From 000970b770c1951eab412159e5b6d39f5541838f Mon Sep 17 00:00:00 2001
From: rhargreaves <robert@roberthargreaves.net>
Date: Sun, 8 Mar 2020 17:33:52 +0000
Subject: [PATCH] Handle lower limit of PSG frequencies if pitch is shifted
 lower

---
 src/midi_psg.c             | 10 ++++++----
 tests/unit/main.c          |  1 +
 tests/unit/test_midi_psg.c | 19 +++++++++++++++++++
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/midi_psg.c b/src/midi_psg.c
index b6d7247e..0e59fe4f 100644
--- a/src/midi_psg.c
+++ b/src/midi_psg.c
@@ -7,6 +7,7 @@
 #define MIN_PSG_CHAN 6
 #define MAX_PSG_CHAN 9
 #define MIN_MIDI_KEY 45
+#define MAX_MIDI_KEY 127
 #define PITCH_SHIFTS 7
 #define NUM_FREQUENCIES (128 - MIN_MIDI_KEY)
 
@@ -232,10 +233,11 @@ void midi_psg_tick(void)
 
 static u16 freqForMidiKey(u8 midiKey)
 {
-    u8 index = midiKey - MIN_MIDI_KEY;
-    const u8 MAX_INDEX = NUM_FREQUENCIES - 1;
-    if (index > MAX_INDEX) {
-        return FREQUENCIES[MAX_INDEX];
+    if (midiKey < MIN_MIDI_KEY) {
+        return FREQUENCIES[0];
+    }
+    if (midiKey > MAX_MIDI_KEY) {
+        return FREQUENCIES[NUM_FREQUENCIES - 1];
     }
     return FREQUENCIES[midiKey - MIN_MIDI_KEY];
 }
diff --git a/tests/unit/main.c b/tests/unit/main.c
index 84d781c3..44a597dc 100644
--- a/tests/unit/main.c
+++ b/tests/unit/main.c
@@ -79,6 +79,7 @@ int main(void)
             test_midi_psg_envelope_with_loop_end_resets_release_note_after_note_silenced),
         midi_test(test_midi_shifts_semitone_in_psg_envelope),
         midi_test(test_midi_pitch_shift_handles_upper_limit_psg_envelope),
+        midi_test(test_midi_pitch_shift_handles_lower_limit_psg_envelope),
         midi_test(test_midi_channel_volume_sets_volume),
         midi_test(test_midi_pan_sets_synth_stereo_mode_right),
         midi_test(test_midi_pan_sets_synth_stereo_mode_left),
diff --git a/tests/unit/test_midi_psg.c b/tests/unit/test_midi_psg.c
index 28872211..c87b3919 100644
--- a/tests/unit/test_midi_psg.c
+++ b/tests/unit/test_midi_psg.c
@@ -385,3 +385,22 @@ static void test_midi_pitch_shift_handles_upper_limit_psg_envelope(
     expect_psg_attenuation(expectedPsgChan, PSG_ATTENUATION_LOUDEST);
     __real_midi_psg_tick();
 }
+
+static void test_midi_pitch_shift_handles_lower_limit_psg_envelope(
+    UNUSED void** state)
+{
+    const u8 chan = MIN_PSG_CHAN;
+    const u8 expectedPsgChan = 0;
+    const u8 minPitch = 45;
+    const u16 expectedInitialFreq = 0x6e;
+    const u8 envelope[] = { EEF_LOOP_START, 0x00, 0x80, EEF_END };
+    const u8* envelopes[] = { envelope };
+    midi_psg_init(envelopes);
+
+    expect_psg_frequency(expectedPsgChan, expectedInitialFreq);
+    expect_psg_attenuation(expectedPsgChan, PSG_ATTENUATION_LOUDEST);
+    __real_midi_noteOn(chan, minPitch, MAX_MIDI_VOLUME);
+
+    expect_psg_attenuation(expectedPsgChan, PSG_ATTENUATION_LOUDEST);
+    __real_midi_psg_tick();
+}