Duality/src/sample.c

/*
 * sample.c
 * Duality
 *
 * Copyright (C) 2025 Thomas Buck <thomas@xythobuz.de>
 *
 * Based on examples from gbdk-2020:
 * https://github.com/gbdk-2020/gbdk-2020/tree/develop/gbdk-lib/examples/gb/wav_sample
 *
 * And the docs for the DMG APU:
 * https://gbdev.io/pandocs/Audio_Registers.html
 *
 * 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 3 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.
 *
 * See <http://www.gnu.org/licenses/>.
 */

#include "banks.h"
#include "config.h"
#include "gb/hardware.h"
#include "sfx_shoot.h"
#include "sfx_expl_orb.h"
#include "sfx_expl_ship.h"
#include "sample.h"

BANKREF(sample)

static uint8_t play_bank = 1;
static const uint8_t *play_sample = 0;
static uint16_t play_length = 0;

struct sfxs {
    uint8_t bank;
    uint8_t * const smp;
    uint16_t len;
};

static const struct sfxs sfxs[SFX_COUNT] = {
    { .bank = BANK(sfx_shoot),     .smp = sfx_shoot,     .len = sfx_shoot_SIZE >> 4 },     // SFX_SHOT
    { .bank = BANK(sfx_expl_orb),  .smp = sfx_expl_orb,  .len = sfx_expl_orb_SIZE >> 4 },  // SFX_EXPL_ORB
    { .bank = BANK(sfx_expl_ship), .smp = sfx_expl_ship, .len = sfx_expl_ship_SIZE >> 4 }, // SFX_EXPL_SHIP
};

void sample_play(enum SFXS sfx) BANKED {
    if (sfx >= SFX_COUNT) {
        return;
    }
    if (conf_get()->sfx_vol == 0) {
        return;
    }

    CRITICAL {
        play_bank = sfxs[sfx].bank;
        play_sample = sfxs[sfx].smp;
        play_length = sfxs[sfx].len;
    }
}

uint8_t sample_running(void) BANKED {
    return (play_length > 0) ? 1 : 0;
}

#if 1

// TODO C version has a slight 'beep' always? and much worse at lower volumes?

void sample_isr(void) NONBANKED {
    if (play_length == 0) {
        return;
    }

    NR51_REG = 0xBB; // turn CH3 off in left and right pan
    NR30_REG = 0x00; // turn DAC off

    START_ROM_BANK(play_bank);
        // load waveforms
        for (uint8_t i = 0; i < 16; i++) {
            _AUD3WAVERAM[i] = *(play_sample++);
        }
    END_ROM_BANK();

    NR30_REG = 0x80; // turn DAC on
    NR31_REG = 0xFE; // length of wave, 2nd shortest
    NR32_REG = (4 - conf_get()->sfx_vol) << 5;
    NR33_REG = 0x00; // low freq bits are zero
    NR34_REG = 0xC7; // start, no loop, high freq bits are 111
    NR51_REG = 0xFF; // turn all channels on

    play_length--;
}

#else

// TODO ASM version has less beep at full volume, but also beeping at lower volumes?

void sample_isr(void) NONBANKED NAKED {
    __asm
        ld hl, #_play_length    ; something left to play?
        ld a, (hl+)
        or (hl)
        ret z

        ld hl, #_play_sample
        ld a, (hl+)
        ld h, (hl)
        ld l, a                 ; HL = current position inside the sample

                                ; load new waveform
        ld a, (#__current_bank) ; save bank and switch
        ld e, a
        ld a, (#_play_bank)
        ld (_rROMB0), a

        ldh a, (_NR51_REG)
        ld c, a
        and #0b10111011
        ldh (_NR51_REG), a

        xor a
        ldh (_NR30_REG), a

        .irp ofs,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
            ld a, (hl+)
            ldh (__AUD3WAVERAM+ofs), a
        .endm

        ld a, #0x80
        ldh (_NR30_REG), a
        ld a, #0xFE             ; length of wave
        ldh (_NR31_REG), a
        ld a, #0x20             ; volume
        ldh (_NR32_REG), a
        xor a                   ; low freq bits are zero
        ldh (_NR33_REG), a
        ld a, #0xC7             ; start; no loop; high freq bits are 111
        ldh (_NR34_REG), a

        ld a, c
        ldh (_NR51_REG), a

        ld a, e                 ; restore bank
        ld (_rROMB0), a

        ld a, l                 ; save current position
        ld (#_play_sample), a
        ld a, h
        ld (#_play_sample+1), a

        ld hl, #_play_length    ; decrement length variable
        ld a, (hl)
        sub #1
        ld (hl+), a
        ld a, (hl)
        sbc #0
        ld (hl), a
        ret
    __endasm;
}
#endif