[Core] Simplify audio_duration_to_ms() and audio_ms_to_duration(), reduce firmware size by a few bytes. (#21427)

6 files changed, 220 insertions, 13 deletions

diff --git a/platforms/test/drivers/audio_pwm.h b/platforms/test/drivers/audio_pwm.h
new file mode 100644
index 0000000000..9a3fa88cec
--- /dev/null
+++ b/platforms/test/drivers/audio_pwm.h
@@ -0,0 +1,16 @@
+// Copyright 2023 Google LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#pragma once
diff --git a/platforms/test/drivers/audio_pwm_hardware.c b/platforms/test/drivers/audio_pwm_hardware.c
new file mode 100644
index 0000000000..336e4f5844
--- /dev/null
+++ b/platforms/test/drivers/audio_pwm_hardware.c
@@ -0,0 +1,20 @@
+// Copyright 2023 Google LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include "audio.h"
+
+void audio_driver_initialize(void) {}
+void audio_driver_start() {}
+void audio_driver_stop() {}
diff --git a/quantum/audio/audio.c b/quantum/audio/audio.c
index 2570ad9cd1..0300483a93 100644
--- a/quantum/audio/audio.c
+++ b/quantum/audio/audio.c
@@ -547,20 +547,39 @@ void audio_decrease_tempo(uint8_t tempo_change) {
         note_tempo -= tempo_change;
 }
 
-// TODO in the int-math version are some bugs; songs sometimes abruptly end - maybe an issue with the timer/system-tick wrapping around?
+/**
+ * Converts from units of 1/64ths of a beat to milliseconds.
+ *
+ * Round-off error is at most 1 millisecond.
+ *
+ * Conversion will never overflow for duration_bpm <= 699, provided that
+ * note_tempo is at least 10. This is quite a long duration, over ten beats.
+ *
+ * Beware that for duration_bpm > 699, the result may overflow uint16_t range
+ * when duration_bpm is large compared to note_tempo:
+ *
+ *    duration_bpm * 60 * 1000 / (64 * note_tempo) > UINT16_MAX
+ *
+ *    duration_bpm > (2 * 65535 / 1875) * note_tempo
+ *                 = 69.904 * note_tempo.
+ */
 uint16_t audio_duration_to_ms(uint16_t duration_bpm) {
-#if defined(__AVR__)
-    // doing int-math saves us some bytes in the overall firmware size, but the intermediate result is less accurate before being cast to/returned as uint
-    return ((uint32_t)duration_bpm * 60 * 1000) / (64 * note_tempo);
-    // NOTE: beware of uint16_t overflows when note_tempo is low and/or the duration is long
-#else
-    return ((float)duration_bpm * 60) / (64 * note_tempo) * 1000;
-#endif
+    return ((uint32_t)duration_bpm * 1875) / ((uint_fast16_t)note_tempo * 2);
 }
+
+/**
+ * Converts from units of milliseconds to 1/64ths of a beat.
+ *
+ * Round-off error is at most 1/64th of a beat.
+ *
+ * This conversion never overflows: since duration_ms <= UINT16_MAX = 65535
+ * and note_tempo <= 255, the result is always in uint16_t range:
+ *
+ *     duration_ms * 64 * note_tempo / 60 / 1000
+ *     <= 65535 * 2 * 255 / 1875
+ *      = 17825.52
+ *     <= UINT16_MAX.
+ */
 uint16_t audio_ms_to_duration(uint16_t duration_ms) {
-#if defined(__AVR__)
-    return ((uint32_t)duration_ms * 64 * note_tempo) / 60 / 1000;
-#else
-    return ((float)duration_ms * 64 * note_tempo) / 60 / 1000;
-#endif
+    return ((uint32_t)duration_ms * 2 * note_tempo) / 1875;
 }
diff --git a/tests/audio/config.h b/tests/audio/config.h
new file mode 100644
index 0000000000..d0c4ddadbd
--- /dev/null
+++ b/tests/audio/config.h
@@ -0,0 +1,18 @@
+// Copyright 2023 Google LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include "test_common.h"
diff --git a/tests/audio/test.mk b/tests/audio/test.mk
new file mode 100644
index 0000000000..a2c71d9587
--- /dev/null
+++ b/tests/audio/test.mk
@@ -0,0 +1,16 @@
+# Copyright 2023 Google LLC
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+AUDIO_ENABLE = yes
diff --git a/tests/audio/test_audio.cpp b/tests/audio/test_audio.cpp
new file mode 100644
index 0000000000..ef34748b06
--- /dev/null
+++ b/tests/audio/test_audio.cpp
@@ -0,0 +1,118 @@
+// Copyright 2023 Google LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include <cmath>
+#include <random>
+
+#include "gtest/gtest.h"
+#include "keyboard_report_util.hpp"
+#include "test_common.hpp"
+
+namespace {
+
+class AudioTest : public TestFixture {
+   public:
+    uint16_t infer_tempo() {
+        return audio_ms_to_duration(1875) / 2;
+    }
+};
+
+TEST_F(AudioTest, OnOffToggle) {
+    audio_on();
+    EXPECT_TRUE(audio_is_on());
+
+    audio_off();
+    EXPECT_FALSE(audio_is_on());
+
+    audio_toggle();
+    EXPECT_TRUE(audio_is_on());
+
+    audio_toggle();
+    EXPECT_FALSE(audio_is_on());
+}
+
+TEST_F(AudioTest, ChangeTempo) {
+    for (int tempo = 50; tempo <= 250; tempo += 50) {
+        audio_set_tempo(tempo);
+        EXPECT_EQ(infer_tempo(), tempo);
+    }
+
+    audio_set_tempo(10);
+    audio_increase_tempo(25);
+    EXPECT_EQ(infer_tempo(), 35);
+
+    audio_decrease_tempo(4);
+    EXPECT_EQ(infer_tempo(), 31);
+
+    audio_increase_tempo(250);
+    EXPECT_EQ(infer_tempo(), 255);
+
+    audio_set_tempo(9);
+    EXPECT_EQ(infer_tempo(), 10);
+
+    audio_decrease_tempo(100);
+    EXPECT_EQ(infer_tempo(), 10);
+}
+
+TEST_F(AudioTest, BpmConversion) {
+    const int tol = 1;
+
+    audio_set_tempo(120);
+    // At 120 bpm, there are 2 beats per second, and a whole note is 500 ms.
+    EXPECT_NEAR(audio_duration_to_ms(64 /* whole note */), 500, tol);
+    EXPECT_NEAR(audio_ms_to_duration(500), 64, tol);
+    EXPECT_EQ(audio_duration_to_ms(0), 0);
+    EXPECT_EQ(audio_ms_to_duration(0), 0);
+
+    audio_set_tempo(10);
+    // At 10 bpm, UINT16_MAX ms corresponds to 699/64 beats and is the longest
+    // duration that can be converted without overflow.
+    EXPECT_NEAR(audio_ms_to_duration(UINT16_MAX), 699, tol);
+    EXPECT_NEAR(audio_duration_to_ms(699), 65531, tol);
+
+    audio_set_tempo(255);
+    // At 255 bpm, UINT16_MAX ms corresponds to 17825/64 beats and is the longest
+    // duration that can be converted without overflow.
+    EXPECT_NEAR(audio_ms_to_duration(UINT16_MAX), 17825, tol);
+    EXPECT_NEAR(audio_duration_to_ms(17825), 65533, tol);
+
+    std::mt19937                       rng(0 /*seed*/);
+    std::uniform_int_distribution<int> dist_tempo(10, 255);
+    std::uniform_int_distribution<int> dist_ms(0, UINT16_MAX);
+
+    // Test bpm <-> ms conversions for random tempos and durations.
+    for (int trial = 0; trial < 50; ++trial) {
+        const int tempo       = dist_tempo(rng);
+        const int duration_ms = dist_ms(rng);
+        SCOPED_TRACE("tempo " + testing::PrintToString(tempo) + ", duration " + testing::PrintToString(duration_ms) + " ms");
+
+        audio_set_tempo(tempo);
+        int duration_bpm = std::round((64.0f / (60.0f * 1000.0f)) * duration_ms * tempo);
+        ASSERT_NEAR(audio_ms_to_duration(duration_ms), duration_bpm, tol);
+
+        int roundtrip_ms = std::round((60.0f * 1000.0f / 64.0f) * duration_bpm / tempo);
+        // Because of round-off error, duration_ms and roundtrip_ms may differ by
+        // about (60 * 1000 / 64) / tempo.
+        int roundtrip_tol = tol * (60.0f * 1000.0f / 64.0f) / tempo;
+        ASSERT_NEAR(roundtrip_ms, duration_ms, roundtrip_tol);
+
+        // Only test converting back to ms if the result would be in uint16_t range.
+        if (roundtrip_ms <= UINT16_MAX) {
+            ASSERT_NEAR(audio_duration_to_ms(duration_bpm), roundtrip_ms, tol);
+        }
+    }
+}
+
+} // namespace