68 lines
3 KiB
C++
68 lines
3 KiB
C++
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// firmware/glue/codec_config.hpp — Pure, host-testable translation of a
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// mode's `nisps::DriverConfig` into what the SGTL5000 codec can actually be
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// asked for.
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//
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// Deliberately Arduino-free and memllib-free so `tests/cpp/` can exercise it
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// on the host: this is the only part of the mic/line wiring that has logic in
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// it, and it is the part that can panic the device if it gets the sample rate
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// wrong. `glue/audio_driver.hpp` does the remaining (field-for-field) copy
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// into `AudioDriver::codec_config_t`.
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//
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// Codec limits are read off the vendored driver, not invented:
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// - `AudioControlSGTL5000::lineInLevel` (control_sgtl5000.cpp) clamps to 15;
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// the register is 4 bits per channel.
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// - `AudioControlSGTL5000::micGain` saturates at preamp step 3 (+40 dB) plus
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// input_gain 15, i.e. 40 + ceil(15 * 3 / 2) = 63 dB. Above that the codec
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// setting is identical, so we clamp to the point of saturation.
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// - `AudioDriver::Setup` already truncates output volume above 0.99; it does
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// NOT guard against a negative, which would run through
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// `AudioControlSGTL5000::calcVol` — so clamp both ends here.
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// - `AudioDriver::GetSysClockSpeed` `panic()`s on any sample rate outside
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// {24000, 32000, 44100, 48000}. An engine asking for anything else must
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// NOT brick the boot, so we fall back to 48 kHz.
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#pragma once
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#include <cstdint>
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#include "nisps/core/types.hpp"
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namespace nisps_firmware {
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inline constexpr std::uint8_t kMaxLineLevel = 15u;
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inline constexpr std::uint8_t kMaxMicGainDb = 63u;
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inline constexpr float kMaxOutputVolume = 0.99f;
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inline constexpr std::uint32_t kDefaultSampleRate = 48000u;
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// The rates `AudioDriver::GetSysClockSpeed()` knows a system-clock for.
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inline constexpr std::uint32_t kSupportedSampleRates[] = {
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24000u, 32000u, 44100u, 48000u,
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};
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// Fold a mode's requested config into the codec's representable range.
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// Everything out of range is clamped, never wrapped or ignored.
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inline constexpr nisps::DriverConfig clamp_driver_config(nisps::DriverConfig c) noexcept {
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if (c.line_level > kMaxLineLevel) c.line_level = kMaxLineLevel;
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if (c.mic_gain_db > kMaxMicGainDb) c.mic_gain_db = kMaxMicGainDb;
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if (c.output_volume < 0.f) c.output_volume = 0.f;
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else if (c.output_volume > kMaxOutputVolume) c.output_volume = kMaxOutputVolume;
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return c;
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}
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// Resolve the rate the driver should actually run at.
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// requested <= 0 ⇒ "don't care" ⇒ 48 kHz
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// requested unsupported ⇒ would panic() ⇒ 48 kHz
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// otherwise ⇒ the requested rate
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// Matched with a small tolerance so a float literal like 44100.f that does not
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// round-trip exactly still resolves.
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inline constexpr std::uint32_t select_sample_rate(float requested) noexcept {
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if (!(requested > 0.f)) return kDefaultSampleRate; // also catches NaN
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for (const std::uint32_t rate : kSupportedSampleRates) {
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const float diff = requested - static_cast<float>(rate);
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if (diff > -0.5f && diff < 0.5f) return rate;
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}
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return kDefaultSampleRate;
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}
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} // namespace nisps_firmware
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