OPLL Buffer

#include <opll_buf.h> Buffered access to OPLL registers. More...

Collaboration diagram for OPLL Buffer:

Functions
void	OPLL_init (void)
	MSX Initialize internal buffer for OPLL.
void	OPLL_put (uint8_t reg, uint8_t val)
	MSX Put a pair of OPLL register number and its value to the internal buffer.
void	OPLL_rhythm_mode (bool on)
	MSX Turn RHYTHM mode on/off.
void	OPLL_rhythm (uint8_t val)
	MSX Key-on/off RHYTHM set.
void	OPLL_stop (struct OPLL *opll)
	MSX Stop (Pause) playing sound on OPLL
void	OPLL_play (struct OPLL *opll)
	MSX Play sound on OPLL

Variables
uint8_t	opll_buffer [64]
	MSX Cache of OPLL registers.

Detailed Description

#include <opll_buf.h> Buffered access to OPLL registers.

Provides simple APIs for sound driver developpers.

Example
The following code shows a sound driver/replayer template for the MSX-MUSIC (OPLL).

// -*- coding: utf-8-unix -*-
/*
 * Copyright (c) 2021-2025 Daishi Mori (mori0091)
 *
 * This software is released under the MIT License.\n
 * See https://github.com/mori0091/libmsx/blob/main/LICENSE
 *
 * GitHub libmsx project\n
 * https://github.com/mori0091/libmsx
 */
#include <msx.h>
#include <opll_buf.h>
 
#define LO_BYTE(x) (uint8_t)((x) & 0xff)
#define HI_BYTE(x) (uint8_t)(((x) >> 8) & 0xff)
 
#define SUS_OFF  (0)
#define KEY_OFF  (0)
#define SUS_ON   (uint16_t)(1 << 13)
#define KEY_ON   (uint16_t)(1 << 12)
#define BLOCK(x) (uint16_t)((x) << 9)
#define F_NUM(x) (uint16_t)(x)
 
#define INST(x)  (uint8_t)((x) << 4)
#define VOL(x)   (uint8_t)((x) & 0x0f)
 
 
static struct OPLL opll;
static bool paused;
 
// Initialize the replayer.
void init(void) {
  if (OPLL_find(&opll)) {
    // Enable OPLL.
    // This must be called at least once.
    OPLL_enable(&opll);
 
    // Initialize internal buffer.
    OPLL_init();
 
    // 6 channels + RHYTHM mode
    OPLL_rhythm_mode(true);
  }
}
 
// Main routine of the replayer.
// \note This shall be called every VSYNC timing from interrupt handler.
void play(void) {
  if (!opll.slot) return;
  if (paused) return;
 
  // Apply buffered values to the OPLL registers.
  OPLL_play(&opll);
 
  // Decode one frame of music data and set them to buffers.
  // (Rewrite this block for developping yourown sound driver / replayer)
  {
    static uint8_t t = 0;
 
    // One beat period at 120 bpm.
    const uint8_t len = msx_get_vsync_frequency() * 60 / 120;
 
    if (!t) {
      // ch1 : O4 G, INST=3, VOL=0
      // \note
      // VOL(0) means maximum volume, VOL(15) means minimum volume.
      // VOL(a) means "-3a dB of the maximum volume" (i.e. Vmax * 10^(-0.3a))
      uint16_t x = (SUS_OFF | KEY_ON | BLOCK(4) | F_NUM(257));
      OPLL_put(0x30, (INST(3) | VOL(0)));
      OPLL_put(0x20, HI_BYTE(x));
      OPLL_put(0x10, LO_BYTE(x));
    }
    else if (t == len * 4/5) {
      // ch1: KEY-OFF
      uint16_t x = (SUS_OFF | KEY_OFF | BLOCK(4) | F_NUM(257));
      // OPLL_put(0x30, (INST(3) | VOL(0)));
      OPLL_put(0x20, HI_BYTE(x));
      // OPLL_put(0x10, LO_BYTE(x));
    }
 
    t++;
    if (t == len) {
      t = 0;
    }
  }
}
 
// Start / Resume the replayer.
void start(void) {
  paused = false;
}
 
// Pause the replayer.
void pause(void) {
  paused = true;
  OPLL_stop(&opll);
  __asm__("ei");
}
 
// Return whether the replayer is paused or not.
bool is_paused(void) {
  return paused;
}
 
// Stop the replayer.
void stop(void) {
  pause();
  // Re-initialize internal buffer.
  // (if needed)
  OPLL_init();
}
 
void main(void) {
  // Initialize our replayer.
  init();
  // Set our replayer `play()` to VSYNC handler
  set_vsync_handler(play);
  // Start our replayer.
  start();
 
  uint8_t pressed = false;
  for (;;) {
    await_vsync();
    uint8_t joy = joypad_get_state(0);
    uint8_t clicked = pressed & ~joy;
    pressed = joy;
    if (pressed & (VK_UP | VK_DOWN | VK_LEFT | VK_RIGHT)) {
      // Any of the arrow keys were pressed.
      __asm__("di");
      // All rhythm sets are set to KEY-ON status.
      OPLL_rhythm(0x1f);
      __asm__("ei");
    }
    if (clicked & (VK_UP | VK_DOWN | VK_LEFT | VK_RIGHT)) {
      // Any of the arrow keys were released.
      __asm__("di");
      // All rhythm sets are set to KEY-OFF status.
      OPLL_rhythm(0);
      __asm__("ei");
    }
    if (clicked & VK_FIRE_0) {
      // SPACE key was released.
      if (is_paused()) {
        start();
      }
      else {
        pause();
      }
    }
  }
}

Function Documentation

OPLL_init()

void OPLL_init

(

void

)

MSX Initialize internal buffer for OPLL.

This must be called at least once before OPLL_stop() or OPLL_play().

OPLL_put()

void OPLL_put	(	uint8_t	reg,
		uint8_t	val )

MSX Put a pair of OPLL register number and its value to the internal buffer.

Put the pair of OPLL register #reg and its value val into the internal FIFO buffer. Then, by calling OPLL_play(), all values in the FIFO buffer are written to OPLL.

Parameters

reg	OPLL register number 0x00..0x07 : INSTURUMENT DATA registers 0x0e : RHYTHM control register 0x0f : TEST register 0x10..0x18 : F-Number (LSB 8 bits) registers 0x20..0x28 : SUS/KEY/BLOCK/F-Number (MSB) registers 0x30..0x38 : INSTRUMENT/VOLUME registers
val	a value to be written to the register.

OPLL_rhythm_mode()

void OPLL_rhythm_mode

(

bool

on

)

MSX Turn RHYTHM mode on/off.

Parameters

on	Specify the mode: true : 6 channels + RHYTHM mode. false : 9 channels mode.

OPLL_rhythm()

void OPLL_rhythm

(

uint8_t

val

)

MSX Key-on/off RHYTHM set.

Parameters

val	Key-on/off switch for each RHYTHM set: bit #0 : HH (high-hat) bit #1 : TOP-CY (cymbal) bit #2 : TOM (tom-tom) bit #3 : SD (snare drum) bit #4 : BD (bass drum)

Precondition

The mode shall be 6 channels + RHYTHM mode.

See also

OPLL_rhythm_mode()

OPLL_stop()

void OPLL_stop

(

struct OPLL *

opll

)

MSX Stop (Pause) playing sound on OPLL

Parameters

opll	pointer to the OPLL handle.

Postcondition

Interrupt is disabled.

See also

OPLL_find()

Note

This function simply sets all channels to KEY-OFF.

OPLL_play()

void OPLL_play

(

struct OPLL *

opll

)

MSX Play sound on OPLL

This function applies the values in the internal buffer to OPLL.

Parameters

opll	pointer to the OPLL handle.

Postcondition

Interrupt is disabled.

See also

OPLL_find()

Variable Documentation

opll_buffer

uint8_t opll_buffer[64]

extern

MSX Cache of OPLL registers.

See also

OPLL_put()