpate_bandwidth to set decimation values in the fpga_registers to avoid aliasing in low band frequencies.

* Updated clock_manager to use correct clock and clock parameters for audio pll. Ran format-code.sh.

firmware/application/receiver_model.cpp

@@ -34,12 +34,6 @@
 #include "dsp_iir_config.hpp"
 #include "utility.hpp"
 
-#ifdef PRALINE
-extern "C" {
-#include "fpga_bridge.h"
-}
-#endif
-
 using namespace hackrf::one;
 using namespace portapack;
 
@@ -312,17 +306,6 @@ void ReceiverModel::update_tuning_frequency() {
     // TODO: use positive offset if freq < offset.
     if (enabled_) {
         radio::set_tuning_frequency(target_frequency() + hidden_offset + tuning_offset());
-
-#ifdef PRALINE
-        /* Praline: Must re-apply baseband filter after frequency change
-         * Reference: hackrf_usb radio.c radio_set_frequency()
-         *
-         * Different frequency ranges may use different quarter-shift modes,
-         * which affects the required LPF bandwidth. For now we just
-         * recalculate the filter to be safe.
-         */
-        update_baseband_bandwidth();
-#endif
     }
 }
 
@@ -334,20 +317,25 @@ void ReceiverModel::set_hidden_offset(rf::Frequency offset) {
 void ReceiverModel::update_baseband_bandwidth() {
     if (enabled_) {
 #ifdef PRALINE
-        /* Praline: LPF bandwidth calculation
-         * Reference: hackrf_usb radio.c radio_set_filter()
+        /*
+         * PRALINE LPF bandwidth calculation from GSG hackrf_usb radio.c:
          *
-         * LPF = (sample_rate * 3) / 8
-         * Plus additional offset if quarter-shift is enabled (not implemented yet)
+         * Base: (sample_rate * 3) / 8
+         * If quarter-shift enabled: add (AFE_rate / 8) * 2
          */
-        uint32_t lpf_bandwidth = (sampling_rate() * 3) / 8;
+        uint32_t sample_rate = sampling_rate();
+        uint32_t lpf_bandwidth = (sample_rate * 3) / 8;
 
-        // For now, quarter-shift is disabled, so no offset added
-        // When quarter-shift is implemented:
-        // if (quarter_shift_enabled) {
-        //     uint32_t offset = (sampling_rate() << decimation_n) / 8;
-        //     lpf_bandwidth += offset * 2;
-        // }
+        // Check if quarter-shift is enabled (FPGA register 1, bits 2-3)
+        uint32_t fpga_ctrl = radio::debug::fpga::register_read(1);
+        uint8_t quarter_shift = (fpga_ctrl >> 2) & 0x03;
+
+        if (quarter_shift != 0) {
+            // Get resampling factor from clock manager
+            uint8_t resampling_n = portapack::clock_manager.get_resampling_n();
+            uint32_t offset = (sample_rate << resampling_n) / 8;  // AFE_rate / 8
+            lpf_bandwidth += offset * 2;
+        }
 
         radio::set_baseband_filter_bandwidth_rx(lpf_bandwidth);
 #else
@@ -366,6 +354,12 @@ void ReceiverModel::update_sampling_rate() {
         radio::set_baseband_rate(sampling_rate());
     }
     update_tuning_frequency();
+
+#ifdef PRALINE
+    // GSG reference: re-apply frequency after sample rate change
+    // This reconfigures LPF bandwidth based on new decimation
+    update_baseband_bandwidth();
+#endif
 }
 
 void ReceiverModel::update_lna() {