YM2413Burczynski.cc

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/*
 *
 * File: ym2413.c - software implementation of YM2413
 *                  FM sound generator type OPLL
 *
 * Copyright (C) 2002 Jarek Burczynski
 *
 * Version 1.0
 *
 *
 * TODO:
 *  - make sure of the sinus amplitude bits
 *  - make sure of the EG resolution bits (looks like the biggest
 *    modulation index generated by the modulator is 123, 124 = no modulation)
 *  - find proper algorithm for attack phase of EG
 *  - tune up instruments ROM
 *  - support sample replay in test mode (it is NOT as simple as setting bit 0
 *    in register 0x0f and using register 0x10 for sample data).
 *    Which games use this feature ?
 */
 
#include "YM2413Burczynski.hh"
#include "Math.hh"
#include "cstd.hh"
#include "ranges.hh"
#include "serialize.hh"
#include "xrange.hh"
#include <array>
#include <cstring>
#include <iostream>
 
namespace openmsx {
namespace YM2413Burczynski {
 
// envelope output entries
constexpr int ENV_BITS = 10;
constexpr double ENV_STEP = 128.0 / (1 << ENV_BITS);
 
constexpr int MAX_ATT_INDEX = (1 << (ENV_BITS - 2)) - 1; // 255
constexpr int MIN_ATT_INDEX = 0;
 
// sinwave entries
constexpr int SIN_BITS = 10;
constexpr int SIN_LEN  = 1 << SIN_BITS;
constexpr int SIN_MASK = SIN_LEN - 1;
 
constexpr int TL_RES_LEN = 256; // 8 bits addressing (real chip)
 
// key scale level
// table is 3dB/octave, DV converts this into 6dB/octave
// 0.1875 is bit 0 weight of the envelope counter (volume) expressed
// in the 'decibel' scale
static constexpr int DV(double x) { return int(x / 0.1875); }
constexpr int ksl_tab[8 * 16] =
{
        // OCT 0
        DV( 0.000),DV( 0.000),DV( 0.000),DV( 0.000),
        DV( 0.000),DV( 0.000),DV( 0.000),DV( 0.000),
        DV( 0.000),DV( 0.000),DV( 0.000),DV( 0.000),
        DV( 0.000),DV( 0.000),DV( 0.000),DV( 0.000),
        // OCT 1
        DV( 0.000),DV( 0.000),DV( 0.000),DV( 0.000),
        DV( 0.000),DV( 0.000),DV( 0.000),DV( 0.000),
        DV( 0.000),DV( 0.750),DV( 1.125),DV( 1.500),
        DV( 1.875),DV( 2.250),DV( 2.625),DV( 3.000),
        // OCT 2
        DV( 0.000),DV( 0.000),DV( 0.000),DV( 0.000),
        DV( 0.000),DV( 1.125),DV( 1.875),DV( 2.625),
        DV( 3.000),DV( 3.750),DV( 4.125),DV( 4.500),
        DV( 4.875),DV( 5.250),DV( 5.625),DV( 6.000),
        // OCT 3
        DV( 0.000),DV( 0.000),DV( 0.000),DV( 1.875),
        DV( 3.000),DV( 4.125),DV( 4.875),DV( 5.625),
        DV( 6.000),DV( 6.750),DV( 7.125),DV( 7.500),
        DV( 7.875),DV( 8.250),DV( 8.625),DV( 9.000),
        // OCT 4
        DV( 0.000),DV( 0.000),DV( 3.000),DV( 4.875),
        DV( 6.000),DV( 7.125),DV( 7.875),DV( 8.625),
        DV( 9.000),DV( 9.750),DV(10.125),DV(10.500),
        DV(10.875),DV(11.250),DV(11.625),DV(12.000),
        // OCT 5
        DV( 0.000),DV( 3.000),DV( 6.000),DV( 7.875),
        DV( 9.000),DV(10.125),DV(10.875),DV(11.625),
        DV(12.000),DV(12.750),DV(13.125),DV(13.500),
        DV(13.875),DV(14.250),DV(14.625),DV(15.000),
        // OCT 6
        DV( 0.000),DV( 6.000),DV( 9.000),DV(10.875),
        DV(12.000),DV(13.125),DV(13.875),DV(14.625),
        DV(15.000),DV(15.750),DV(16.125),DV(16.500),
        DV(16.875),DV(17.250),DV(17.625),DV(18.000),
        // OCT 7
        DV( 0.000),DV( 9.000),DV(12.000),DV(13.875),
        DV(15.000),DV(16.125),DV(16.875),DV(17.625),
        DV(18.000),DV(18.750),DV(19.125),DV(19.500),
        DV(19.875),DV(20.250),DV(20.625),DV(21.000)
};
 
// sustain level table (3dB per step)
// 0 - 15: 0, 3, 6, 9,12,15,18,21,24,27,30,33,36,39,42,45 (dB)
static constexpr int SC(int db) { return int(double(db) / ENV_STEP); }
constexpr int sl_tab[16] = {
        SC( 0),SC( 1),SC( 2),SC(3 ),SC(4 ),SC(5 ),SC(6 ),SC( 7),
        SC( 8),SC( 9),SC(10),SC(11),SC(12),SC(13),SC(14),SC(15)
};
 
constexpr uint8_t eg_inc[15][8] =
{
        // cycle: 0 1  2 3  4 5  6 7
 
        /* 0 */ { 0,1, 0,1, 0,1, 0,1, }, // rates 00..12 0 (increment by 0 or 1)
        /* 1 */ { 0,1, 0,1, 1,1, 0,1, }, // rates 00..12 1
        /* 2 */ { 0,1, 1,1, 0,1, 1,1, }, // rates 00..12 2
        /* 3 */ { 0,1, 1,1, 1,1, 1,1, }, // rates 00..12 3
 
        /* 4 */ { 1,1, 1,1, 1,1, 1,1, }, // rate 13 0 (increment by 1)
        /* 5 */ { 1,1, 1,2, 1,1, 1,2, }, // rate 13 1
        /* 6 */ { 1,2, 1,2, 1,2, 1,2, }, // rate 13 2
        /* 7 */ { 1,2, 2,2, 1,2, 2,2, }, // rate 13 3
 
        /* 8 */ { 2,2, 2,2, 2,2, 2,2, }, // rate 14 0 (increment by 2)
        /* 9 */ { 2,2, 2,4, 2,2, 2,4, }, // rate 14 1
        /*10 */ { 2,4, 2,4, 2,4, 2,4, }, // rate 14 2
        /*11 */ { 2,4, 4,4, 2,4, 4,4, }, // rate 14 3
 
        /*12 */ { 4,4, 4,4, 4,4, 4,4, }, // rates 15 0, 15 1, 15 2, 15 3 (incr by 4)
        /*13 */ { 8,8, 8,8, 8,8, 8,8, }, // rates 15 2, 15 3 for attack
        /*14 */ { 0,0, 0,0, 0,0, 0,0, }, // infinity rates for attack and decay(s)
};
 
// note that there is no value 13 in this table - it's directly in the code
constexpr uint8_t eg_rate_select[16 + 64 + 16] =
{
        // Envelope Generator rates (16 + 64 rates + 16 RKS)
        // 16 infinite time rates
        14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
 
        // rates 00-12
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
         0, 1, 2, 3,
 
        // rate 13
         4, 5, 6, 7,
 
        // rate 14
         8, 9,10,11,
 
        // rate 15
        12,12,12,12,
 
        // 16 dummy rates (same as 15 3)
        12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,
};
 
// rate  0,    1,    2,    3,    4,   5,   6,   7,  8,  9, 10, 11, 12, 13, 14, 15
// shift 13,   12,   11,   10,   9,   8,   7,   6,  5,  4,  3,  2,  1,  0,  0,  0
// mask  8191, 4095, 2047, 1023, 511, 255, 127, 63, 31, 15, 7,  3,  1,  0,  0,  0
 
constexpr uint8_t eg_rate_shift[16 + 64 + 16] =
{
        // Envelope Generator counter shifts (16 + 64 rates + 16 RKS)
        // 16 infinite time rates
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 
        // rates 00-12
        13,13,13,13,
        12,12,12,12,
        11,11,11,11,
        10,10,10,10,
         9, 9, 9, 9,
         8, 8, 8, 8,
         7, 7, 7, 7,
         6, 6, 6, 6,
         5, 5, 5, 5,
         4, 4, 4, 4,
         3, 3, 3, 3,
         2, 2, 2, 2,
         1, 1, 1, 1,
 
        // rate 13
         0, 0, 0, 0,
 
        // rate 14
         0, 0, 0, 0,
 
        // rate 15
         0, 0, 0, 0,
 
        // 16 dummy rates (same as 15 3)
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
};
 
// multiple table
static constexpr uint8_t ML(double x) { return uint8_t(2 * x); }
constexpr uint8_t mul_tab[16] =
{
        ML( 0.50), ML( 1.00), ML( 2.00), ML( 3.00),
        ML( 4.00), ML( 5.00), ML( 6.00), ML( 7.00),
        ML( 8.00), ML( 9.00), ML(10.00), ML(10.00),
        ML(12.00), ML(12.00), ML(15.00), ML(15.00),
};
 
//  TL_TAB_LEN is calculated as:
//  11 - sinus amplitude bits     (Y axis)
//  2  - sinus sign bit           (Y axis)
//  TL_RES_LEN - sinus resolution (X axis)
constexpr int TL_TAB_LEN = 11 * 2 * TL_RES_LEN;
constexpr auto tlTab = [] {
        std::array<int, TL_TAB_LEN> result = {};
        for (auto x : xrange(TL_RES_LEN)) {
                double m = (1 << 16) / cstd::exp2<6>((x + 1) * (ENV_STEP / 4.0) / 8.0);
 
                // we never reach (1 << 16) here due to the (x + 1)
                // result fits within 16 bits at maximum
                int n = int(m); // 16 bits here
                n >>= 4;        // 12 bits here
                n = (n >> 1) + (n & 1); // round to nearest
                // 11 bits here (rounded)
                for (auto i : xrange(11)) {
                        result[x * 2 + 0 + i * 2 * TL_RES_LEN] = n >> i;
                        result[x * 2 + 1 + i * 2 * TL_RES_LEN] = -(n >> i);
                }
        }
        return result;
}();
 
// sin waveform table in 'decibel' scale
// two waveforms on OPLL type chips
constexpr auto sinTab = [] {
        std::array<unsigned, SIN_LEN * 2> result = {};
        for (auto i : xrange(SIN_LEN / 4)) {
                // checked on real hardware, see also
                //   http://docs.google.com/Doc?id=dd8kqn9f_13cqjkf4gp
                double m = cstd::sin<2>(((i * 2) + 1) * M_PI / SIN_LEN);
                int n = int(cstd::round(cstd::log2<8, 3>(m) * -256.0));
                result[i] = 2 * n;
        }
        for (auto i : xrange(SIN_LEN / 4)) {
                result[SIN_LEN / 4 + i] = result[SIN_LEN / 4 - 1 - i];
        }
        for (auto i : xrange(SIN_LEN / 2)) {
                result[SIN_LEN / 2 + i] = result[i] | 1;
        }
        for (auto i : xrange(SIN_LEN / 2)) {
                result[i + SIN_LEN] = result[i];
        }
        for (auto i : xrange(SIN_LEN / 2)) {
                result[i + SIN_LEN + SIN_LEN / 2] = TL_TAB_LEN;
        }
        return result;
}();
 
// LFO Amplitude Modulation table (verified on real YM3812)
// 27 output levels (triangle waveform);
// 1 level takes one of: 192, 256 or 448 samples
//
// Length: 210 elements.
//
//  Each of the elements has to be repeated
//  exactly 64 times (on 64 consecutive samples).
//  The whole table takes: 64 * 210 = 13440 samples.
//
// We use data>>1, until we find what it really is on real chip...
 
constexpr int LFO_AM_TAB_ELEMENTS = 210;
constexpr uint8_t lfo_am_table[LFO_AM_TAB_ELEMENTS] =
{
        0,0,0,0,0,0,0,
        1,1,1,1,
        2,2,2,2,
        3,3,3,3,
        4,4,4,4,
        5,5,5,5,
        6,6,6,6,
        7,7,7,7,
        8,8,8,8,
        9,9,9,9,
        10,10,10,10,
        11,11,11,11,
        12,12,12,12,
        13,13,13,13,
        14,14,14,14,
        15,15,15,15,
        16,16,16,16,
        17,17,17,17,
        18,18,18,18,
        19,19,19,19,
        20,20,20,20,
        21,21,21,21,
        22,22,22,22,
        23,23,23,23,
        24,24,24,24,
        25,25,25,25,
        26,26,26,
        25,25,25,25,
        24,24,24,24,
        23,23,23,23,
        22,22,22,22,
        21,21,21,21,
        20,20,20,20,
        19,19,19,19,
        18,18,18,18,
        17,17,17,17,
        16,16,16,16,
        15,15,15,15,
        14,14,14,14,
        13,13,13,13,
        12,12,12,12,
        11,11,11,11,
        10,10,10,10,
        9,9,9,9,
        8,8,8,8,
        7,7,7,7,
        6,6,6,6,
        5,5,5,5,
        4,4,4,4,
        3,3,3,3,
        2,2,2,2,
        1,1,1,1
};
 
// LFO Phase Modulation table (verified on real YM2413)
constexpr signed char lfo_pm_table[8][8] =
{
        // FNUM2/FNUM = 0 00xxxxxx (0x0000)
        { 0, 0, 0, 0, 0, 0, 0, 0, },
 
        // FNUM2/FNUM = 0 01xxxxxx (0x0040)
        { 1, 0, 0, 0,-1, 0, 0, 0, },
 
        // FNUM2/FNUM = 0 10xxxxxx (0x0080)
        { 2, 1, 0,-1,-2,-1, 0, 1, },
 
        // FNUM2/FNUM = 0 11xxxxxx (0x00C0)
        { 3, 1, 0,-1,-3,-1, 0, 1, },
 
        // FNUM2/FNUM = 1 00xxxxxx (0x0100)
        { 4, 2, 0,-2,-4,-2, 0, 2, },
 
        // FNUM2/FNUM = 1 01xxxxxx (0x0140)
        { 5, 2, 0,-2,-5,-2, 0, 2, },
 
        // FNUM2/FNUM = 1 10xxxxxx (0x0180)
        { 6, 3, 0,-3,-6,-3, 0, 3, },
 
        // FNUM2/FNUM = 1 11xxxxxx (0x01C0)
        { 7, 3, 0,-3,-7,-3, 0, 3, },
};
 
// This is not 100% perfect yet but very close
//
// - multi parameters are 100% correct (instruments and drums)
// - LFO PM and AM enable are 100% correct
// - waveform DC and DM select are 100% correct
constexpr uint8_t table[16 + 3][8] = {
        // MULT  MULT modTL DcDmFb AR/DR AR/DR SL/RR SL/RR
        //   0     1     2     3     4     5     6     7
        { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }, // user instrument
        { 0x61, 0x61, 0x1e, 0x17, 0xf0, 0x7f, 0x00, 0x17 }, // violin
        { 0x13, 0x41, 0x16, 0x0e, 0xfd, 0xf4, 0x23, 0x23 }, // guitar
        { 0x03, 0x01, 0x9a, 0x04, 0xf3, 0xf3, 0x13, 0xf3 }, // piano
        { 0x11, 0x61, 0x0e, 0x07, 0xfa, 0x64, 0x70, 0x17 }, // flute
        { 0x22, 0x21, 0x1e, 0x06, 0xf0, 0x76, 0x00, 0x28 }, // clarinet
        { 0x21, 0x22, 0x16, 0x05, 0xf0, 0x71, 0x00, 0x18 }, // oboe
        { 0x21, 0x61, 0x1d, 0x07, 0x82, 0x80, 0x17, 0x17 }, // trumpet
        { 0x23, 0x21, 0x2d, 0x16, 0x90, 0x90, 0x00, 0x07 }, // organ
        { 0x21, 0x21, 0x1b, 0x06, 0x64, 0x65, 0x10, 0x17 }, // horn
        { 0x21, 0x21, 0x0b, 0x1a, 0x85, 0xa0, 0x70, 0x07 }, // synthesizer
        { 0x23, 0x01, 0x83, 0x10, 0xff, 0xb4, 0x10, 0xf4 }, // harpsichord
        { 0x97, 0xc1, 0x20, 0x07, 0xff, 0xf4, 0x22, 0x22 }, // vibraphone
        { 0x61, 0x00, 0x0c, 0x05, 0xc2, 0xf6, 0x40, 0x44 }, // synthesizer bass
        { 0x01, 0x01, 0x56, 0x03, 0x94, 0xc2, 0x03, 0x12 }, // acoustic bass
        { 0x21, 0x01, 0x89, 0x03, 0xf1, 0xe4, 0xf0, 0x23 }, // electric guitar
        // drum instruments definitions
        // MULTI MULTI modTL  xxx  AR/DR AR/DR SL/RR SL/RR
        //   0     1     2     3     4     5     6     7
        //{ 0x07, 0x21, 0x14, 0x00, 0xee, 0xf8, 0xff, 0xf8 },
        //{ 0x01, 0x31, 0x00, 0x00, 0xf8, 0xf7, 0xf8, 0xf7 },
        //{ 0x25, 0x11, 0x00, 0x00, 0xf8, 0xfa, 0xf8, 0x55 }
        { 0x01, 0x01, 0x16, 0x00, 0xfd, 0xf8, 0x2f, 0x6d },// BD(multi verified, modTL verified, mod env - verified(close), carr. env verified)
        { 0x01, 0x01, 0x00, 0x00, 0xd8, 0xd8, 0xf9, 0xf8 },// HH(multi verified), SD(multi not used)
        { 0x05, 0x01, 0x00, 0x00, 0xf8, 0xba, 0x49, 0x55 },// TOM(multi,env verified), TOP CYM(multi verified, env verified)
};
 
static constexpr FreqIndex fnumToIncrement(int block_fnum)
{
        // OPLL (YM2413) phase increment counter = 18bit
        // Chip works with 10.10 fixed point, while we use 16.16.
        const int block = (block_fnum & 0x1C00) >> 10;
        return FreqIndex(block_fnum & 0x03FF) >> (11 - block);
}
 
inline int Slot::calc_envelope(Channel& channel, unsigned eg_cnt, bool carrier)
{
        switch (state) {
        case EG_DUMP:
                // Dump phase is performed by both operators in each channel.
                // When CARRIER envelope gets down to zero level, phases in BOTH
                // operators are reset (at the same time?).
                // TODO: That sounds logical, but it does not match the implementation.
                if (!(eg_cnt & eg_mask_dp)) {
                        egOut += eg_sel_dp[(eg_cnt >> eg_sh_dp) & 7];
                        if (egOut >= MAX_ATT_INDEX) {
                                egOut = MAX_ATT_INDEX;
                                setEnvelopeState(EG_ATTACK);
                                phase = FreqIndex(0); // restart Phase Generator
                        }
                }
                break;
 
        case EG_ATTACK:
                if (!(eg_cnt & eg_mask_ar)) {
                        egOut +=
                                (~egOut * eg_sel_ar[(eg_cnt >> eg_sh_ar) & 7]) >> 2;
                        if (egOut <= MIN_ATT_INDEX) {
                                egOut = MIN_ATT_INDEX;
                                setEnvelopeState(EG_DECAY);
                        }
                }
                break;
 
        case EG_DECAY:
                if (!(eg_cnt & eg_mask_dr)) {
                        egOut += eg_sel_dr[(eg_cnt >> eg_sh_dr) & 7];
                        if (egOut >= sl) {
                                setEnvelopeState(EG_SUSTAIN);
                        }
                }
                break;
 
        case EG_SUSTAIN:
                // this is important behaviour:
                // one can change percussive/non-percussive modes on the fly and
                // the chip will remain in sustain phase
                // - verified on real YM3812
                if (eg_sustain) {
                        // non-percussive mode (sustained tone)
                        // do nothing
                } else {
                        // percussive mode
                        // during sustain phase chip adds Release Rate (in
                        // percussive mode)
                        if (!(eg_cnt & eg_mask_rr)) {
                                egOut += eg_sel_rr[(eg_cnt >> eg_sh_rr) & 7];
                                if (egOut >= MAX_ATT_INDEX) {
                                        egOut = MAX_ATT_INDEX;
                                }
                        }
                        // else do nothing in sustain phase
                }
                break;
 
        case EG_RELEASE:
                // Exclude modulators in melody channels from performing anything in
                // this mode.
                if (carrier) {
                        const bool sustain = !eg_sustain || channel.isSustained();
                        const unsigned mask = sustain ? eg_mask_rs : eg_mask_rr;
                        if (!(eg_cnt & mask)) {
                                const uint8_t shift = sustain ? eg_sh_rs : eg_sh_rr;
                                const uint8_t* sel = sustain ? eg_sel_rs : eg_sel_rr;
                                egOut += sel[(eg_cnt >> shift) & 7];
                                if (egOut >= MAX_ATT_INDEX) {
                                        egOut = MAX_ATT_INDEX;
                                        setEnvelopeState(EG_OFF);
                                }
                        }
                }
                break;
 
        case EG_OFF:
                break;
        }
        return egOut;
}
 
inline int Slot::calc_phase(Channel& channel, unsigned lfo_pm)
{
        if (vib) {
                const int lfo_fn_table_index_offset = lfo_pm_table
                        [(channel.getBlockFNum() & 0x01FF) >> 6][lfo_pm];
                phase += fnumToIncrement(
                        channel.getBlockFNum() * 2 + lfo_fn_table_index_offset
                        ) * mul;
        } else {
                // LFO phase modulation disabled for this operator
                phase += freq;
        }
        return phase.toInt();
}
 
inline void Slot::updateTotalLevel(Channel& channel)
{
        TLL = TL + (channel.getKeyScaleLevelBase() >> ksl);
}
 
inline void Slot::updateAttackRate(int kcodeScaled)
{
        if ((ar + kcodeScaled) < (16 + 62)) {
                eg_sh_ar  = eg_rate_shift[ar + kcodeScaled];
                eg_sel_ar = eg_inc[eg_rate_select[ar + kcodeScaled]];
        } else {
                eg_sh_ar  = 0;
                eg_sel_ar = eg_inc[13];
        }
        eg_mask_ar = (1 << eg_sh_ar) - 1;
}
 
inline void Slot::updateDecayRate(int kcodeScaled)
{
        eg_sh_dr  = eg_rate_shift[dr + kcodeScaled];
        eg_sel_dr = eg_inc[eg_rate_select[dr + kcodeScaled]];
        eg_mask_dr = (1 << eg_sh_dr) - 1;
}
 
inline void Slot::updateReleaseRate(int kcodeScaled)
{
        eg_sh_rr  = eg_rate_shift[rr + kcodeScaled];
        eg_sel_rr = eg_inc[eg_rate_select[rr + kcodeScaled]];
        eg_mask_rr = (1 << eg_sh_rr) - 1;
}
 
inline int Slot::calcOutput(Channel& channel, unsigned eg_cnt, bool carrier,
                            unsigned lfo_am, int phase2)
{
        int egOut2 = calc_envelope(channel, eg_cnt, carrier);
        int env = (TLL + egOut2 + (lfo_am & AMmask)) << 5;
        int p = env + wavetable[phase2 & SIN_MASK];
        return p < TL_TAB_LEN ? tlTab[p] : 0;
}
 
inline int Slot::calc_slot_mod(Channel& channel, unsigned eg_cnt, bool carrier,
                               unsigned lfo_pm, unsigned lfo_am)
{
        // Compute phase.
        int phase2 = calc_phase(channel, lfo_pm);
        if (fb_shift) {
                phase2 += (op1_out[0] + op1_out[1]) >> fb_shift;
        }
        // Shift output in 2-place buffer.
        op1_out[0] = op1_out[1];
        // Calculate operator output.
        op1_out[1] = calcOutput(channel, eg_cnt, carrier, lfo_am, phase2);
        return op1_out[0] << 1;
}
 
inline int Channel::calcOutput(unsigned eg_cnt, unsigned lfo_pm, unsigned lfo_am, int fm)
{
        int phase = car.calc_phase(*this, lfo_pm) + fm;
        return car.calcOutput(*this, eg_cnt, true, lfo_am, phase);
}
 
 
// Operators used in the rhythm sounds generation process:
//
// Envelope Generator:
//
// channel  operator  register number   Bass  High  Snare Tom  Top
// / slot   number    TL ARDR SLRR Wave Drum  Hat   Drum  Tom  Cymbal
//  6 / 0   12        50  70   90   f0  +
//  6 / 1   15        53  73   93   f3  +
//  7 / 0   13        51  71   91   f1        +
//  7 / 1   16        54  74   94   f4              +
//  8 / 0   14        52  72   92   f2                    +
//  8 / 1   17        55  75   95   f5                          +
//
// Phase Generator:
//
// channel  operator  register number   Bass  High  Snare Tom  Top
// / slot   number    MULTIPLE          Drum  Hat   Drum  Tom  Cymbal
//  6 / 0   12        30                +
//  6 / 1   15        33                +
//  7 / 0   13        31                      +     +           +
//  7 / 1   16        34                -----  n o t  u s e d -----
//  8 / 0   14        32                                  +
//  8 / 1   17        35                      +                 +
//
// channel  operator  register number   Bass  High  Snare Tom  Top
// number   number    BLK/FNUM2 FNUM    Drum  Hat   Drum  Tom  Cymbal
//    6     12,15     B6        A6      +
//    7     13,16     B7        A7            +     +           +
//    8     14,17     B8        A8            +           +     +
 
// Phase generation is based on:
//   HH  (13) channel 7->slot 1 combined with channel 8->slot 2
//            (same combination as TOP CYMBAL but different output phases)
//   SD  (16) channel 7->slot 1
//   TOM (14) channel 8->slot 1
//   TOP (17) channel 7->slot 1 combined with channel 8->slot 2
//            (same combination as HIGH HAT but different output phases)
 
static constexpr int genPhaseHighHat(int phaseM7, int phaseC8, int noise_rng)
{
        // hi == phase >= 0x200
        // enable gate based on frequency of operator 2 in channel 8
        bool hi = [&] {
                if (phaseC8 & 0x28) {
                        return true;
                } else {
                        // base frequency derived from operator 1 in channel 7
                        // VC++ requires explicit conversion to bool. Compiler bug??
                        const bool bit7 = (phaseM7 & 0x80) != 0;
                        const bool bit3 = (phaseM7 & 0x08) != 0;
                        const bool bit2 = (phaseM7 & 0x04) != 0;
                        return bool((bit2 ^ bit7) | bit3);
                }
        }();
        if (noise_rng & 1) {
                return hi ? (0x200 | 0xD0) : (0xD0 >> 2);
        } else {
                return hi ? (0x200 | (0xD0 >> 2)) : 0xD0;
        }
}
 
static constexpr int genPhaseSnare(int phaseM7, int noise_rng)
{
        // base frequency derived from operator 1 in channel 7
        // noise bit XOR'es phase by 0x100
        return ((phaseM7 & 0x100) + 0x100)
             ^ ((noise_rng & 1) << 8);
}
 
static constexpr int genPhaseCymbal(int phaseM7, int phaseC8)
{
        // enable gate based on frequency of operator 2 in channel 8
        if (phaseC8 & 0x28) {
                return 0x300;
        } else {
                // base frequency derived from operator 1 in channel 7
                // VC++ requires explicit conversion to bool. Compiler bug??
                const bool bit7 = (phaseM7 & 0x80) != 0;
                const bool bit3 = (phaseM7 & 0x08) != 0;
                const bool bit2 = (phaseM7 & 0x04) != 0;
                return ((bit2 != bit7) || bit3) ? 0x300 : 0x100;
        }
}
 
 
Slot::Slot()
        : phase(0), freq(0)
{
        ar = dr = rr = KSR = ksl = mul = 0;
        fb_shift = op1_out[0] = op1_out[1] = 0;
        TL = TLL = egOut = sl = 0;
        eg_sh_dp   = eg_sh_ar   = eg_sh_dr   = eg_sh_rr   = eg_sh_rs   = 0;
        eg_sel_dp  = eg_sel_ar  = eg_sel_dr  = eg_sel_rr  = eg_sel_rs  = eg_inc[0];
        eg_mask_dp = eg_mask_ar = eg_mask_dr = eg_mask_rr = eg_mask_rs = 0;
        eg_sustain = false;
        setEnvelopeState(EG_OFF);
        key = AMmask = vib = 0;
        wavetable = &sinTab[0 * SIN_LEN];
}
 
void Slot::setKeyOn(KeyPart part)
{
        if (!key) {
                // do NOT restart Phase Generator (verified on real YM2413)
                setEnvelopeState(EG_DUMP);
        }
        key |= part;
}
 
void Slot::setKeyOff(KeyPart part)
{
        if (key) {
                key &= ~part;
                if (!key) {
                        if (isActive()) {
                                setEnvelopeState(EG_RELEASE);
                        }
                }
        }
}
 
void Slot::setKeyOnOff(KeyPart part, bool enabled)
{
        if (enabled) {
                setKeyOn(part);
        } else {
                setKeyOff(part);
        }
}
 
bool Slot::isActive() const
{
        return state != EG_OFF;
}
 
void Slot::setEnvelopeState(EnvelopeState state_)
{
        state = state_;
}
 
void Slot::setFrequencyMultiplier(uint8_t value)
{
        mul = mul_tab[value];
}
 
void Slot::setKeyScaleRate(bool value)
{
        KSR = value ? 0 : 2;
}
 
void Slot::setEnvelopeSustained(bool value)
{
        eg_sustain = value;
}
 
void Slot::setVibrato(bool value)
{
        vib = value;
}
 
void Slot::setAmplitudeModulation(bool value)
{
        AMmask = value ? ~0 : 0;
}
 
void Slot::setTotalLevel(Channel& channel, uint8_t value)
{
        TL = value << (ENV_BITS - 2 - 7); // 7 bits TL (bit 6 = always 0)
        updateTotalLevel(channel);
}
 
void Slot::setKeyScaleLevel(Channel& channel, uint8_t value)
{
        ksl = value ? (3 - value) : 31;
        updateTotalLevel(channel);
}
 
void Slot::setWaveform(uint8_t value)
{
        wavetable = &sinTab[value * SIN_LEN];
}
 
void Slot::setFeedbackShift(uint8_t value)
{
        fb_shift = value ? 8 - value : 0;
}
 
void Slot::setAttackRate(const Channel& channel, uint8_t value)
{
        int kcodeScaled = channel.getKeyCode() >> KSR;
        ar = value ? 16 + (value << 2) : 0;
        updateAttackRate(kcodeScaled);
}
 
void Slot::setDecayRate(const Channel& channel, uint8_t value)
{
        int kcodeScaled = channel.getKeyCode() >> KSR;
        dr = value ? 16 + (value << 2) : 0;
        updateDecayRate(kcodeScaled);
}
 
void Slot::setReleaseRate(const Channel& channel, uint8_t value)
{
        int kcodeScaled = channel.getKeyCode() >> KSR;
        rr = value ? 16 + (value << 2) : 0;
        updateReleaseRate(kcodeScaled);
}
 
void Slot::setSustainLevel(uint8_t value)
{
        sl = sl_tab[value];
}
 
void Slot::updateFrequency(Channel& channel)
{
        updateTotalLevel(channel);
        updateGenerators(channel);
}
 
void Slot::resetOperators()
{
        wavetable = &sinTab[0 * SIN_LEN];
        setEnvelopeState(EG_OFF);
        egOut = MAX_ATT_INDEX;
}
 
void Slot::updateGenerators(Channel& channel)
{
        // (frequency) phase increment counter
        freq = channel.getFrequencyIncrement() * mul;
 
        // calculate envelope generator rates
        const int kcodeScaled = channel.getKeyCode() >> KSR;
        updateAttackRate(kcodeScaled);
        updateDecayRate(kcodeScaled);
        updateReleaseRate(kcodeScaled);
 
        const int rs = channel.isSustained() ? 16 + (5 << 2) : 16 + (7 << 2);
        eg_sh_rs  = eg_rate_shift[rs + kcodeScaled];
        eg_sel_rs = eg_inc[eg_rate_select[rs + kcodeScaled]];
 
        const int dp = 16 + (13 << 2);
        eg_sh_dp  = eg_rate_shift[dp + kcodeScaled];
        eg_sel_dp = eg_inc[eg_rate_select[dp + kcodeScaled]];
 
        eg_mask_rs = (1 << eg_sh_rs) - 1;
        eg_mask_dp = (1 << eg_sh_dp) - 1;
}
 
Channel::Channel()
        : fc(0)
{
        block_fnum = ksl_base = 0;
        sus = false;
}
 
void Channel::setFrequency(int block_fnum_)
{
        if (block_fnum == block_fnum_) return;
        block_fnum = block_fnum_;
 
        ksl_base = ksl_tab[block_fnum >> 5];
        fc       = fnumToIncrement(block_fnum * 2);
 
        // Refresh Total Level and frequency counter in both SLOTs of this channel.
        mod.updateFrequency(*this);
        car.updateFrequency(*this);
}
 
void Channel::setFrequencyLow(uint8_t value)
{
        setFrequency((block_fnum & 0x0F00) | value);
}
 
void Channel::setFrequencyHigh(uint8_t value)
{
        setFrequency((value << 8) | (block_fnum & 0x00FF));
}
 
int Channel::getBlockFNum() const
{
        return block_fnum;
}
 
FreqIndex Channel::getFrequencyIncrement() const
{
        return fc;
}
 
int Channel::getKeyScaleLevelBase() const
{
        return ksl_base;
}
 
uint8_t Channel::getKeyCode() const
{
        // BLK 2,1,0 bits -> bits 3,2,1 of kcode, FNUM MSB -> kcode LSB
        return (block_fnum & 0x0F00) >> 8;
}
 
bool Channel::isSustained() const
{
        return sus;
}
 
void Channel::setSustain(bool sustained)
{
        sus = sustained;
}
 
void Channel::updateInstrumentPart(int part, uint8_t value)
{
        switch (part) {
        case 0:
                mod.setFrequencyMultiplier(value & 0x0F);
                mod.setKeyScaleRate((value & 0x10) != 0);
                mod.setEnvelopeSustained((value & 0x20) != 0);
                mod.setVibrato((value & 0x40) != 0);
                mod.setAmplitudeModulation((value & 0x80) != 0);
                mod.updateGenerators(*this);
                break;
        case 1:
                car.setFrequencyMultiplier(value & 0x0F);
                car.setKeyScaleRate((value & 0x10) != 0);
                car.setEnvelopeSustained((value & 0x20) != 0);
                car.setVibrato((value & 0x40) != 0);
                car.setAmplitudeModulation((value & 0x80) != 0);
                car.updateGenerators(*this);
                break;
        case 2:
                mod.setKeyScaleLevel(*this, value >> 6);
                mod.setTotalLevel(*this, value & 0x3F);
                break;
        case 3:
                mod.setWaveform((value & 0x08) >> 3);
                mod.setFeedbackShift(value & 0x07);
                car.setKeyScaleLevel(*this, value >> 6);
                car.setWaveform((value & 0x10) >> 4);
                break;
        case 4:
                mod.setAttackRate(*this, value >> 4);
                mod.setDecayRate(*this, value & 0x0F);
                break;
        case 5:
                car.setAttackRate(*this, value >> 4);
                car.setDecayRate(*this, value & 0x0F);
                break;
        case 6:
                mod.setSustainLevel(value >> 4);
                mod.setReleaseRate(*this, value & 0x0F);
                break;
        case 7:
                car.setSustainLevel(value >> 4);
                car.setReleaseRate(*this, value & 0x0F);
                break;
        }
}
 
void Channel::updateInstrument(const uint8_t* inst)
{
        for (auto part : xrange(8)) {
                updateInstrumentPart(part, inst[part]);
        }
}
 
YM2413::YM2413()
        : lfo_am_cnt(0), lfo_pm_cnt(0)
{
        if (false) {
                for (const auto& e : tlTab) std::cout << e << '\n';
                std::cout << '\n';
                for (const auto& e : sinTab) std::cout << e << '\n';
        }
 
        memset(reg, 0, sizeof(reg)); // avoid UMR
        eg_cnt = 0;
        noise_rng = 0;
 
        reset();
}
 
void YM2413::updateCustomInstrument(int part, uint8_t value)
{
        // Update instrument definition.
        inst_tab[0][part] = value;
 
        // Update every channel that has instrument 0 selected.
        for (auto ch : xrange(isRhythm() ? 6 : 9)) {
                Channel& channel = channels[ch];
                if ((reg[0x30 + ch] & 0xF0) == 0) {
                        channel.updateInstrumentPart(part, value);
                }
        }
}
 
void YM2413::setRhythmFlags(uint8_t old)
{
        Channel& ch6 = channels[6];
        Channel& ch7 = channels[7];
        Channel& ch8 = channels[8];
 
        // flags = X | X | mode | BD | SD | TOM | TC | HH
        uint8_t flags = reg[0x0E];
        if ((flags ^ old) & 0x20) {
                if (flags & 0x20) { // OFF -> ON
                        // Bass drum.
                        ch6.updateInstrument(inst_tab[16]);
                        // High hat and snare drum.
                        ch7.updateInstrument(inst_tab[17]);
                        ch7.mod.setTotalLevel(ch7, (reg[0x37] >> 4) << 2); // High hat
                        // Tom-tom and top cymbal.
                        ch8.updateInstrument(inst_tab[18]);
                        ch8.mod.setTotalLevel(ch8, (reg[0x38] >> 4) << 2); // Tom-tom
                } else { // ON -> OFF
                        ch6.updateInstrument(inst_tab[reg[0x36] >> 4]);
                        ch7.updateInstrument(inst_tab[reg[0x37] >> 4]);
                        ch8.updateInstrument(inst_tab[reg[0x38] >> 4]);
                        // BD key off
                        ch6.mod.setKeyOff(Slot::KEY_RHYTHM);
                        ch6.car.setKeyOff(Slot::KEY_RHYTHM);
                        // HH key off
                        ch7.mod.setKeyOff(Slot::KEY_RHYTHM);
                        // SD key off
                        ch7.car.setKeyOff(Slot::KEY_RHYTHM);
                        // TOM key off
                        ch8.mod.setKeyOff(Slot::KEY_RHYTHM);
                        // TOP-CY off
                        ch8.car.setKeyOff(Slot::KEY_RHYTHM);
                }
        }
        if (flags & 0x20) {
                // BD key on/off
                ch6.mod.setKeyOnOff(Slot::KEY_RHYTHM, (flags & 0x10) != 0);
                ch6.car.setKeyOnOff(Slot::KEY_RHYTHM, (flags & 0x10) != 0);
                // HH key on/off
                ch7.mod.setKeyOnOff(Slot::KEY_RHYTHM, (flags & 0x01) != 0);
                // SD key on/off
                ch7.car.setKeyOnOff(Slot::KEY_RHYTHM, (flags & 0x08) != 0);
                // TOM key on/off
                ch8.mod.setKeyOnOff(Slot::KEY_RHYTHM, (flags & 0x04) != 0);
                // TOP-CY key on/off
                ch8.car.setKeyOnOff(Slot::KEY_RHYTHM, (flags & 0x02) != 0);
        }
}
 
void YM2413::reset()
{
        eg_cnt    = 0;
        noise_rng = 1;    // noise shift register
        idleSamples = 0;
 
        // setup instruments table
        for (auto instrument : xrange(19)) {
                ranges::copy(table[instrument], inst_tab[instrument]);
        }
 
        // reset with register write
        writeReg(0x0F, 0); // test reg
        for (int i = 0x3F; i >= 0x10; --i) {
                writeReg(i, 0);
        }
        registerLatch = 0;
 
        resetOperators();
}
 
void YM2413::resetOperators()
{
        for (auto& ch : channels) {
                ch.mod.resetOperators();
                ch.car.resetOperators();
        }
}
 
bool YM2413::isRhythm() const
{
        return (reg[0x0E] & 0x20) != 0;
}
 
Channel& YM2413::getChannelForReg(uint8_t r)
{
        uint8_t chan = (r & 0x0F) % 9; // verified on real YM2413
        return channels[chan];
}
 
float YM2413::getAmplificationFactor() const
{
        return 1.0f / 2048.0f;
}
 
void YM2413::generateChannels(float* bufs[9 + 5], unsigned num)
{
        // TODO make channelActiveBits a member and
        //      keep it up-to-date all the time
 
        // bits 0-8  -> ch[0-8].car
        // bits 9-17 -> ch[0-8].mod (only ch7 and ch8 used)
        unsigned channelActiveBits = 0;
 
        for (auto ch : xrange(isRhythm() ? 6 : 9)) {
                if (channels[ch].car.isActive()) {
                        channelActiveBits |= 1 << ch;
                } else {
                        bufs[ch] = nullptr;
                }
        }
        if (isRhythm()) {
                std::fill_n(bufs + 6, 3, nullptr);
                for (auto ch : xrange(6, 9)) {
                        if (channels[ch].car.isActive()) {
                                channelActiveBits |= 1 << ch;
                        } else {
                                bufs[ch + 3] = nullptr;
                        }
                }
                if (channels[7].mod.isActive()) {
                        channelActiveBits |= 1 << (7 + 9);
                } else {
                        bufs[12] = nullptr;
                }
                if (channels[8].mod.isActive()) {
                        channelActiveBits |= 1 << (8 + 9);
                } else {
                        bufs[13] = nullptr;
                }
        } else {
                std::fill_n(bufs + 9, 5, nullptr);
        }
 
        if (channelActiveBits) {
                idleSamples = 0;
        } else {
                if (idleSamples > (CLOCK_FREQ / (72 * 5))) {
                        // Optimization:
                        //   idle for over 1/5s = 200ms
                        //   we don't care that noise / AM / PM isn't exactly
                        //   in sync with the real HW when music resumes
                        // Alternative:
                        //   implement an efficient advance(n) method
                        return;
                }
                idleSamples += num;
        }
 
        for (auto i : xrange(num)) {
                // Amplitude modulation: 27 output levels (triangle waveform)
                // 1 level takes one of: 192, 256 or 448 samples
                // One entry from LFO_AM_TABLE lasts for 64 samples
                lfo_am_cnt.addQuantum();
                if (lfo_am_cnt == LFOAMIndex(LFO_AM_TAB_ELEMENTS)) {
                        // lfo_am_table is 210 elements long
                        lfo_am_cnt = LFOAMIndex(0);
                }
                unsigned lfo_am = lfo_am_table[lfo_am_cnt.toInt()] >> 1;
                unsigned lfo_pm = lfo_pm_cnt.toInt() & 7;
 
                for (auto ch : xrange(isRhythm() ? 6 : 9)) {
                        Channel& channel = channels[ch];
                        int fm = channel.mod.calc_slot_mod(channel, eg_cnt, false, lfo_pm, lfo_am);
                        if ((channelActiveBits >> ch) & 1) {
                                bufs[ch][i] += channel.calcOutput(eg_cnt, lfo_pm, lfo_am, fm);
                        }
                }
                if (isRhythm()) {
                        // Bass Drum (verified on real YM3812):
                        //  - depends on the channel 6 'connect' register:
                        //    when connect = 0 it works the same as in normal (non-rhythm) mode
                        //                     (op1->op2->out)
                        //    when connect = 1 _only_ operator 2 is present on output (op2->out),
                        //                     operator 1 is ignored
                        //  - output sample always is multiplied by 2
                        Channel& channel6 = channels[6];
                        int fm = channel6.mod.calc_slot_mod(channels[6], eg_cnt, true, lfo_pm, lfo_am);
                        if (channelActiveBits & (1 << 6)) {
                                bufs[ 9][i] += 2 * channel6.calcOutput(eg_cnt, lfo_pm, lfo_am, fm);
                        }
 
                        // TODO: Skip phase generation if output will 0 anyway.
                        //       Possible by passing phase generator as a template parameter to
                        //       calcOutput.
 
                        /*C7*/  (void)channels[7].car.calc_phase(channels[7], lfo_pm);
                        int phaseM7 = channels[7].mod.calc_phase(channels[7], lfo_pm);
                        int phaseC8 = channels[8].car.calc_phase(channels[8], lfo_pm);
                        int phaseM8 = channels[8].mod.calc_phase(channels[8], lfo_pm);
 
                        // Snare Drum (verified on real YM3812)
                        if (channelActiveBits & (1 << 7)) {
                                Slot& SLOT7_2 = channels[7].car;
                                bufs[10][i] += 2 * SLOT7_2.calcOutput(channels[7], eg_cnt, true, lfo_am, genPhaseSnare(phaseM7, noise_rng));
                        }
 
                        // Top Cymbal (verified on real YM2413)
                        if (channelActiveBits & (1 << 8)) {
                                Slot& SLOT8_2 = channels[8].car;
                                bufs[11][i] += 2 * SLOT8_2.calcOutput(channels[8], eg_cnt, true, lfo_am, genPhaseCymbal(phaseM7, phaseC8));
                        }
 
                        // High Hat (verified on real YM3812)
                        if (channelActiveBits & (1 << (7 + 9))) {
                                Slot& SLOT7_1 = channels[7].mod;
                                bufs[12][i] += 2 * SLOT7_1.calcOutput(channels[7], eg_cnt, true, lfo_am, genPhaseHighHat(phaseM7, phaseC8, noise_rng));
                        }
 
                        // Tom Tom (verified on real YM3812)
                        if (channelActiveBits & (1 << (8 + 9))) {
                                Slot& SLOT8_1 = channels[8].mod;
                                bufs[13][i] += 2 * SLOT8_1.calcOutput(channels[8], eg_cnt, true, lfo_am, phaseM8);
                        }
                }
 
                // Vibrato: 8 output levels (triangle waveform)
                // 1 level takes 1024 samples
                lfo_pm_cnt.addQuantum();
 
                ++eg_cnt;
 
                // The Noise Generator of the YM3812 is 23-bit shift register.
                // Period is equal to 2^23-2 samples.
                // Register works at sampling frequency of the chip, so output
                // can change on every sample.
                //
                // Output of the register and input to the bit 22 is:
                // bit0 XOR bit14 XOR bit15 XOR bit22
                //
                // Simply use bit 22 as the noise output.
 
                //  int j = ((noise_rng >>  0) ^ (noise_rng >> 14) ^
                //           (noise_rng >> 15) ^ (noise_rng >> 22)) & 1;
                //  noise_rng = (j << 22) | (noise_rng >> 1);
                //
                //    Instead of doing all the logic operations above, we
                //    use a trick here (and use bit 0 as the noise output).
                //    The difference is only that the noise bit changes one
                //    step ahead. This doesn't matter since we don't know
                //    what is real state of the noise_rng after the reset.
                if (noise_rng & 1) {
                        noise_rng ^= 0x800302;
                }
                noise_rng >>= 1;
        }
}
 
void YM2413::writePort(bool port, uint8_t value, int /*offset*/)
{
        if (port == 0) {
                registerLatch = value;
        } else {
                writeReg(registerLatch & 0x3f, value);
        }
}
 
void YM2413::pokeReg(uint8_t r, uint8_t v)
{
        writeReg(r, v);
}
 
void YM2413::writeReg(uint8_t r, uint8_t v)
{
        uint8_t old = reg[r];
        reg[r] = v;
 
        switch (r & 0xF0) {
        case 0x00: { // 00-0F: control
                switch (r & 0x0F) {
                case 0x00:  // AM/VIB/EGTYP/KSR/MULTI (modulator)
                case 0x01:  // AM/VIB/EGTYP/KSR/MULTI (carrier)
                case 0x02:  // Key Scale Level, Total Level (modulator)
                case 0x03:  // Key Scale Level, carrier waveform, modulator waveform,
                            // Feedback
                case 0x04:  // Attack, Decay (modulator)
                case 0x05:  // Attack, Decay (carrier)
                case 0x06:  // Sustain, Release (modulator)
                case 0x07:  // Sustain, Release (carrier)
                        updateCustomInstrument(r, v);
                        break;
                case 0x0E:
                        setRhythmFlags(old);
                        break;
                }
                break;
        }
        case 0x10: {
                // 10-18: FNUM 0-7
                Channel& ch = getChannelForReg(r);
                ch.setFrequencyLow(v);
                break;
        }
        case 0x20: {
                // 20-28: susOn, keyOn, block, FNUM 8
                Channel& ch = getChannelForReg(r);
                ch.mod.setKeyOnOff(Slot::KEY_MAIN, (v & 0x10) != 0);
                ch.car.setKeyOnOff(Slot::KEY_MAIN, (v & 0x10) != 0);
                ch.setSustain((v & 0x20) != 0);
                // Note: When changing the frequency, a new value for RS is
                //       computed using the sustain value, so make sure the new
                //       sustain value is committed first.
                ch.setFrequencyHigh(v & 0x0F);
                break;
        }
        case 0x30: { // inst 4 MSBs, VOL 4 LSBs
                Channel& ch = getChannelForReg(r);
                ch.car.setTotalLevel(ch, (v & 0x0F) << 2);
 
                // Check wether we are in rhythm mode and handle instrument/volume
                // register accordingly.
 
                uint8_t chan = (r & 0x0F) % 9; // verified on real YM2413
                if (isRhythm() && (chan >= 6)) {
                        if (chan > 6) {
                                // channel 7 or 8 in rythm mode
                                // modulator envelope is HH(chan=7) or TOM(chan=8).
                                ch.mod.setTotalLevel(ch, (v >> 4) << 2);
                        }
                } else {
                        if ((old & 0xF0) != (v & 0xF0)) {
                                ch.updateInstrument(inst_tab[v >> 4]);
                        }
                }
                break;
        }
        default:
                break;
        }
}
 
uint8_t YM2413::peekReg(uint8_t r) const
{
        return reg[r];
}
 
} // namespace YM2413Burczynski
 
static constexpr std::initializer_list<enum_string<YM2413Burczynski::Slot::EnvelopeState>> envelopeStateInfo = {
        { "DUMP",    YM2413Burczynski::Slot::EG_DUMP    },
        { "ATTACK",  YM2413Burczynski::Slot::EG_ATTACK  },
        { "DECAY",   YM2413Burczynski::Slot::EG_DECAY   },
        { "SUSTAIN", YM2413Burczynski::Slot::EG_SUSTAIN },
        { "RELEASE", YM2413Burczynski::Slot::EG_RELEASE },
        { "OFF",     YM2413Burczynski::Slot::EG_OFF     }
};
SERIALIZE_ENUM(YM2413Burczynski::Slot::EnvelopeState, envelopeStateInfo);
 
namespace YM2413Burczynski {
 
// version 1: initial version
// version 2: - removed kcodeScaled
//            - calculated more members from other state
//              (TLL, freq, eg_sel_*, eg_sh_*)
template<typename Archive>
void Slot::serialize(Archive& a, unsigned /*version*/)
{
        // TODO some of the serialized members here could be calculated from
        //      other members
        int waveform = (wavetable == &sinTab[0]) ? 0 : 1;
        a.serialize("waveform", waveform);
        if (a.isLoader()) {
                setWaveform(waveform);
        }
 
        a.serialize("phase",      phase,
                    "TL",         TL,
                    "volume",     egOut,
                    "sl",         sl,
                    "state",      state,
                    "op1_out",    op1_out,
                    "eg_sustain", eg_sustain,
                    "fb_shift",   fb_shift,
                    "key",        key,
                    "ar",         ar,
                    "dr",         dr,
                    "rr",         rr,
                    "KSR",        KSR,
                    "ksl",        ksl,
                    "mul",        mul,
                    "AMmask",     AMmask,
                    "vib",        vib);
 
        // These are calculated by updateTotalLevel()
        //   TLL
        // These are calculated by updateGenerators()
        //   freq, eg_sh_ar, eg_sel_ar, eg_sh_dr, eg_sel_dr, eg_sh_rr, eg_sel_rr
        //   eg_sh_rs, eg_sel_rs, eg_sh_dp, eg_sel_dp
}
 
// version 1: original version
// version 2: removed kcode
// version 3: removed instvol_r
template<typename Archive>
void Channel::serialize(Archive& a, unsigned /*version*/)
{
        // mod/car were originally an array, keep serializing as such for bwc
        Slot slots[2] = { mod, car };
        a.serialize("slots", slots);
        if (a.isLoader()) {
                mod = slots[0];
                car = slots[1];
        }
 
        a.serialize("block_fnum", block_fnum,
                    "fc",         fc,
                    "ksl_base",   ksl_base,
                    "sus",        sus);
 
        if (a.isLoader()) {
                mod.updateFrequency(*this);
                car.updateFrequency(*this);
        }
}
 
// version 1: initial version
// version 2: 'registers' are moved here (no longer serialized in base class)
// version 3: removed 'rhythm' variable
// version 4: added 'registerLatch'
template<typename Archive>
void YM2413::serialize(Archive& a, unsigned version)
{
        if (a.versionBelow(version, 2)) a.beginTag("YM2413Core");
        a.serialize("registers", reg);
        if (a.versionBelow(version, 2)) a.endTag("YM2413Core");
 
        // only serialize user instrument
        a.serialize_blob("user_instrument", inst_tab[0], 8);
        a.serialize("channels",   channels,
                    "eg_cnt",     eg_cnt,
                    "noise_rng",  noise_rng,
                    "lfo_am_cnt", lfo_am_cnt,
                    "lfo_pm_cnt", lfo_pm_cnt);
        if (a.versionAtLeast(version, 4)) {
                a.serialize("registerLatch", registerLatch);
        } else {
                // could be restored from MSXMusicBase, worth the effort?
        }
        // don't serialize idleSamples, it's only an optimization
}
 
} // namespace YM2413Burczynski
 
using YM2413Burczynski::YM2413;
INSTANTIATE_SERIALIZE_METHODS(YM2413);
REGISTER_POLYMORPHIC_INITIALIZER(YM2413Core, YM2413, "YM2413-Jarek-Burczynski");
 
} // namespace openmsx