R4 pre-emptive bringup

Includes stripping out the IC-specific I2S stuff, and doing more manual
volume control using pots

8 files changed, 428 insertions, 683 deletions

diff --git a/src/drivers/CMakeLists.txt b/src/drivers/CMakeLists.txt
index 82acab3d..fff61f5f 100644
--- a/src/drivers/CMakeLists.txt
+++ b/src/drivers/CMakeLists.txt
@@ -3,8 +3,8 @@
 # SPDX-License-Identifier: GPL-3.0-only
 
 idf_component_register(
-  SRCS "touchwheel.cpp" "dac.cpp" "gpio_expander.cpp" "battery.cpp" "storage.cpp" "i2c.cpp"
-  "spi.cpp" "display.cpp" "display_init.cpp" "samd.cpp" "relative_wheel.cpp"
+  SRCS "touchwheel.cpp" "i2s_dac.cpp" "gpio_expander.cpp" "battery.cpp" "storage.cpp" "i2c.cpp"
+  "spi.cpp" "display.cpp" "display_init.cpp" "samd.cpp" "relative_wheel.cpp" "digital_pot.cpp"
   INCLUDE_DIRS "include"
   REQUIRES "esp_adc" "fatfs" "result" "lvgl" "span" "tasks")
 target_compile_options(${COMPONENT_LIB} PRIVATE ${EXTRA_WARNINGS})
diff --git a/src/drivers/dac.cpp b/src/drivers/dac.cpp
deleted file mode 100644
index 3d8e0702..00000000
--- a/src/drivers/dac.cpp
+++ /dev/null
@@ -1,465 +0,0 @@
-/*
- * Copyright 2023 jacqueline <me@jacqueline.id.au>
- *
- * SPDX-License-Identifier: GPL-3.0-only
- */
-
-#include "dac.hpp"
-
-#include <cstdint>
-#include <cstring>
-
-#include "assert.h"
-#include "driver/i2c.h"
-#include "driver/i2s_common.h"
-#include "driver/i2s_std.h"
-#include "esp_attr.h"
-#include "esp_err.h"
-#include "esp_log.h"
-#include "freertos/portmacro.h"
-#include "freertos/projdefs.h"
-#include "hal/gpio_types.h"
-#include "hal/i2c_types.h"
-
-#include "gpio_expander.hpp"
-#include "hal/i2s_types.h"
-#include "i2c.hpp"
-#include "soc/clk_tree_defs.h"
-#include "sys/_stdint.h"
-
-namespace drivers {
-
-static const char* kTag = "AUDIODAC";
-static const uint8_t kPcm5122Address = 0x4C;
-static const i2s_port_t kI2SPort = I2S_NUM_0;
-
-auto AudioDac::create(GpioExpander* expander) -> cpp::result<AudioDac*, Error> {
-  // TODO: tune.
-  i2s_chan_handle_t i2s_handle;
-  i2s_chan_config_t channel_config =
-      I2S_CHANNEL_DEFAULT_CONFIG(kI2SPort, I2S_ROLE_MASTER);
-  // Use the maximum possible DMA buffer size, since a smaller number of large
-  // copies is faster than a large number of small copies.
-  channel_config.dma_frame_num = 1024;
-  // Triple buffering should be enough to keep samples flowing smoothly.
-  // TODO(jacqueline): verify this with 192kHz 32bps.
-  channel_config.dma_desc_num = 4;
-  // channel_config.auto_clear = true;
-
-  ESP_ERROR_CHECK(i2s_new_channel(&channel_config, &i2s_handle, NULL));
-  //
-  // First, instantiate the instance so it can do all of its power on
-  // configuration.
-  std::unique_ptr<AudioDac> dac =
-      std::make_unique<AudioDac>(expander, i2s_handle);
-
-  // Whilst we wait for the initial boot, we can work on installing the I2S
-  // driver.
-  i2s_std_config_t i2s_config = {
-      .clk_cfg = dac->clock_config_,
-      .slot_cfg = dac->slot_config_,
-      .gpio_cfg = {.mclk = GPIO_NUM_0,
-                   .bclk = GPIO_NUM_26,
-                   .ws = GPIO_NUM_27,
-                   .dout = GPIO_NUM_5,
-                   .din = I2S_GPIO_UNUSED,
-                   .invert_flags =
-                       {
-                           .mclk_inv = false,
-                           .bclk_inv = false,
-                           .ws_inv = true,
-                       }},
-  };
-
-  // gpio_set_direction(GPIO_NUM_0, GPIO_MODE_OUTPUT);
-  // gpio_set_level(GPIO_NUM_0, 0);
-
-  if (esp_err_t err =
-          i2s_channel_init_std_mode(i2s_handle, &i2s_config) != ESP_OK) {
-    ESP_LOGE(kTag, "failed to initialise i2s channel %x", err);
-    return cpp::fail(Error::FAILED_TO_INSTALL_I2S);
-  }
-
-  // Make sure the DAC has booted before sending commands to it.
-  bool is_booted = dac->WaitForPowerState(
-      [](bool booted, PowerState state) { return booted; });
-  if (!is_booted) {
-    ESP_LOGE(kTag, "Timed out waiting for boot");
-    return cpp::fail(Error::FAILED_TO_BOOT);
-  }
-
-  // The DAC should be booted but in power down mode, but it might not be if we
-  // didn't shut down cleanly. Reset it to ensure it is in a consistent state.
-  dac->WriteRegister(pcm512x::POWER, 1 << 4);
-  dac->WriteRegister(pcm512x::RESET, 0b10001);
-
-  // Use BCK for the internal PLL.
-  // dac->WriteRegister(Register::PLL_CLOCK_SOURCE, 1 << 4);
-  // dac->WriteRegister(Register::DAC_CLOCK_SOURCE, 0b11 << 5);
-
-  // dac->WriteRegister(Register::PLL_ENABLE, 0);
-  // dac->WriteRegister(Register::DAC_CLOCK_SOURCE, 0b0110000);
-  // dac->WriteRegister(Register::CLOCK_ERRORS, 0b01000001);
-  // dac->WriteRegister(Register::I2S_FORMAT, 0b110000);
-  //  dac->WriteRegister(Register::INTERPOLATION, 1 << 4);
-
-  dac->Reconfigure(BPS_16, SAMPLE_RATE_44_1);
-
-  // Now configure the DAC for standard auto-clock SCK mode.
-
-  // Enable auto clocking, and do your best to carry on despite errors.
-  // dac->WriteRegister(Register::CLOCK_ERRORS, 0b1111101);
-
-  // i2s_channel_enable(dac->i2s_handle_);
-
-  dac->WaitForPowerState([](bool booted, PowerState state) {
-    return state == RUN || state == STANDBY;
-  });
-
-  return dac.release();
-}
-
-AudioDac::AudioDac(GpioExpander* gpio, i2s_chan_handle_t i2s_handle)
-    : gpio_(gpio),
-      i2s_handle_(i2s_handle),
-      i2s_active_(false),
-      active_page_(),
-      clock_config_(I2S_STD_CLK_DEFAULT_CONFIG(44100)),
-      slot_config_(I2S_STD_MSB_SLOT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT,
-                                                   I2S_SLOT_MODE_STEREO)) {
-  clock_config_.clk_src = I2S_CLK_SRC_PLL_160M;
-  gpio_->set_pin(GpioExpander::AMP_EN, true);
-  gpio_->Write();
-}
-
-AudioDac::~AudioDac() {
-  i2s_channel_disable(i2s_handle_);
-  i2s_del_channel(i2s_handle_);
-  gpio_->set_pin(GpioExpander::AMP_EN, false);
-  gpio_->Write();
-}
-
-void AudioDac::WriteVolume(uint8_t volume) {
-  // Left channel.
-  WriteRegister(pcm512x::DIGITAL_VOLUME_2, volume);
-  // Right channel.
-  WriteRegister(pcm512x::DIGITAL_VOLUME_3, volume);
-}
-
-std::pair<bool, AudioDac::PowerState> AudioDac::ReadPowerState() {
-  uint8_t result = ReadRegister(pcm512x::POWER_STATE);
-  bool is_booted = result >> 7;
-  PowerState detail = (PowerState)(result & 0b1111);
-  return std::pair(is_booted, detail);
-}
-
-bool AudioDac::WaitForPowerState(
-    std::function<bool(bool, AudioDac::PowerState)> predicate) {
-  bool has_matched = false;
-  for (int i = 0; i < 10; i++) {
-    std::pair<bool, PowerState> result = ReadPowerState();
-    has_matched = predicate(result.first, result.second);
-    if (has_matched) {
-      break;
-    } else {
-      ESP_LOGI(kTag, "Waiting for power state (was %d 0x%x)", result.first,
-               (uint8_t)result.second);
-      vTaskDelay(pdMS_TO_TICKS(250));
-    }
-  }
-  return has_matched;
-}
-
-auto AudioDac::Reconfigure(BitsPerSample bps, SampleRate rate) -> void {
-  if (i2s_active_) {
-    WriteRegister(pcm512x::MUTE, 0b10001);
-    vTaskDelay(1);
-    WriteRegister(pcm512x::POWER, 1 << 4);
-    i2s_channel_disable(i2s_handle_);
-  }
-
-  // I2S reconfiguration.
-  uint8_t bps_bits = 0;
-  switch (bps) {
-    case BPS_16:
-      slot_config_.data_bit_width = I2S_DATA_BIT_WIDTH_16BIT;
-      bps_bits = 0;
-      break;
-    case BPS_24:
-      slot_config_.data_bit_width = I2S_DATA_BIT_WIDTH_24BIT;
-      bps_bits = 0b10;
-      break;
-    case BPS_32:
-      slot_config_.data_bit_width = I2S_DATA_BIT_WIDTH_32BIT;
-      bps_bits = 0b11;
-      break;
-  }
-  ESP_ERROR_CHECK(i2s_channel_reconfig_std_slot(i2s_handle_, &slot_config_));
-
-  clock_config_.sample_rate_hz = rate;
-  // If we have an MCLK/SCK, then it must be a multiple of both the sample rate
-  // and the bit clock. At 24 BPS, we therefore have to change the MCLK multiple
-  // to avoid issues at some sample rates. (e.g. 48KHz)
-  clock_config_.mclk_multiple =
-      bps == BPS_24 ? I2S_MCLK_MULTIPLE_384 : I2S_MCLK_MULTIPLE_256;
-  ESP_ERROR_CHECK(i2s_channel_reconfig_std_clock(i2s_handle_, &clock_config_));
-
-  // DAC reconfiguration.
-  // Inspired heavily by https://github.com/tommag/PCM51xx_Arduino (MIT).
-
-  // Check that the bit clock (PLL input) is between 1MHz and 50MHz. It always
-  // should be.
-  uint32_t bckFreq = rate * bps * 2;
-  if (bckFreq < 1000000 || bckFreq > 50000000) {
-    ESP_LOGE(kTag, "bck freq out of range");
-    return;
-  }
-
-  // 24 bits is not supported for 44.1kHz and 48kHz.
-  if ((rate == SAMPLE_RATE_44_1 || rate == SAMPLE_RATE_48) && bps == BPS_24) {
-    // TODO(jacqueline): I think this *can* be implemented, but requires a bunch
-    // of maths.
-    ESP_LOGE(kTag, "sample rate and bps mismatch");
-    return;
-  }
-
-  // Initialize system clock from the I2S BCK input
-  //  Disable clock autoset and ignore SCK detection
-  WriteRegister(pcm512x::ERROR_DETECT, 0x1A);
-  // Set PLL clock source to BCK
-  WriteRegister(pcm512x::PLL_REF, 0x10);
-  // Set DAC clock source to PLL output
-  WriteRegister(pcm512x::DAC_REF, 0x10);
-
-  // PLL configuration
-  int p, j, d, r;
-
-  // Clock dividers
-  int nmac, ndac, ncp, dosr, idac;
-
-  if (rate == SAMPLE_RATE_11_025 || rate == SAMPLE_RATE_22_05 ||
-      rate == SAMPLE_RATE_44_1) {
-    // 44.1kHz and derivatives.
-    // P = 1, R = 2, D = 0 for all supported combinations.
-    // Set J to have PLL clk = 90.3168 MHz
-    p = 1;
-    r = 2;
-    j = 90316800 / bckFreq / r;
-    d = 0;
-
-    // Derive clocks from the 90.3168MHz PLL
-    nmac = 2;
-    ndac = 16;
-    ncp = 4;
-    dosr = 8;
-    idac = 1024;  // DSP clock / sample rate
-  } else {
-    // 8kHz and multiples.
-    // PLL config for a 98.304 MHz PLL clk
-    if (bps == BPS_24 && bckFreq > 1536000) {
-      p = 3;
-    } else if (bckFreq > 12288000) {
-      p = 2;
-    } else {
-      p = 1;
-    }
-
-    r = 2;
-    j = 98304000 / (bckFreq / p) / r;
-    d = 0;
-
-    // Derive clocks from the 98.304MHz PLL
-    switch (rate) {
-      case SAMPLE_RATE_16:
-        nmac = 6;
-        break;
-      case SAMPLE_RATE_32:
-        nmac = 3;
-        break;
-      default:
-        nmac = 2;
-        break;
-    }
-
-    ndac = 16;
-    ncp = 4;
-    dosr = 384000 / rate;
-    idac = 98304000 / nmac / rate;  // DSP clock / sample rate
-  }
-
-  // Configure PLL
-  WriteRegister(pcm512x::PLL_COEFF_0, p - 1);
-  WriteRegister(pcm512x::PLL_COEFF_1, j);
-  WriteRegister(pcm512x::PLL_COEFF_2, (d >> 8) & 0x3F);
-  WriteRegister(pcm512x::PLL_COEFF_3, d & 0xFF);
-  WriteRegister(pcm512x::PLL_COEFF_4, r - 1);
-
-  // Clock dividers
-  WriteRegister(pcm512x::DSP_CLKDIV, nmac - 1);
-  WriteRegister(pcm512x::DAC_CLKDIV, ndac - 1);
-  WriteRegister(pcm512x::NCP_CLKDIV, ncp - 1);
-  WriteRegister(pcm512x::OSR_CLKDIV, dosr - 1);
-
-  // IDAC (nb of DSP clock cycles per sample)
-  WriteRegister(pcm512x::IDAC_1, (idac >> 8) & 0xFF);
-  WriteRegister(pcm512x::IDAC_2, idac & 0xFF);
-
-  // FS speed mode
-  int speedMode;
-  if (rate <= SAMPLE_RATE_48) {
-    speedMode = 0;
-  } else if (rate <= SAMPLE_RATE_96) {
-    speedMode = 1;
-  } else if (rate <= SAMPLE_RATE_192) {
-    speedMode = 2;
-  } else {
-    speedMode = 3;
-  }
-  WriteRegister(pcm512x::FS_SPEED_MODE, speedMode);
-
-  WriteRegister(pcm512x::I2S_1, (0b11 << 4) | bps_bits);
-  WriteRegister(pcm512x::I2S_2, 0);
-
-  // Configuration is all done, so we can now bring the DAC and I2S stream back
-  // up. I2S first, since otherwise the DAC will see that there's no clocks and
-  // shut itself down.
-  ESP_ERROR_CHECK(i2s_channel_enable(i2s_handle_));
-  WriteRegister(pcm512x::POWER, 0);
-
-  if (i2s_active_) {
-    vTaskDelay(1);
-    WriteRegister(pcm512x::MUTE, 0);
-  }
-  i2s_active_ = true;
-}
-
-auto AudioDac::WriteData(const cpp::span<const std::byte>& data) -> void {
-  std::size_t bytes_written = 0;
-  esp_err_t err = i2s_channel_write(i2s_handle_, data.data(), data.size_bytes(),
-                                    &bytes_written, portMAX_DELAY);
-  if (err != ESP_ERR_TIMEOUT) {
-    ESP_ERROR_CHECK(err);
-  }
-}
-
-extern "C" IRAM_ATTR auto callback(i2s_chan_handle_t handle,
-                                   i2s_event_data_t* event,
-                                   void* user_ctx) -> bool {
-  if (event == nullptr || user_ctx == nullptr) {
-    return false;
-  }
-  if (event->data == nullptr || event->size == 0) {
-    return false;
-  }
-  uint8_t** buf = reinterpret_cast<uint8_t**>(event->data);
-  StreamBufferHandle_t src = reinterpret_cast<StreamBufferHandle_t>(user_ctx);
-  BaseType_t ret = false;
-  std::size_t bytes_received =
-      xStreamBufferReceiveFromISR(src, *buf, event->size, &ret);
-  if (bytes_received < event->size) {
-    memset(*buf + bytes_received, 0, event->size - bytes_received);
-  }
-  return ret;
-}
-
-auto AudioDac::SetSource(StreamBufferHandle_t buffer) -> void {
-  if (i2s_active_) {
-    ESP_ERROR_CHECK(i2s_channel_disable(i2s_handle_));
-  }
-  i2s_event_callbacks_t callbacks{
-      .on_recv = NULL,
-      .on_recv_q_ovf = NULL,
-      .on_sent = NULL,
-      .on_send_q_ovf = NULL,
-  };
-  if (buffer != nullptr) {
-    callbacks.on_sent = &callback;
-  }
-  i2s_channel_register_event_callback(i2s_handle_, &callbacks, buffer);
-  if (i2s_active_) {
-    ESP_ERROR_CHECK(i2s_channel_enable(i2s_handle_));
-  }
-}
-
-auto AudioDac::Stop() -> void {
-  LogStatus();
-  WriteRegister(pcm512x::POWER, 1 << 4);
-  i2s_channel_disable(i2s_handle_);
-}
-
-#define BYTE_TO_BINARY_PATTERN "%c%c%c%c%c%c%c%c"
-#define BYTE_TO_BINARY(byte)                                \
-  (byte & 0x80 ? '1' : '0'), (byte & 0x40 ? '1' : '0'),     \
-      (byte & 0x20 ? '1' : '0'), (byte & 0x10 ? '1' : '0'), \
-      (byte & 0x08 ? '1' : '0'), (byte & 0x04 ? '1' : '0'), \
-      (byte & 0x02 ? '1' : '0'), (byte & 0x01 ? '1' : '0')
-
-auto AudioDac::LogStatus() -> void {
-  uint8_t res;
-
-  res = ReadRegister(pcm512x::RATE_DET_1);
-  ESP_LOGI(kTag, "detected sample rate (want 3): %u", (res & 0b01110000) >> 4);
-  ESP_LOGI(kTag, "detected SCK ratio (want 6): %u", res && 0b1111);
-
-  res = ReadRegister(pcm512x::RATE_DET_3);
-  ESP_LOGI(kTag, "detected BCK (want... 16? 32?): %u", res);
-
-  res = ReadRegister(pcm512x::RATE_DET_4);
-  ESP_LOGI(kTag, "clock errors (want zeroes): ");
-  ESP_LOGI(kTag, BYTE_TO_BINARY_PATTERN, BYTE_TO_BINARY(res & 0b1111111));
-
-  res = ReadRegister(pcm512x::CLOCK_STATUS);
-  ESP_LOGI(kTag, "clock status (want zeroes): ");
-  ESP_LOGI(kTag, BYTE_TO_BINARY_PATTERN, BYTE_TO_BINARY(res & 0b10111));
-
-  res = ReadRegister(pcm512x::DIGITAL_MUTE_DET);
-  ESP_LOGI(kTag, "automute status (want 0): %u", res & 0b10001);
-
-  auto power = ReadPowerState();
-  ESP_LOGI(kTag, "current power state (want 5): %u", power.second);
-}
-
-void AudioDac::WriteRegister(pcm512x::Register r, uint8_t val) {
-  SelectPage(r.page);
-  WriteRegisterRaw(r.reg, val);
-}
-
-uint8_t AudioDac::ReadRegister(pcm512x::Register r) {
-  SelectPage(r.page);
-  return ReadRegisterRaw(r.reg);
-}
-
-void AudioDac::SelectPage(uint8_t page) {
-  if (active_page_ && active_page_ == page) {
-    return;
-  }
-  WriteRegisterRaw(0, page);
-  active_page_ = page;
-}
-
-void AudioDac::WriteRegisterRaw(uint8_t reg, uint8_t val) {
-  I2CTransaction transaction;
-  transaction.start()
-      .write_addr(kPcm5122Address, I2C_MASTER_WRITE)
-      .write_ack(reg, val)
-      .stop();
-  // TODO: Retry once?
-  transaction.Execute();
-}
-
-uint8_t AudioDac::ReadRegisterRaw(uint8_t reg) {
-  uint8_t result = 0;
-  I2CTransaction transaction;
-  transaction.start()
-      .write_addr(kPcm5122Address, I2C_MASTER_WRITE)
-      .write_ack(reg)
-      .start()
-      .write_addr(kPcm5122Address, I2C_MASTER_READ)
-      .read(&result, I2C_MASTER_NACK)
-      .stop();
-
-  transaction.Execute();
-  return result;
-}
-
-}  // namespace drivers
diff --git a/src/drivers/digital_pot.cpp b/src/drivers/digital_pot.cpp
new file mode 100644
index 00000000..b20d982d
--- /dev/null
+++ b/src/drivers/digital_pot.cpp
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include "digital_pot.hpp"
+
+#include <cstdint>
+
+namespace drivers {
+
+using GpioExpander::VOL_LEFT;
+using GpioExpander::VOL_RIGHT;
+using GpioExpander::VOL_UP_DOWN;
+using GpioExpander::VOL_Z_CROSS;
+
+DigitalPot::DigitalPot(GpioExpander* gpios) : gpios_(gpios) {
+  gpios_->set_pin(VOL_Z_CROSS, true);  // Active-low
+  gpios_->set_pin(VOL_UP_DOWN, true);
+  gpios_->set_pin(VOL_LEFT, false);
+  gpios_->set_pin(VOL_RIGHT, false);
+  gpios_->Write();
+
+  // Power-on reset sets attenuation to maximum anyway, but we want to be safe
+  // and not blow anyone's ears out.
+  for (int i = 0; i < 32; i++) {
+    gpios_->set_pin(VOL_LEFT, true);
+    gpios_->set_pin(VOL_RIGHT, true);
+    gpios_->Write();
+    gpios_->set_pin(VOL_LEFT, false);
+    gpios_->set_pin(VOL_RIGHT, false);
+    gpios_->Write();
+  }
+}
+
+auto DigitalPot::SetRelative(int_fast8_t change) -> void {
+  if (change == 0) {
+    return;
+  }
+
+  gpios_->set_pin(VOL_UP_DOWN, change > 0);
+  gpios_->Write();
+
+  for (int i = 0; i < std::abs(change); i++) {
+    gpios_->set_pin(VOL_LEFT, true);
+    gpios_->set_pin(VOL_RIGHT, true);
+    gpios_->Write();
+    gpios_->set_pin(VOL_LEFT, false);
+    gpios_->set_pin(VOL_RIGHT, false);
+    gpios_->Write();
+  }
+}
+
+auto DigitalPot::SetRelative(Channel ch, int_fast8_t change) -> void {
+  if (change == 0) {
+    return;
+  }
+
+  GpioExpander::Pin pin = (ch == Channel::kLeft) ? VOL_LEFT : VOL_RIGHT;
+  gpios_->set_pin(VOL_UP_DOWN, change > 0);
+  gpios_->Write();
+
+  for (int i = 0; i < std::abs(change); i++) {
+    gpios_->set_pin(pin, true);
+    gpios_->Write();
+    gpios_->set_pin(pin, false);
+    gpios_->Write();
+  }
+}
+
+auto DigitalPot::SetZeroCrossDetect(bool enabled) -> void {
+  gpios_->set_pin(VOL_Z_CROSS, !enabled);  // Active-low
+  gpios_->Write();
+}
+
+auto DigitalPot::GetMaxAttenuation() -> int_fast8_t {
+  return 31;
+}
+
+auto DigitalPot::GetMinAttenuation() -> int_fast8_t {
+  return 0;
+}
+
+}  // namespace drivers
diff --git a/src/drivers/i2s_dac.cpp b/src/drivers/i2s_dac.cpp
new file mode 100644
index 00000000..68e92970
--- /dev/null
+++ b/src/drivers/i2s_dac.cpp
@@ -0,0 +1,202 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include "i2s_dac.hpp"
+
+#include <cstdint>
+#include <cstring>
+
+#include "assert.h"
+#include "driver/i2c.h"
+#include "driver/i2s_common.h"
+#include "driver/i2s_std.h"
+#include "esp_attr.h"
+#include "esp_err.h"
+#include "esp_log.h"
+#include "freertos/portmacro.h"
+#include "freertos/projdefs.h"
+#include "hal/gpio_types.h"
+#include "hal/i2c_types.h"
+
+#include "gpio_expander.hpp"
+#include "hal/i2s_types.h"
+#include "i2c.hpp"
+#include "soc/clk_tree_defs.h"
+#include "sys/_stdint.h"
+
+namespace drivers {
+
+static const char* kTag = "i2s_dac";
+static const i2s_port_t kI2SPort = I2S_NUM_0;
+
+auto I2SDac::create(GpioExpander* expander) -> std::optional<I2SDac*> {
+  i2s_chan_handle_t i2s_handle;
+  i2s_chan_config_t channel_config =
+      I2S_CHANNEL_DEFAULT_CONFIG(kI2SPort, I2S_ROLE_MASTER);
+
+  // Use the maximum possible DMA buffer size, since a smaller number of large
+  // copies is faster than a large number of small copies.
+  channel_config.dma_frame_num = 1024;
+  // Triple buffering should be enough to keep samples flowing smoothly.
+  // TODO(jacqueline): verify this with 192kHz 32bps.
+  channel_config.dma_desc_num = 4;
+  // channel_config.auto_clear = true;
+
+  ESP_ERROR_CHECK(i2s_new_channel(&channel_config, &i2s_handle, NULL));
+  //
+  // First, instantiate the instance so it can do all of its power on
+  // configuration.
+  std::unique_ptr<I2SDac> dac = std::make_unique<I2SDac>(expander, i2s_handle);
+
+  // Whilst we wait for the initial boot, we can work on installing the I2S
+  // driver.
+  i2s_std_config_t i2s_config = {
+      .clk_cfg = dac->clock_config_,
+      .slot_cfg = dac->slot_config_,
+      .gpio_cfg = {.mclk = GPIO_NUM_0,
+                   .bclk = GPIO_NUM_26,
+                   .ws = GPIO_NUM_27,
+                   .dout = GPIO_NUM_5,
+                   .din = I2S_GPIO_UNUSED,
+                   .invert_flags =
+                       {
+                           .mclk_inv = false,
+                           .bclk_inv = false,
+                           .ws_inv = true,
+                       }},
+  };
+
+  if (esp_err_t err =
+          i2s_channel_init_std_mode(i2s_handle, &i2s_config) != ESP_OK) {
+    ESP_LOGE(kTag, "failed to initialise i2s channel %x", err);
+    return {};
+  }
+
+  return dac.release();
+}
+
+I2SDac::I2SDac(GpioExpander* gpio, i2s_chan_handle_t i2s_handle)
+    : gpio_(gpio),
+      i2s_handle_(i2s_handle),
+      i2s_active_(false),
+      active_page_(),
+      clock_config_(I2S_STD_CLK_DEFAULT_CONFIG(44100)),
+      slot_config_(I2S_STD_MSB_SLOT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT,
+                                                   I2S_SLOT_MODE_STEREO)) {
+  clock_config_.clk_src = I2S_CLK_SRC_PLL_160M;
+  gpio_->set_pin(GpioExpander::AMP_EN, false);
+  gpio_->Write();
+}
+
+I2SDac::~I2SDac() {
+  Stop();
+  i2s_del_channel(i2s_handle_);
+}
+
+auto I2SDac::Start() -> void {
+  gpio_->set_pin(GpioExpander::AMP_EN, true);
+  gpio_->Write();
+
+  vTaskDelay(pdMS_TO_TICKS(1));
+  i2s_channel_enable(i2s_handle_);
+
+  i2s_active_ = true;
+}
+
+auto I2SDac::Stop() -> void {
+  i2s_channel_disable(i2s_handle_);
+  vTaskDelay(pdMS_TO_TICKS(1));
+
+  gpio_->set_pin(GpioExpander::AMP_EN, false);
+  gpio_->Write();
+
+  i2s_active_ = false;
+}
+
+auto I2SDac::Reconfigure(BitsPerSample bps, SampleRate rate) -> void {
+  if (i2s_active_) {
+    i2s_channel_disable(i2s_handle_);
+  }
+
+  uint8_t bps_bits = 0;
+  switch (bps) {
+    case BPS_16:
+      slot_config_.data_bit_width = I2S_DATA_BIT_WIDTH_16BIT;
+      bps_bits = 0;
+      break;
+    case BPS_24:
+      slot_config_.data_bit_width = I2S_DATA_BIT_WIDTH_24BIT;
+      bps_bits = 0b10;
+      break;
+    case BPS_32:
+      slot_config_.data_bit_width = I2S_DATA_BIT_WIDTH_32BIT;
+      bps_bits = 0b11;
+      break;
+  }
+  ESP_ERROR_CHECK(i2s_channel_reconfig_std_slot(i2s_handle_, &slot_config_));
+
+  clock_config_.sample_rate_hz = rate;
+  // If we have an MCLK/SCK, then it must be a multiple of both the sample rate
+  // and the bit clock. At 24 BPS, we therefore have to change the MCLK multiple
+  // to avoid issues at some sample rates. (e.g. 48KHz)
+  clock_config_.mclk_multiple =
+      bps == BPS_24 ? I2S_MCLK_MULTIPLE_384 : I2S_MCLK_MULTIPLE_256;
+  ESP_ERROR_CHECK(i2s_channel_reconfig_std_clock(i2s_handle_, &clock_config_));
+
+  if (i2s_active_) {
+    i2s_channel_enable(i2s_handle_);
+  }
+}
+
+auto I2SDac::WriteData(const cpp::span<const std::byte>& data) -> void {
+  std::size_t bytes_written = 0;
+  esp_err_t err = i2s_channel_write(i2s_handle_, data.data(), data.size_bytes(),
+                                    &bytes_written, portMAX_DELAY);
+  if (err != ESP_ERR_TIMEOUT) {
+    ESP_ERROR_CHECK(err);
+  }
+}
+
+extern "C" IRAM_ATTR auto callback(i2s_chan_handle_t handle,
+                                   i2s_event_data_t* event,
+                                   void* user_ctx) -> bool {
+  if (event == nullptr || user_ctx == nullptr) {
+    return false;
+  }
+  if (event->data == nullptr || event->size == 0) {
+    return false;
+  }
+  uint8_t** buf = reinterpret_cast<uint8_t**>(event->data);
+  StreamBufferHandle_t src = reinterpret_cast<StreamBufferHandle_t>(user_ctx);
+  BaseType_t ret = false;
+  std::size_t bytes_received =
+      xStreamBufferReceiveFromISR(src, *buf, event->size, &ret);
+  if (bytes_received < event->size) {
+    memset(*buf + bytes_received, 0, event->size - bytes_received);
+  }
+  return ret;
+}
+
+auto I2SDac::SetSource(StreamBufferHandle_t buffer) -> void {
+  if (i2s_active_) {
+    ESP_ERROR_CHECK(i2s_channel_disable(i2s_handle_));
+  }
+  i2s_event_callbacks_t callbacks{
+      .on_recv = NULL,
+      .on_recv_q_ovf = NULL,
+      .on_sent = NULL,
+      .on_send_q_ovf = NULL,
+  };
+  if (buffer != nullptr) {
+    callbacks.on_sent = &callback;
+  }
+  i2s_channel_register_event_callback(i2s_handle_, &callbacks, buffer);
+  if (i2s_active_) {
+    ESP_ERROR_CHECK(i2s_channel_enable(i2s_handle_));
+  }
+}
+
+}  // namespace drivers
diff --git a/src/drivers/include/dac.hpp b/src/drivers/include/dac.hpp
deleted file mode 100644
index 22d6c855..00000000
--- a/src/drivers/include/dac.hpp
+++ /dev/null
@@ -1,204 +0,0 @@
-/*
- * Copyright 2023 jacqueline <me@jacqueline.id.au>
- *
- * SPDX-License-Identifier: GPL-3.0-only
- */
-
-#pragma once
-
-#include <stdint.h>
-
-#include <functional>
-#include <memory>
-#include <optional>
-#include <utility>
-
-#include "driver/i2s_std.h"
-#include "driver/i2s_types.h"
-#include "esp_err.h"
-#include "freertos/FreeRTOS.h"
-#include "freertos/portmacro.h"
-#include "freertos/stream_buffer.h"
-#include "result.hpp"
-#include "span.hpp"
-
-#include "gpio_expander.hpp"
-#include "sys/_stdint.h"
-
-namespace drivers {
-
-namespace pcm512x {
-class Register {
- public:
-  uint8_t page;
-  uint8_t reg;
-
-  constexpr Register(uint8_t p, uint8_t r) : page(p), reg(r) {}
-};
-
-constexpr Register RESET(0, 1);
-constexpr Register POWER(0, 2);
-constexpr Register MUTE(0, 3);
-constexpr Register PLL_EN(0, 4);
-constexpr Register SPI_MISO_FUNCTION(0, 6);
-constexpr Register DSP(0, 7);
-constexpr Register GPIO_EN(0, 8);
-constexpr Register BCLK_LRCLK_CFG(0, 9);
-constexpr Register DSP_GPIO_INPUT(0, 10);
-constexpr Register MASTER_MODE(0, 12);
-constexpr Register PLL_REF(0, 13);
-constexpr Register DAC_REF(0, 14);
-constexpr Register GPIO_DACIN(0, 16);
-constexpr Register GPIO_PLLIN(0, 18);
-constexpr Register SYNCHRONIZE(0, 19);
-constexpr Register PLL_COEFF_0(0, 20);
-constexpr Register PLL_COEFF_1(0, 21);
-constexpr Register PLL_COEFF_2(0, 22);
-constexpr Register PLL_COEFF_3(0, 23);
-constexpr Register PLL_COEFF_4(0, 24);
-constexpr Register DSP_CLKDIV(0, 27);
-constexpr Register DAC_CLKDIV(0, 28);
-constexpr Register NCP_CLKDIV(0, 29);
-constexpr Register OSR_CLKDIV(0, 30);
-constexpr Register MASTER_CLKDIV_1(0, 32);
-constexpr Register MASTER_CLKDIV_2(0, 33);
-constexpr Register FS_SPEED_MODE(0, 34);
-constexpr Register IDAC_1(0, 35);
-constexpr Register IDAC_2(0, 36);
-constexpr Register ERROR_DETECT(0, 37);
-constexpr Register I2S_1(0, 40);
-constexpr Register I2S_2(0, 41);
-constexpr Register DAC_ROUTING(0, 42);
-constexpr Register DSP_PROGRAM(0, 43);
-constexpr Register CLKDET(0, 44);
-constexpr Register AUTO_MUTE(0, 59);
-constexpr Register DIGITAL_VOLUME_1(0, 60);
-constexpr Register DIGITAL_VOLUME_2(0, 61);
-constexpr Register DIGITAL_VOLUME_3(0, 62);
-constexpr Register DIGITAL_MUTE_1(0, 63);
-constexpr Register DIGITAL_MUTE_2(0, 64);
-constexpr Register DIGITAL_MUTE_3(0, 65);
-constexpr Register GPIO_OUTPUT_1(0, 80);
-constexpr Register GPIO_OUTPUT_2(0, 81);
-constexpr Register GPIO_OUTPUT_3(0, 82);
-constexpr Register GPIO_OUTPUT_4(0, 83);
-constexpr Register GPIO_OUTPUT_5(0, 84);
-constexpr Register GPIO_OUTPUT_6(0, 85);
-constexpr Register GPIO_CONTROL_1(0, 86);
-constexpr Register GPIO_CONTROL_2(0, 87);
-constexpr Register OVERFLOW(0, 90);
-constexpr Register RATE_DET_1(0, 91);
-constexpr Register RATE_DET_2(0, 92);
-constexpr Register RATE_DET_3(0, 93);
-constexpr Register RATE_DET_4(0, 94);
-constexpr Register CLOCK_STATUS(0, 95);
-constexpr Register ANALOG_MUTE_DET(0, 108);
-constexpr Register POWER_STATE(0, 118);
-constexpr Register GPIN(0, 119);
-constexpr Register DIGITAL_MUTE_DET(0, 120);
-
-constexpr Register OUTPUT_AMPLITUDE(1, 1);
-constexpr Register ANALOG_GAIN_CTRL(1, 2);
-constexpr Register UNDERVOLTAGE_PROT(1, 5);
-constexpr Register ANALOG_MUTE_CTRL(1, 6);
-constexpr Register ANALOG_GAIN_BOOST(1, 7);
-constexpr Register VCOM_CTRL_1(1, 8);
-constexpr Register VCOM_CTRL_2(1, 9);
-
-constexpr Register CRAM_CTRL(44, 1);
-
-constexpr Register FLEX_A(253, 63);
-constexpr Register FLEX_B(253, 64);
-
-}  // namespace pcm512x
-
-/**
- * Interface for a PCM5122PWR DAC, configured over I2C.
- */
-class AudioDac {
- public:
-  enum Error {
-    FAILED_TO_BOOT,
-    FAILED_TO_CONFIGURE,
-    FAILED_TO_INSTALL_I2S,
-  };
-
-  static auto create(GpioExpander* expander) -> cpp::result<AudioDac*, Error>;
-
-  AudioDac(GpioExpander* gpio, i2s_chan_handle_t i2s_handle);
-  ~AudioDac();
-
-  /**
-   * Sets the volume on a scale from 0 (loudest) to 254 (quietest). A value of
-   * 255 engages the soft mute function.
-   */
-  void WriteVolume(uint8_t volume);
-
-  enum PowerState {
-    POWERDOWN = 0b0,
-    WAIT_FOR_CP = 0b1,
-    CALIBRATION_1 = 0b10,
-    CALIBRATION_2 = 0b11,
-    RAMP_UP = 0b100,
-    RUN = 0b101,
-    SHORT = 0b110,
-    RAMP_DOWN = 0b111,
-    STANDBY = 0b1000,
-  };
-
-  /* Returns the current boot-up status and internal state of the DAC */
-  std::pair<bool, PowerState> ReadPowerState();
-
-  enum BitsPerSample {
-    BPS_16 = I2S_DATA_BIT_WIDTH_16BIT,
-    BPS_24 = I2S_DATA_BIT_WIDTH_24BIT,
-    BPS_32 = I2S_DATA_BIT_WIDTH_32BIT,
-  };
-  enum SampleRate {
-    SAMPLE_RATE_11_025 = 11025,
-    SAMPLE_RATE_16 = 16000,
-    SAMPLE_RATE_22_05 = 22050,
-    SAMPLE_RATE_32 = 32000,
-    SAMPLE_RATE_44_1 = 44100,
-    SAMPLE_RATE_48 = 48000,
-    SAMPLE_RATE_96 = 96000,
-    SAMPLE_RATE_192 = 192000,
-  };
-
-  // TODO(jacqueline): worth supporting channels here as well?
-  auto Reconfigure(BitsPerSample bps, SampleRate rate) -> void;
-
-  auto WriteData(const cpp::span<const std::byte>& data) -> void;
-  auto SetSource(StreamBufferHandle_t buffer) -> void;
-
-  auto Stop() -> void;
-  auto LogStatus() -> void;
-
-  // Not copyable or movable.
-  AudioDac(const AudioDac&) = delete;
-  AudioDac& operator=(const AudioDac&) = delete;
-
- private:
-  GpioExpander* gpio_;
-  i2s_chan_handle_t i2s_handle_;
-  bool i2s_active_;
-  std::optional<uint8_t> active_page_;
-
-  i2s_std_clk_config_t clock_config_;
-  i2s_std_slot_config_t slot_config_;
-
-  /*
-   * Pools the power state for up to 10ms, waiting for the given predicate to
-   * be true.
-   */
-  bool WaitForPowerState(std::function<bool(bool, PowerState)> predicate);
-
-  void WriteRegister(pcm512x::Register r, uint8_t val);
-  uint8_t ReadRegister(pcm512x::Register r);
-
-  void SelectPage(uint8_t page);
-  void WriteRegisterRaw(uint8_t reg, uint8_t val);
-  uint8_t ReadRegisterRaw(uint8_t reg);
-};
-
-}  // namespace drivers
diff --git a/src/drivers/include/digital_pot.hpp b/src/drivers/include/digital_pot.hpp
new file mode 100644
index 00000000..e2ca00b1
--- /dev/null
+++ b/src/drivers/include/digital_pot.hpp
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <functional>
+
+#include "esp_err.h"
+#include "result.hpp"
+
+#include "gpio_expander.hpp"
+
+namespace drivers {
+
+/*
+ * Driver for a two-channel digital potentiometer, with steps measured in
+ * decibels.
+ */
+class DigitalPot {
+ public:
+  explicit DigitalPot(GpioExpander* gpios);
+  ~DigitalPot() {}
+
+  // Not copyable or movable.
+  DigitalPot(const DigitalPot&) = delete;
+  DigitalPot& operator=(const DigitalPot&) = delete;
+
+  enum class Channel {
+    kLeft,
+    kRight,
+  };
+
+  auto SetRelative(int_fast8_t change) -> void;
+  auto SetRelative(Channel ch, int_fast8_t change) -> void;
+
+  auto SetZeroCrossDetect(bool enabled) -> void;
+
+  auto GetMaxAttenuation() -> int_fast8_t;
+  auto GetMinAttenuation() -> int_fast8_t;
+
+ private:
+  GpioExpander* gpios_;
+};
+
+}  // namespace drivers
diff --git a/src/drivers/include/gpio_expander.hpp b/src/drivers/include/gpio_expander.hpp
index da682848..8231e140 100644
--- a/src/drivers/include/gpio_expander.hpp
+++ b/src/drivers/include/gpio_expander.hpp
@@ -56,12 +56,12 @@ class GpioExpander {
   static const uint8_t kPortADefault = 0b10111110;
 
   // Port B:
-  // 0 - trs output enable
-  // 1 - 3.5mm jack detect (active low)
-  // 2 - NC
-  // 3 - NC
-  // 4 - NC
-  // 5 - NC
+  // 0 - 3.5mm jack detect (active low)
+  // 1 - trs output enable
+  // 2 - volume zero-cross detection
+  // 3 - volume direction
+  // 4 - volume left channel
+  // 5 - volume right channel
   // 6 - NC
   // 7 - NC
   // Default input high, trs output low
@@ -118,12 +118,12 @@ class GpioExpander {
     SD_CARD_POWER_ENABLE = 7,
 
     // Port B
-    AMP_EN = 8,
-    PHONE_DETECT = 9,
-    // UNUSED = 10,
-    // UNUSED = 11,
-    // UNUSED = 12,
-    // UNUSED = 13,
+    PHONE_DETECT = 8,
+    AMP_EN = 9,
+    VOL_Z_CROSS = 10,
+    VOL_UP_DOWN = 11,
+    VOL_LEFT = 12,
+    VOL_RIGHT = 13,
     // UNUSED = 14,
     // UNUSED = 15,
   };
diff --git a/src/drivers/include/i2s_dac.hpp b/src/drivers/include/i2s_dac.hpp
new file mode 100644
index 00000000..42c094b1
--- /dev/null
+++ b/src/drivers/include/i2s_dac.hpp
@@ -0,0 +1,78 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#include <functional>
+#include <memory>
+#include <optional>
+#include <utility>
+
+#include "driver/i2s_std.h"
+#include "driver/i2s_types.h"
+#include "esp_err.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/portmacro.h"
+#include "freertos/stream_buffer.h"
+#include "result.hpp"
+#include "span.hpp"
+
+#include "gpio_expander.hpp"
+#include "sys/_stdint.h"
+
+namespace drivers {
+
+/**
+ * Interface for a DAC that receives PCM samples over I2S.
+ */
+class I2SDac {
+ public:
+  static auto create(GpioExpander* expander) -> std::optional<I2SDac*>;
+
+  I2SDac(GpioExpander* gpio, i2s_chan_handle_t i2s_handle);
+  ~I2SDac();
+
+  auto Start() -> void;
+  auto Stop() -> void;
+
+  enum BitsPerSample {
+    BPS_16 = I2S_DATA_BIT_WIDTH_16BIT,
+    BPS_24 = I2S_DATA_BIT_WIDTH_24BIT,
+    BPS_32 = I2S_DATA_BIT_WIDTH_32BIT,
+  };
+  enum SampleRate {
+    SAMPLE_RATE_11_025 = 11025,
+    SAMPLE_RATE_16 = 16000,
+    SAMPLE_RATE_22_05 = 22050,
+    SAMPLE_RATE_32 = 32000,
+    SAMPLE_RATE_44_1 = 44100,
+    SAMPLE_RATE_48 = 48000,
+    SAMPLE_RATE_96 = 96000,
+    SAMPLE_RATE_192 = 192000,
+  };
+
+  auto Reconfigure(BitsPerSample bps, SampleRate rate) -> void;
+
+  auto WriteData(const cpp::span<const std::byte>& data) -> void;
+  auto SetSource(StreamBufferHandle_t buffer) -> void;
+
+  // Not copyable or movable.
+  I2SDac(const I2SDac&) = delete;
+  I2SDac& operator=(const I2SDac&) = delete;
+
+ private:
+  GpioExpander* gpio_;
+  i2s_chan_handle_t i2s_handle_;
+  bool i2s_active_;
+  std::optional<uint8_t> active_page_;
+
+  i2s_std_clk_config_t clock_config_;
+  i2s_std_slot_config_t slot_config_;
+};
+
+}  // namespace drivers