From bd8385464e611906cfc8effbaf43b0345cd3525c Mon Sep 17 00:00:00 2001
From: Mark Thompson <129641948+NotherNgineer@users.noreply.github.com>
Date: Sun, 28 Jan 2024 10:02:11 -0600
Subject: [PATCH] Tuner code readability (no functional change) (#1820)

---
 firmware/application/radio.cpp   |  2 ++
 firmware/application/rf_path.hpp |  4 +--
 firmware/application/tuning.cpp  | 43 ++++++++++++++++----------------
 3 files changed, 25 insertions(+), 24 deletions(-)

diff --git a/firmware/application/radio.cpp b/firmware/application/radio.cpp
index 37c719c26..b6fd614d4 100644
--- a/firmware/application/radio.cpp
+++ b/firmware/application/radio.cpp
@@ -184,11 +184,13 @@ bool set_tuning_frequency(const rf::Frequency frequency) {
     if (tuning_config.is_valid()) {
         first_if.disable();
 
+        // Program first local oscillator frequency (if there is one) into RFFC507x
         if (tuning_config.first_lo_frequency) {
             first_if.set_frequency(tuning_config.first_lo_frequency);
             first_if.enable();
         }
 
+        // Program second local oscillator frequency into MAX283x
         const auto result_second_if = second_if->set_frequency(tuning_config.second_lo_frequency);
 
         rf_path.set_band(tuning_config.rf_path_band);
diff --git a/firmware/application/rf_path.hpp b/firmware/application/rf_path.hpp
index d6622f80f..e886624d8 100644
--- a/firmware/application/rf_path.hpp
+++ b/firmware/application/rf_path.hpp
@@ -39,8 +39,8 @@ enum class Direction {
 
 namespace path {
 
-constexpr FrequencyRange band_low{0, 2170000000};
-constexpr FrequencyRange band_high{2740000000, 7250000000};
+constexpr FrequencyRange band_low{0, 2170'000'000};
+constexpr FrequencyRange band_high{2740'000'000, 7250'000'000};
 constexpr FrequencyRange band_mid{band_low.maximum, band_high.minimum};
 
 enum class Band {
diff --git a/firmware/application/tuning.cpp b/firmware/application/tuning.cpp
index 5024e8cb0..f1425a52f 100644
--- a/firmware/application/tuning.cpp
+++ b/firmware/application/tuning.cpp
@@ -26,44 +26,43 @@
 namespace tuning {
 namespace config {
 
-namespace {
-
+// Low band <2170 Mhz:
 constexpr rf::Frequency low_band_second_lo_frequency(const rf::Frequency target_frequency) {
-    return 2650000000 - (target_frequency / 7);
-}
-
-constexpr rf::Frequency high_band_second_lo_regions_2_and_3(const rf::Frequency target_frequency) {
-    return (target_frequency < 5100000000)
-               ? (2350000000 + ((target_frequency - 3600000000) / 5))
-               : (2500000000 + ((target_frequency - 5100000000) / 9));
-}
-
-constexpr rf::Frequency high_band_second_lo_frequency(const rf::Frequency target_frequency) {
-    return (target_frequency < 3600000000)
-               ? (2170000000 + (((target_frequency - 2740000000) * 57) / 86))
-               : high_band_second_lo_regions_2_and_3(target_frequency);
+    return 2650'000'000 - (target_frequency / 7);
 }
 
 Config low_band(const rf::Frequency target_frequency) {
-    const rf::Frequency first_lo_frequency = target_frequency + low_band_second_lo_frequency(target_frequency);
-    const rf::Frequency second_lo_frequency = first_lo_frequency - target_frequency;
+    const rf::Frequency second_lo_frequency = low_band_second_lo_frequency(target_frequency);
+    const rf::Frequency first_lo_frequency = target_frequency + second_lo_frequency;
     const bool mixer_invert = true;
     return {first_lo_frequency, second_lo_frequency, rf::path::Band::Low, mixer_invert};
 }
 
+// Mid band 2170-2740 Mhz:
 Config mid_band(const rf::Frequency target_frequency) {
-    return {0, target_frequency, rf::path::Band::Mid, false};
+    const rf::Frequency second_lo_frequency = target_frequency;
+    const rf::Frequency first_lo_frequency = 0;
+    const bool mixer_invert = false;
+    return {first_lo_frequency, second_lo_frequency, rf::path::Band::Mid, mixer_invert};
+}
+
+// High band >2740 Mhz:
+constexpr rf::Frequency high_band_second_lo_frequency(const rf::Frequency target_frequency) {
+    if (target_frequency < 3600'000'000)
+        return (2170'000'000 + (((target_frequency - 2740'000'000) * 57) / 86));
+    else if (target_frequency < 5100'000'000)
+        return (2350'000'000 + ((target_frequency - 3600'000'000) / 5));
+    else
+        return (2500'000'000 + ((target_frequency - 5100'000'000) / 9));
 }
 
 Config high_band(const rf::Frequency target_frequency) {
-    const rf::Frequency first_lo_frequency = target_frequency - high_band_second_lo_frequency(target_frequency);
-    const rf::Frequency second_lo_frequency = target_frequency - first_lo_frequency;
+    const rf::Frequency second_lo_frequency = high_band_second_lo_frequency(target_frequency);
+    const rf::Frequency first_lo_frequency = target_frequency - second_lo_frequency;
     const bool mixer_invert = false;
     return {first_lo_frequency, second_lo_frequency, rf::path::Band::High, mixer_invert};
 }
 
-} /* namespace */
-
 Config create(const rf::Frequency target_frequency) {
     /* TODO: This is some lame code. */
     if (rf::path::band_low.contains(target_frequency)) {