4 files changed, 76 insertions, 0 deletions

diff --git a/src/drivers/include/nvs.hpp b/src/drivers/include/nvs.hpp
index bc88f88d..d7b3dfdd 100644
--- a/src/drivers/include/nvs.hpp
+++ b/src/drivers/include/nvs.hpp
@@ -37,6 +37,12 @@ class NvsStorage {
   auto ScreenBrightness() -> std::future<uint_fast8_t>;
   auto ScreenBrightness(uint_fast8_t) -> std::future<bool>;
 
+  auto AmpMaxVolume() -> std::future<uint16_t>;
+  auto AmpMaxVolume(uint16_t) -> std::future<bool>;
+
+  auto AmpCurrentVolume() -> std::future<uint16_t>;
+  auto AmpCurrentVolume(uint16_t) -> std::future<bool>;
+
   explicit NvsStorage(std::unique_ptr<tasks::Worker>, nvs_handle_t);
   ~NvsStorage();
 
diff --git a/src/drivers/include/wm8523.hpp b/src/drivers/include/wm8523.hpp
index 6dc2e56e..b13cf34b 100644
--- a/src/drivers/include/wm8523.hpp
+++ b/src/drivers/include/wm8523.hpp
@@ -5,12 +5,32 @@
  */
 #pragma once
 
+#include <stdint.h>
 #include <cstdint>
 #include <optional>
 
 namespace drivers {
 namespace wm8523 {
 
+extern const uint16_t kAbsoluteMaxVolume;
+
+extern const uint16_t kAbsoluteMinVolume;
+
+extern const uint16_t kMaxVolumeBeforeClipping;
+
+extern const uint16_t kLineLevelReferenceVolume;
+
+extern const uint16_t kDefaultVolume;
+extern const uint16_t kDefaultMaxVolume;
+
+constexpr auto VolumeToDb(uint16_t vol) -> int_fast8_t {
+  return (vol - kLineLevelReferenceVolume) / 4;
+}
+
+constexpr auto DbToVolume(int_fast8_t db) -> uint16_t {
+  return (db * 4) + kLineLevelReferenceVolume;
+}
+
 enum class Register : uint8_t {
   kReset = 0,
   kRevision = 1,
diff --git a/src/drivers/nvs.cpp b/src/drivers/nvs.cpp
index c2832bf4..7bd1afe2 100644
--- a/src/drivers/nvs.cpp
+++ b/src/drivers/nvs.cpp
@@ -17,6 +17,7 @@
 #include "nvs.h"
 #include "nvs_flash.h"
 #include "tasks.hpp"
+#include "wm8523.hpp"
 
 namespace drivers {
 
@@ -27,6 +28,8 @@ static constexpr char kKeyVersion[] = "ver";
 static constexpr char kKeyBluetooth[] = "bt";
 static constexpr char kKeyOutput[] = "out";
 static constexpr char kKeyBrightness[] = "bright";
+static constexpr char kKeyAmpMaxVolume[] = "hp_vol_max";
+static constexpr char kKeyAmpCurrentVolume[] = "hp_vol";
 
 auto NvsStorage::OpenSync() -> NvsStorage* {
   esp_err_t err = nvs_flash_init();
@@ -154,4 +157,34 @@ auto NvsStorage::ScreenBrightness(uint_fast8_t val) -> std::future<bool> {
   });
 }
 
+auto NvsStorage::AmpMaxVolume() -> std::future<uint16_t> {
+  return writer_->Dispatch<uint16_t>([&]() -> uint16_t {
+    uint16_t out = wm8523::kDefaultMaxVolume;
+    nvs_get_u16(handle_, kKeyAmpMaxVolume, &out);
+    return out;
+  });
+}
+
+auto NvsStorage::AmpMaxVolume(uint16_t val) -> std::future<bool> {
+  return writer_->Dispatch<bool>([&]() {
+    nvs_set_u16(handle_, kKeyAmpMaxVolume, val);
+    return nvs_commit(handle_) == ESP_OK;
+  });
+}
+
+auto NvsStorage::AmpCurrentVolume() -> std::future<uint16_t> {
+  return writer_->Dispatch<uint16_t>([&]() -> uint16_t {
+    uint16_t out = wm8523::kDefaultVolume;
+    nvs_get_u16(handle_, kKeyAmpCurrentVolume, &out);
+    return out;
+  });
+}
+
+auto NvsStorage::AmpCurrentVolume(uint16_t val) -> std::future<bool> {
+  return writer_->Dispatch<bool>([&]() {
+    nvs_set_u16(handle_, kKeyAmpCurrentVolume, val);
+    return nvs_commit(handle_) == ESP_OK;
+  });
+}
+
 }  // namespace drivers
diff --git a/src/drivers/wm8523.cpp b/src/drivers/wm8523.cpp
index e1dffd51..5f6c8053 100644
--- a/src/drivers/wm8523.cpp
+++ b/src/drivers/wm8523.cpp
@@ -15,6 +15,23 @@
 namespace drivers {
 namespace wm8523 {
 
+const uint16_t kAbsoluteMaxVolume = 0x1ff;
+const uint16_t kAbsoluteMinVolume = 0b0;
+
+// This is 3dB below what the DAC considers to be '0dB', and 9.5dB above line
+// level reference.
+const uint16_t kMaxVolumeBeforeClipping = 0x184;
+
+// This is 12.5 dB below what the DAC considers to be '0dB'.
+const uint16_t kLineLevelReferenceVolume = 0x15E;
+
+// Default to -24 dB, which I will claim is 'arbitrarily chosen to be safe but
+// audible', but is in fact just a nice value for my headphones in particular.
+const uint16_t kDefaultVolume = kLineLevelReferenceVolume - 96;
+
+// Default to +6dB == 2Vrms == 'CD Player'
+const uint16_t kDefaultMaxVolume = kLineLevelReferenceVolume + 12;
+
 static const uint8_t kAddress = 0b0011010;
 
 auto ReadRegister(Register reg) -> std::optional<uint16_t> {