git.y1.nz

commit 11ba1df7a3a0a5c15f25ee11714a6fbb397d8a48
parent c50fdfd222ac5a2e07cf9c6f43c645e2dbe0a62d
Author: Lior Halphon <LIJI32@gmail.com>
Date:   Sun, 30 Nov 2025 21:29:37 +0200

NRx4 changing the volume envelope while retaining a sample is only applicable to channels 1 and 2, not 4

Diffstat:
M
Core/apu.c
13
++-----------

1 file changed, 2 insertions(+), 11 deletions(-)
diff --git a/Core/apu.c b/Core/apu.c
@@ -1508,7 +1508,7 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
                     gb->apu.square_channels[index].sample_countdown = (gb->apu.square_channels[index].sample_length ^ 0x7FF) * 2 + gb->apu.square_channels[index].delay;
                 }
                 gb->apu.square_channels[index].current_volume = gb->io_registers[index == GB_SQUARE_1 ? GB_IO_NR12 : GB_IO_NR22] >> 4;
-                /* The volume changes caused by NRX4 sound start take effect instantly (i.e. the effect the previously
+                /* The volume changes caused by NRx4 sound start takes effect instantly (i.e. the effect the previously
                    started sound). The playback itself is not instant which is why we don't update the sample for other
                    cases. */
                 if (gb->apu.is_active[index]) {
@@ -1797,20 +1797,11 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
    
                     gb->apu.noise_channel.current_volume = gb->io_registers[GB_IO_NR42] >> 4;
 
-                    /* The volume changes caused by NRX4 sound start take effect instantly (i.e. the effect the previously
-                     started sound). The playback itself is not instant which is why we don't update the sample for other
-                     cases. */
-                    if (gb->apu.is_active[GB_NOISE]) {
-                        update_sample(gb, GB_NOISE,
-                                      gb->apu.noise_channel.current_lfsr_sample ?
-                                      gb->apu.noise_channel.current_volume : 0,
-                                      0);
-                    }
                     gb->apu.noise_channel.lfsr = 0;
                     gb->apu.noise_channel.current_lfsr_sample = false;
                     gb->apu.noise_channel.volume_countdown = gb->io_registers[GB_IO_NR42] & 7;
 
-                    if (!gb->apu.is_active[GB_NOISE] && (gb->io_registers[GB_IO_NR42] & 0xF8) != 0) {
+                    if (gb->io_registers[GB_IO_NR42] & 0xF8) {
                         gb->apu.is_active[GB_NOISE] = true;
                         update_sample(gb, GB_NOISE, 0, 0);
                     }

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