chips/pmdwin/psg.c

/* FIXME: move ugly-ass legalese somewhere where it won't be seen
// by anyone other than lawyers. (/dev/null would be ideal but sadly
// we live in an imperfect world). */
/* Copyright (c) 2012/2013, Peter Barfuss
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/* Quick, somewhat hacky PSG implementation. Seems to work fine in most cases.
// Known bugs: volume *may* still be off for a lot of samples. Importantly,
// waveform volume is too quiet but setting it at the correct volume makes
// the noise volume too loud and vice-versa. I *think* what I have currently
// is mostly correct (I'm basing this mostly on how good Strawberry Crisis
// sounds with the given settings), but it's possible that more fine-tuning
// is needed. Apart from that, this is probably the sketchiest part of all
// of my emulator code, but then again there's a bit-exact VHDL core of
// the YM2149F/AY-3-8910, so while I do want to make this as good
// as the code in opna.c, it's the lowest-priority of all of the code here.
// --bofh */
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "op.h"
#include "psg.h"

/* ---------------------------------------------------------------------------
// ????
*/
int      EmitTable[0x20] = { -1, };
uint32_t enveloptable[16][64] = { { 0, }, };

/* ---------------------------------------------------------------------------
//  PSG reset to power-on defaults
*/
void PSGReset(PSG *psg)
{
    int i;
    for (i=0; i<14; i++)
        PSGSetReg(psg, i, 0);
    PSGSetReg(psg, 7, 0xff);
    PSGSetReg(psg, 14, 0xff);
    PSGSetReg(psg, 15, 0xff);
}

/* ---------------------------------------------------------------------------
// This code is strongly inspired by some random PSG emulator code I found,
// and is probably not the optimal way to define periods. It *is* at least
// among the fastest, given that it uses the hilarious hack of using the
// integer overflow on a 32-bit unsigned integer to compute ""moduli"".
*/
void PSGSetClock(PSG *psg, uint32_t clock, uint32_t rate)
{
    int tmp;
    psg->tperiodbase = (uint32_t)((1 << toneshift ) / 4.0f * clock / rate);
    psg->eperiodbase = (uint32_t)((1 << envshift  ) / 4.0f * clock / rate);

    tmp = ((psg->reg[0] + psg->reg[1] * 256) & 0xfff);
    psg->speriod[0] = tmp ? psg->tperiodbase / tmp : psg->tperiodbase;
    tmp = ((psg->reg[2] + psg->reg[3] * 256) & 0xfff);
    psg->speriod[1] = tmp ? psg->tperiodbase / tmp : psg->tperiodbase;
    tmp = ((psg->reg[4] + psg->reg[5] * 256) & 0xfff);
    psg->speriod[2] = tmp ? psg->tperiodbase / tmp : psg->tperiodbase;
    tmp = psg->reg[6] & 0x1f;
    psg->nperiod = tmp;
    tmp = ((psg->reg[11] + psg->reg[12] * 256) & 0xffff);
    psg->eperiod = tmp ? psg->eperiodbase / tmp : psg->eperiodbase * 2;
}

/* ---------------------------------------------------------------------------
// ????????????
*/
static uint8_t table3[4] = {  0,  1, -1,  0 };
void MakeEnvelopTable(void)
{
    /* 0 lo  1 up 2 down 3 hi */
    static uint8_t table1[16*2] =
    {
        2,0, 2,0, 2,0, 2,0, 1,0, 1,0, 1,0, 1,0,
        2,2, 2,0, 2,1, 2,3, 1,1, 1,3, 1,2, 1,0,
    };
    int i, j;

    if (!enveloptable[0][0]) {
        uint32_t *ptr = enveloptable[0];
        for (i=0; i<16*2; i++) {
            uint8_t v = ((table1[i] & 0x2) ? 31 : 0);
            for (j=0; j<32; j++) {
                *ptr++ = EmitTable[v];
                v += table3[table1[i]];
            }
        }
    }
}

/* ---------------------------------------------------------------------------
//  Sets the channel output mask for the PSG device.
//  c is a bitvector where the 3 LSBs are set to 0 to disable a given
//  PSG channel and 1 to enable it.
//  TODO: Possibly allow enabling tone/noise output for each channel independently?
*/
void PSGSetChannelMask(PSG *psg, int c)
{
    int i;
    psg->mask = c;
    for (i=0; i<3; i++)
        psg->olevel[i] = psg->mask & (1 << i) ? EmitTable[(psg->reg[8+i] & 15) * 2 + 1] : 0;
}

/* ---------------------------------------------------------------------------
//  PSG register set routine. Mostly just what you'd expect from reading the manual.
//  Fairly boring code overall. regnum can be 0 - 15, data can be 0x00 - 0xFF.
//  (This should not be surprising - the YM2149F *did* use an 8-bit bus, after all).
//  Interesting quirk: the task of register 7 (channel enable/disable) is basically
//  entirely duplicated by other registers, to the point where you can basically
//  just ignore any writes to register 7 entirely. I save it here in case some
//  braindead routine wants to read its value and do something based on that
//  (Another curiosity: register 7 on the PSG appears to be the only register
//   between *both* the OPNA and the PSG which is actually *read from* by
//   pmdwin.cpp and not just written to. Amusingly enough, the only reason
//   that it is ever read is so that it can then OR something with what it just read
//   and then write that back to register 7. Hilarity).
//  HACK ALERT: The output levels for channels 0 and 1 are increased by a factor of 4
//  to make them match the actual chip in loudness, but without causing the noise channel
//  to overtake everything in intensity. This is almost certainly wrong, and moreover
//  it assumes that channel 2 will be playing back Speak Board effects which usually means
//  drum kit only (for the most part, at least), and not being used as a separate tonal
//  channel in its own right. To the best of my knowledge, this does hold for all of ZUN's
//  songs, however, once you step outside that set of music, it's trivial to find
//  all sorts of counterexamples to that assumption. Therefore, this should be fixed ASAP.
*/
void PSGSetReg(PSG *psg, uint8_t regnum, uint8_t data)
{
    if (regnum < 0x10)
    {
        psg->reg[regnum] = data;
        switch (regnum)
        {
            int tmp;

        case 0:     /* ChA Fine Tune */
        case 1:     /* ChA Coarse Tune */
            tmp = ((psg->reg[0] + psg->reg[1] * 256) & 0xfff);
            psg->speriod[0] = tmp ? psg->tperiodbase / tmp : psg->tperiodbase;
            break;

        case 2:     /* ChB Fine Tune */
        case 3:     /* ChB Coarse Tune */
            tmp = ((psg->reg[2] + psg->reg[3] * 256) & 0xfff);
            psg->speriod[1] = tmp ? psg->tperiodbase / tmp : psg->tperiodbase;
            break;

        case 4:     /* ChC Fine Tune */
        case 5:     /* ChC Coarse Tune */
            tmp = ((psg->reg[4] + psg->reg[5] * 256) & 0xfff);
            psg->speriod[2] = tmp ? psg->tperiodbase / tmp : psg->tperiodbase;
            break;

        case 6:     /* Noise generator control */
            data &= 0x1f;
            psg->nperiod = data;
            break;

        case 8:
            psg->olevel[0] = psg->mask & 1 ? EmitTable[(data & 15) * 2 + 1] : 0;
            break;

        case 9:
            psg->olevel[1] = psg->mask & 2 ? EmitTable[(data & 15) * 2 + 1] : 0;
            break;

        case 10:
            psg->olevel[2] = psg->mask & 4 ? EmitTable[(data & 15) * 2 + 1] : 0;
            break;

        case 11:    /* Envelope period */
        case 12:
            tmp = ((psg->reg[11] + psg->reg[12] * 256) & 0xffff);
            psg->eperiod = tmp ? psg->eperiodbase / tmp : psg->eperiodbase * 2;
            break;

        case 13:    /* Envelope shape */
            psg->ecount = 0;
            psg->envelop = enveloptable[data & 15];
            break;
        }
    }
}

/* ---------------------------------------------------------------------------
// Init code. Set volume to 0, reset the chip, enable all channels, seed the RNG.
// RNG seed lifted from MAME's YM2149F emulation routine, appears to be correct.
*/
void PSGInit(PSG *psg)
{
    int i;
    float base = 0x4000 / 3.0f;
    for (i=31; i>=2; i--)
    {
        EmitTable[i] = lrintf(base);
        base *= 0.840896415f; /* 1.0f / 1.189207115f */
    }
    EmitTable[1] = 0;
    EmitTable[0] = 0;
    MakeEnvelopTable();

    PSGSetChannelMask(psg, psg->mask);
    psg->rng = 14231;
    psg->ncount = 0;
    PSGReset(psg);
    psg->mask = 0x3f;
}

/* ---------------------------------------------------------------------------
// The main output routine for the PSG emulation.
// dest should be an array of size nsamples, and of type Sample
// (one of int16_t, int32_t or float - any will work here without causing
//  clipping/precision problems).
// Everything is implemented using some form of fixed-point arithmetic
// that currently needs no more than 32-bits for its implementation,
// but I'm pretty certain that you can get by with much less than that
// and still have mostly correct-to-fully-correct emulation.
//
// TODO: In the future, test the veracity of the above statement. Moreover,
// if it turns out to be correct, rewrite this routine to not use more than
// the required precision. This is irrelevant for any PC newer than, well,
// a 386DX/68040, but important for efficient hardware implementation.
*/
void PSGMix(PSG *psg, int32_t *dest, uint32_t nsamples)
{
    uint8_t chenable[3];
    uint8_t r7 = ~psg->reg[7];
    unsigned int i, k = 0;
    int x, y, z;

    if ((r7 & 0x3f) | ((psg->reg[8] | psg->reg[9] | psg->reg[10]) & 0x1f)) {
        int noise, sample;
        uint32_t env;
        uint32_t* p1;
        uint32_t* p2;
        uint32_t* p3;

        chenable[0] = (r7 & 0x01) && (psg->speriod[0] <= (1 << toneshift));
        chenable[1] = (r7 & 0x02) && (psg->speriod[1] <= (1 << toneshift));
        chenable[2] = (r7 & 0x04) && (psg->speriod[2] <= (1 << toneshift));

        p1 = ((psg->mask & 1) && (psg->reg[ 8] & 0x10)) ? &env : &psg->olevel[0];
        p2 = ((psg->mask & 2) && (psg->reg[ 9] & 0x10)) ? &env : &psg->olevel[1];
        p3 = ((psg->mask & 4) && (psg->reg[10] & 0x10)) ? &env : &psg->olevel[2];
        #define SCOUNT(ch)  (psg->scount[ch] >> toneshift)

        if (p1 != &env && p2 != &env && p3 != &env) {
            for (i=0; i<nsamples; i++) {
                psg->ncount++;
                if(psg->ncount >= psg->nperiod) {
                    if(psg->rng & 1)
                        psg->rng ^= 0x24000;
                    psg->rng >>= 1;
                    psg->ncount = 0;
                }
                noise = (psg->rng & 1);
                sample = 0;
                {
                    x = ((SCOUNT(0) & chenable[0]) | ((r7 >> 3) & noise)) - 1;     /* 0 or -1 */
                    sample += (psg->olevel[0] + x) ^ x;
                    psg->scount[0] += psg->speriod[0];
                    y = ((SCOUNT(1) & chenable[1]) | ((r7 >> 4) & noise)) - 1;
                    sample += (psg->olevel[1] + y) ^ y;
                    psg->scount[1] += psg->speriod[1];
                    /*z = ((SCOUNT(2) & chenable[2]) | ((r7 >> 5) & noise)) - 1;*/
                    z = ((r7 >> 5) & noise) - 1;
                    sample += (psg->olevel[2] + z) ^ z;
                    psg->scount[2] += psg->speriod[2];
                }
                sample = Limit16(sample);
                dest[k++] += sample;
                dest[k++] += sample;
            }

            psg->ecount = (psg->ecount >> 8) + (psg->eperiod >> 8) * nsamples;
            if (psg->ecount >= (1 << (envshift+6-8))) {
                if ((psg->reg[0x0d] & 0x0b) != 0x0a)
                    psg->ecount |= (1 << (envshift+5-8));
                psg->ecount &= (1 << (envshift+6-8)) - 1;
            }
            psg->ecount <<= 8;
        } else {
            for (i=0; i<nsamples; i++) {
                psg->ncount++;
                if(psg->ncount >= psg->nperiod) {
                    if(psg->rng & 1)
                        psg->rng ^= 0x24000;
                    psg->rng >>= 1;
                    psg->ncount = 0;
                }
                noise = (psg->rng & 1);
                sample = 0;
                {
                    env = psg->envelop[psg->ecount >> envshift];
                    psg->ecount += psg->eperiod;
                    if (psg->ecount >= (1 << (envshift+6))) {
                        if ((psg->reg[0x0d] & 0x0b) != 0x0a)
                            psg->ecount |= (1 << (envshift+5));
                        psg->ecount &= (1 << (envshift+6)) - 1;
                    }
                    x = ((SCOUNT(0) & chenable[0]) | ((r7 >> 3) & noise)) - 1;     /* 0 or -1 */
                    sample += (*p1 + x) ^ x;
                    psg->scount[0] += psg->speriod[0];
                    y = ((SCOUNT(1) & chenable[1]) | ((r7 >> 4) & noise)) - 1;
                    sample += (*p2 + y) ^ y;
                    psg->scount[1] += psg->speriod[1];
                    /*z = ((SCOUNT(2) & chenable[2]) | ((r7 >> 5) & noise)) - 1;*/
                    z = ((r7 >> 5) & noise) - 1;
                    sample += (*p3 + z) ^ z;
                    psg->scount[2] += psg->speriod[2];
                }
                sample = Limit16(sample);
                dest[k++] += sample;
                dest[k++] += sample;
            }
        }
    }
}