/*****************************************************************************
*
*	Yamaha YM2151 driver (version 2.150 final beta)
*
******************************************************************************/

#include "YM2151.hh"

#include "DeviceConfig.hh"
#include "serialize.hh"

#include "Math.hh"
#include "cstd.hh"
#include "enumerate.hh"
#include "narrow.hh"
#include "one_of.hh"
#include "ranges.hh"
#include "xrange.hh"

#include <algorithm>
#include <array>
#include <cassert>
#include <cmath>
#include <cstring>
#include <iostream>

namespace openmsx {

// TODO void ym2151WritePortCallback(void* ref, unsigned port, uint8_t value);

static constexpr int FREQ_SH  = 16; // 16.16 fixed point (frequency calculations)

static constexpr int FREQ_MASK = (1 << FREQ_SH) - 1;

static constexpr int ENV_BITS = 10;
static constexpr int ENV_LEN  = 1 << ENV_BITS;
static constexpr double ENV_STEP = 128.0 / ENV_LEN;

static constexpr int MAX_ATT_INDEX = ENV_LEN - 1; // 1023
static constexpr int MIN_ATT_INDEX = 0;

static constexpr unsigned EG_ATT = 4;
static constexpr unsigned EG_DEC = 3;
static constexpr unsigned EG_SUS = 2;
static constexpr unsigned EG_REL = 1;
static constexpr unsigned EG_OFF = 0;

static constexpr int SIN_BITS = 10;
static constexpr int SIN_LEN  = 1 << SIN_BITS;
static constexpr int SIN_MASK = SIN_LEN - 1;

static constexpr int TL_RES_LEN = 256; // 8 bits addressing (real chip)

// TL_TAB_LEN is calculated as:
//  13 - sinus amplitude bits     (Y axis)
//  2  - sinus sign bit           (Y axis)
// TL_RES_LEN - sinus resolution (X axis)
static constexpr unsigned TL_TAB_LEN = 13 * 2 * TL_RES_LEN;
static constexpr auto tl_tab = [] {
	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

		auto n = int(m); // 16 bits here
		n >>= 4;        // 12 bits here
		if (n & 1) {    // round to closest
			n = (n >> 1) + 1;
		} else {
			n = n >> 1;
		}
		// 11 bits here (rounded)
		n <<= 2; // 13 bits here (as in real chip)
		result[x * 2 + 0] = n;
		result[x * 2 + 1] = -result[x * 2 + 0];

		for (auto i : xrange(1, 13)) {
			result[x * 2 + 0 + i * 2 * TL_RES_LEN] =  result[x * 2 + 0] >> i;
			result[x * 2 + 1 + i * 2 * TL_RES_LEN] = -result[x * 2 + 0 + i * 2 * TL_RES_LEN];
		}
	}
	return result;
}();

static constexpr unsigned ENV_QUIET = TL_TAB_LEN >> 3;

// sin waveform table in 'decibel' scale
static constexpr auto sin_tab = [] {
	std::array<unsigned, SIN_LEN> result = {};
	for (auto i : xrange(SIN_LEN)) {
		// non-standard sinus
		double m = cstd::sin<2>((i * 2 + 1) * Math::pi / SIN_LEN); // verified on the real chip

		// we never reach zero here due to (i * 2 + 1)
		double o = -8.0 * cstd::log2<8, 3>(cstd::abs(m)); // convert to decibels
		o = o / (ENV_STEP / 4);

		auto n = int(2.0 * o);
		if (n & 1) { // round to closest
			n = (n >> 1) + 1;
		} else {
			n = n >> 1;
		}
		result[i] = n * 2 + (m >= 0.0 ? 0 : 1);
	}
	return result;
}();


// translate from D1L to volume index (16 D1L levels)
static constexpr auto d1l_tab = [] {
	std::array<unsigned, 16> result = {};
	//for (auto [i, r] : enumerate(result)) { msvc bug
	for (int i = 0; i < 16; ++i) {
		// every 3 'dB' except for all bits = 1 = 45+48 'dB'
		result[i] = unsigned((i != 15 ? i : i + 16) * (4.0 / ENV_STEP));
	}
	return result;
}();


static constexpr unsigned RATE_STEPS = 8;
static constexpr std::array<uint8_t, 19 * RATE_STEPS> eg_inc = {

//cycle:0 1  2 3  4 5  6 7

/* 0 */ 0,1, 0,1, 0,1, 0,1, // rates 00..11 0 (increment by 0 or 1)
/* 1 */ 0,1, 0,1, 1,1, 0,1, // rates 00..11 1
/* 2 */ 0,1, 1,1, 0,1, 1,1, // rates 00..11 2
/* 3 */ 0,1, 1,1, 1,1, 1,1, // rates 00..11 3

/* 4 */ 1,1, 1,1, 1,1, 1,1, // rate 12 0 (increment by 1)
/* 5 */ 1,1, 1,2, 1,1, 1,2, // rate 12 1
/* 6 */ 1,2, 1,2, 1,2, 1,2, // rate 12 2
/* 7 */ 1,2, 2,2, 1,2, 2,2, // rate 12 3

/* 8 */ 2,2, 2,2, 2,2, 2,2, // rate 13 0 (increment by 2)
/* 9 */ 2,2, 2,4, 2,2, 2,4, // rate 13 1
/*10 */ 2,4, 2,4, 2,4, 2,4, // rate 13 2
/*11 */ 2,4, 4,4, 2,4, 4,4, // rate 13 3

/*12 */ 4,4, 4,4, 4,4, 4,4, // rate 14 0 (increment by 4)
/*13 */ 4,4, 4,8, 4,4, 4,8, // rate 14 1
/*14 */ 4,8, 4,8, 4,8, 4,8, // rate 14 2
/*15 */ 4,8, 8,8, 4,8, 8,8, // rate 14 3

/*16 */ 8,8, 8,8, 8,8, 8,8, // rates 15 0, 15 1, 15 2, 15 3 (increment by 8)
/*17 */ 16,16,16,16,16,16,16,16, // rates 15 2, 15 3 for attack
/*18 */ 0,0, 0,0, 0,0, 0,0, // infinity rates for attack and decay(s)
};


static constexpr uint8_t O(int a) { return narrow<uint8_t>(a * RATE_STEPS); }
// note that there is no O(17) in this table - it's directly in the code
static constexpr std::array<uint8_t, 32 + 64 + 32> eg_rate_select {
// Envelope Generator rates (32 + 64 rates + 32 RKS)
// 32 dummy (infinite time) rates
O(18),O(18),O(18),O(18),O(18),O(18),O(18),O(18),
O(18),O(18),O(18),O(18),O(18),O(18),O(18),O(18),
O(18),O(18),O(18),O(18),O(18),O(18),O(18),O(18),
O(18),O(18),O(18),O(18),O(18),O(18),O(18),O(18),

// rates 00-11
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),
O( 0),O( 1),O( 2),O( 3),

// rate 12
O( 4),O( 5),O( 6),O( 7),

// rate 13
O( 8),O( 9),O(10),O(11),

// rate 14
O(12),O(13),O(14),O(15),

// rate 15
O(16),O(16),O(16),O(16),

// 32 dummy rates (same as 15 3)
O(16),O(16),O(16),O(16),O(16),O(16),O(16),O(16),
O(16),O(16),O(16),O(16),O(16),O(16),O(16),O(16),
O(16),O(16),O(16),O(16),O(16),O(16),O(16),O(16),
O(16),O(16),O(16),O(16),O(16),O(16),O(16),O(16)
};

// rate  0,    1,    2,   3,   4,   5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15
// shift 11,   10,   9,   8,   7,   6,  5,  4,  3,  2, 1,  0,  0,  0,  0,  0
// mask  2047, 1023, 511, 255, 127, 63, 31, 15, 7,  3, 1,  0,  0,  0,  0,  0
static constexpr std::array<uint8_t, 32 + 64 + 32> eg_rate_shift = {
// Envelope Generator counter shifts (32 + 64 rates + 32 RKS)
// 32 infinite time rates
   0,  0,  0,  0,  0,  0,  0,  0,
   0,  0,  0,  0,  0,  0,  0,  0,
   0,  0,  0,  0,  0,  0,  0,  0,
   0,  0,  0,  0,  0,  0,  0,  0,

// rates 00-11
  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,
   0,  0,  0,  0,

// rate 12
   0,  0,  0,  0,

// rate 13
   0,  0,  0,  0,

// rate 14
   0,  0,  0,  0,

// rate 15
   0,  0,  0,  0,

// 32 dummy rates (same as 15 3)
   0,  0,  0,  0,  0,  0,  0,  0,
   0,  0,  0,  0,  0,  0,  0,  0,
   0,  0,  0,  0,  0,  0,  0,  0,
   0,  0,  0,  0,  0,  0,  0,  0
};

// DT2 defines offset in cents from base note
//
// This table defines offset in frequency-deltas table.
// User's Manual page 22
//
// Values below were calculated using formula: value =  orig.val / 1.5625
//
// DT2=0 DT2=1 DT2=2 DT2=3
// 0     600   781   950
static constexpr std::array<unsigned, 4> dt2_tab = {0, 384, 500, 608};

// DT1 defines offset in Hertz from base note
// This table is converted while initialization...
// Detune table shown in YM2151 User's Manual is wrong (verified on the real chip)
static constexpr std::array<uint8_t, 4 * 32> dt1_tab = {
// DT1 = 0
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

// DT1 = 1
  0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2,
  2, 3, 3, 3, 4, 4, 4, 5, 5, 6, 6, 7, 8, 8, 8, 8,

// DT1 = 2
  1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5,
  5, 6, 6, 7, 8, 8, 9,10,11,12,13,14,16,16,16,16,

// DT1 = 3
  2, 2, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 6, 6, 7,
  8, 8, 9,10,11,12,13,14,16,17,19,20,22,22,22,22
};

static constexpr std::array<uint16_t, 768> phaseInc_rom = {
1299,1300,1301,1302,1303,1304,1305,1306,1308,1309,1310,1311,1313,1314,1315,1316,
1318,1319,1320,1321,1322,1323,1324,1325,1327,1328,1329,1330,1332,1333,1334,1335,
1337,1338,1339,1340,1341,1342,1343,1344,1346,1347,1348,1349,1351,1352,1353,1354,
1356,1357,1358,1359,1361,1362,1363,1364,1366,1367,1368,1369,1371,1372,1373,1374,
1376,1377,1378,1379,1381,1382,1383,1384,1386,1387,1388,1389,1391,1392,1393,1394,
1396,1397,1398,1399,1401,1402,1403,1404,1406,1407,1408,1409,1411,1412,1413,1414,
1416,1417,1418,1419,1421,1422,1423,1424,1426,1427,1429,1430,1431,1432,1434,1435,
1437,1438,1439,1440,1442,1443,1444,1445,1447,1448,1449,1450,1452,1453,1454,1455,
1458,1459,1460,1461,1463,1464,1465,1466,1468,1469,1471,1472,1473,1474,1476,1477,
1479,1480,1481,1482,1484,1485,1486,1487,1489,1490,1492,1493,1494,1495,1497,1498,
1501,1502,1503,1504,1506,1507,1509,1510,1512,1513,1514,1515,1517,1518,1520,1521,
1523,1524,1525,1526,1528,1529,1531,1532,1534,1535,1536,1537,1539,1540,1542,1543,
1545,1546,1547,1548,1550,1551,1553,1554,1556,1557,1558,1559,1561,1562,1564,1565,
1567,1568,1569,1570,1572,1573,1575,1576,1578,1579,1580,1581,1583,1584,1586,1587,
1590,1591,1592,1593,1595,1596,1598,1599,1601,1602,1604,1605,1607,1608,1609,1610,
1613,1614,1615,1616,1618,1619,1621,1622,1624,1625,1627,1628,1630,1631,1632,1633,
1637,1638,1639,1640,1642,1643,1645,1646,1648,1649,1651,1652,1654,1655,1656,1657,
1660,1661,1663,1664,1666,1667,1669,1670,1672,1673,1675,1676,1678,1679,1681,1682,
1685,1686,1688,1689,1691,1692,1694,1695,1697,1698,1700,1701,1703,1704,1706,1707,
1709,1710,1712,1713,1715,1716,1718,1719,1721,1722,1724,1725,1727,1728,1730,1731,
1734,1735,1737,1738,1740,1741,1743,1744,1746,1748,1749,1751,1752,1754,1755,1757,
1759,1760,1762,1763,1765,1766,1768,1769,1771,1773,1774,1776,1777,1779,1780,1782,
1785,1786,1788,1789,1791,1793,1794,1796,1798,1799,1801,1802,1804,1806,1807,1809,
1811,1812,1814,1815,1817,1819,1820,1822,1824,1825,1827,1828,1830,1832,1833,1835,
1837,1838,1840,1841,1843,1845,1846,1848,1850,1851,1853,1854,1856,1858,1859,1861,
1864,1865,1867,1868,1870,1872,1873,1875,1877,1879,1880,1882,1884,1885,1887,1888,
1891,1892,1894,1895,1897,1899,1900,1902,1904,1906,1907,1909,1911,1912,1914,1915,
1918,1919,1921,1923,1925,1926,1928,1930,1932,1933,1935,1937,1939,1940,1942,1944,
1946,1947,1949,1951,1953,1954,1956,1958,1960,1961,1963,1965,1967,1968,1970,1972,
1975,1976,1978,1980,1982,1983,1985,1987,1989,1990,1992,1994,1996,1997,1999,2001,
2003,2004,2006,2008,2010,2011,2013,2015,2017,2019,2021,2022,2024,2026,2028,2029,
2032,2033,2035,2037,2039,2041,2043,2044,2047,2048,2050,2052,2054,2056,2058,2059,
2062,2063,2065,2067,2069,2071,2073,2074,2077,2078,2080,2082,2084,2086,2088,2089,
2092,2093,2095,2097,2099,2101,2103,2104,2107,2108,2110,2112,2114,2116,2118,2119,
2122,2123,2125,2127,2129,2131,2133,2134,2137,2139,2141,2142,2145,2146,2148,2150,
2153,2154,2156,2158,2160,2162,2164,2165,2168,2170,2172,2173,2176,2177,2179,2181,
2185,2186,2188,2190,2192,2194,2196,2197,2200,2202,2204,2205,2208,2209,2211,2213,
2216,2218,2220,2222,2223,2226,2227,2230,2232,2234,2236,2238,2239,2242,2243,2246,
2249,2251,2253,2255,2256,2259,2260,2263,2265,2267,2269,2271,2272,2275,2276,2279,
2281,2283,2285,2287,2288,2291,2292,2295,2297,2299,2301,2303,2304,2307,2308,2311,
2315,2317,2319,2321,2322,2325,2326,2329,2331,2333,2335,2337,2338,2341,2342,2345,
2348,2350,2352,2354,2355,2358,2359,2362,2364,2366,2368,2370,2371,2374,2375,2378,
2382,2384,2386,2388,2389,2392,2393,2396,2398,2400,2402,2404,2407,2410,2411,2414,
2417,2419,2421,2423,2424,2427,2428,2431,2433,2435,2437,2439,2442,2445,2446,2449,
2452,2454,2456,2458,2459,2462,2463,2466,2468,2470,2472,2474,2477,2480,2481,2484,
2488,2490,2492,2494,2495,2498,2499,2502,2504,2506,2508,2510,2513,2516,2517,2520,
2524,2526,2528,2530,2531,2534,2535,2538,2540,2542,2544,2546,2549,2552,2553,2556,
2561,2563,2565,2567,2568,2571,2572,2575,2577,2579,2581,2583,2586,2589,2590,2593
};

// Frequency-deltas to get the closest frequency possible.
// There are 11 octaves because of DT2 (max 950 cents over base frequency)
// and LFO phase modulation (max 800 cents below AND over base frequency)
// Summary:   octave  explanation
//             0       note code - LFO PM
//             1       note code
//             2       note code
//             3       note code
//             4       note code
//             5       note code
//             6       note code
//             7       note code
//             8       note code
//             9       note code + DT2 + LFO PM
//            10       note code + DT2 + LFO PM
static constexpr auto freq = [] {
	std::array<unsigned, 11 * 768> result = {}; // 11 octaves, 768 'cents' per octave

	// this loop calculates Hertz values for notes from c-0 to b-7
	// including 64 'cents' (100/64 that is 1.5625 of real cent) per note
	// i*100/64/1200 is equal to i/768

	// real chip works with 10 bits fixed point values (10.10)
	//   -10 because phaseInc_rom table values are already in 10.10 format
	double mult = 1 << (FREQ_SH - 10);

	for (auto i : xrange(768)) {
		double phaseInc = phaseInc_rom[i]; // real chip phase increment

		// octave 2 - reference octave
		//   adjust to X.10 fixed point
		result[768 + 2 * 768 + i] = int(phaseInc * mult) & 0xffffffc0;
		// octave 0 and octave 1
		for (auto j : xrange(2)) {
			// adjust to X.10 fixed point
			result[768 + j * 768 + i] = (result[768 + 2 * 768 + i] >> (2 - j)) & 0xffffffc0;
		}
		// octave 3 to 7
		for (auto j : xrange(3, 8)) {
			result[768 + j * 768 + i] = result[768 + 2 * 768 + i] << (j - 2);
		}
	}

	// octave -1 (all equal to: oct 0, _KC_00_, _KF_00_)
	for (auto i : xrange(768)) {
		result[0 * 768 + i] = result[1 * 768 + 0];
	}

	// octave 8 and 9 (all equal to: oct 7, _KC_14_, _KF_63_)
	for (auto j : xrange(8, 10)) {
		for (auto i : xrange(768)) {
			result[768 + j * 768 + i] = result[768 + 8 * 768 - 1];
		}
	}
	return result;
}();

// Frequency deltas for DT1. These deltas alter operator frequency
// after it has been taken from frequency-deltas table.
static constexpr auto dt1_freq = [] {
	std::array<int, 8 * 32> result = {};    // 8 DT1 levels, 32 KC values
	double mult = 1 << FREQ_SH;
	for (auto j : xrange(4)) {
		for (auto i : xrange(32)) {
			// calculate phase increment
			double phaseInc = double(dt1_tab[j * 32 + i]) / (1 << 20) * SIN_LEN;

			// positive and negative values
			result[(j + 0) * 32 + i] = int(phaseInc * mult);
			result[(j + 4) * 32 + i] = -result[(j + 0) * 32 + i];
		}
	}
	return result;
}();

// This table tells how many cycles/samples it takes before noise is recalculated.
// 2/2 means every cycle/sample, 2/5 means 2 out of 5 cycles/samples, etc.
static constexpr auto noise_tab = [] {
	std::array<int, 32> result = {};  // 17bit Noise Generator periods
	//for (auto [i, r] : enumerate(result)) { msvc bug
	for (int i = 0; i < 32; ++i) {
		result[i] = 32 - (i != 31 ? i : 30); // rate 30 and 31 are the same
	}
	return result;
}();

// Noise LFO waveform.
//
// Here are just 256 samples out of much longer data.
//
// It does NOT repeat every 256 samples on real chip and I wasn't able to find
// the point where it repeats (even in strings as long as 131072 samples).
//
// I only put it here because its better than nothing and perhaps
// someone might be able to figure out the real algorithm.
//
// Note that (due to the way the LFO output is calculated) it is quite
// possible that two values: 0x80 and 0x00 might be wrong in this table.
// To be exact:
// some 0x80 could be 0x81 as well as some 0x00 could be 0x01.
static constexpr std::array<uint8_t, 256> lfo_noise_waveform = {
0xFF,0xEE,0xD3,0x80,0x58,0xDA,0x7F,0x94,0x9E,0xE3,0xFA,0x00,0x4D,0xFA,0xFF,0x6A,
0x7A,0xDE,0x49,0xF6,0x00,0x33,0xBB,0x63,0x91,0x60,0x51,0xFF,0x00,0xD8,0x7F,0xDE,
0xDC,0x73,0x21,0x85,0xB2,0x9C,0x5D,0x24,0xCD,0x91,0x9E,0x76,0x7F,0x20,0xFB,0xF3,
0x00,0xA6,0x3E,0x42,0x27,0x69,0xAE,0x33,0x45,0x44,0x11,0x41,0x72,0x73,0xDF,0xA2,

0x32,0xBD,0x7E,0xA8,0x13,0xEB,0xD3,0x15,0xDD,0xFB,0xC9,0x9D,0x61,0x2F,0xBE,0x9D,
0x23,0x65,0x51,0x6A,0x84,0xF9,0xC9,0xD7,0x23,0xBF,0x65,0x19,0xDC,0x03,0xF3,0x24,
0x33,0xB6,0x1E,0x57,0x5C,0xAC,0x25,0x89,0x4D,0xC5,0x9C,0x99,0x15,0x07,0xCF,0xBA,
0xC5,0x9B,0x15,0x4D,0x8D,0x2A,0x1E,0x1F,0xEA,0x2B,0x2F,0x64,0xA9,0x50,0x3D,0xAB,

0x50,0x77,0xE9,0xC0,0xAC,0x6D,0x3F,0xCA,0xCF,0x71,0x7D,0x80,0xA6,0xFD,0xFF,0xB5,
0xBD,0x6F,0x24,0x7B,0x00,0x99,0x5D,0xB1,0x48,0xB0,0x28,0x7F,0x80,0xEC,0xBF,0x6F,
0x6E,0x39,0x90,0x42,0xD9,0x4E,0x2E,0x12,0x66,0xC8,0xCF,0x3B,0x3F,0x10,0x7D,0x79,
0x00,0xD3,0x1F,0x21,0x93,0x34,0xD7,0x19,0x22,0xA2,0x08,0x20,0xB9,0xB9,0xEF,0x51,

0x99,0xDE,0xBF,0xD4,0x09,0x75,0xE9,0x8A,0xEE,0xFD,0xE4,0x4E,0x30,0x17,0xDF,0xCE,
0x11,0xB2,0x28,0x35,0xC2,0x7C,0x64,0xEB,0x91,0x5F,0x32,0x0C,0x6E,0x00,0xF9,0x92,
0x19,0xDB,0x8F,0xAB,0xAE,0xD6,0x12,0xC4,0x26,0x62,0xCE,0xCC,0x0A,0x03,0xE7,0xDD,
0xE2,0x4D,0x8A,0xA6,0x46,0x95,0x0F,0x8F,0xF5,0x15,0x97,0x32,0xD4,0x28,0x1E,0x55
};

void YM2151::keyOn(YM2151Operator& op, unsigned keySet) const
{
	if (!op.key) {
		op.phase = 0; /* clear phase */
		op.state = EG_ATT; /* KEY ON = attack */
		op.volume += (~op.volume *
		          (eg_inc[op.eg_sel_ar + ((eg_cnt >> op.eg_sh_ar)&7)])
		         ) >>4;
		if (op.volume <= MIN_ATT_INDEX) {
			op.volume = MIN_ATT_INDEX;
			op.state = EG_DEC;
		}
	}
	op.key |= keySet;
}

void YM2151::keyOff(YM2151Operator& op, unsigned keyClear) const
{
	if (op.key) {
		op.key &= keyClear;
		if (!op.key && (op.state > EG_REL)) {
			op.state = EG_REL; // KEY OFF = release
		}
	}
}

void YM2151::envelopeKONKOFF(std::span<YM2151Operator, 4> op, int v) const
{
	if (v & 0x08) { // M1
		keyOn (op[0], 1);
	} else {
		keyOff(op[0], unsigned(~1));
	}
	if (v & 0x20) { // M2
		keyOn (op[1], 1);
	} else {
		keyOff(op[1], unsigned(~1));
	}
	if (v & 0x10) { // C1
		keyOn (op[2], 1);
	} else {
		keyOff(op[2], unsigned(~1));
	}
	if (v & 0x40) { // C2
		keyOn (op[3], 1);
	} else {
		keyOff(op[3], unsigned(~1));
	}
}

void YM2151::setConnect(std::span<YM2151Operator, 4> o, int cha, int v)
{
	YM2151Operator& om1 = o[0];
	YM2151Operator& om2 = o[1];
	YM2151Operator& oc1 = o[2];

	// set connect algorithm
	// MEM is simply one sample delay
	switch (v & 7) {
	case 0:
		// M1---C1---MEM---M2---C2---OUT
		om1.connect = &c1;
		oc1.connect = &mem;
		om2.connect = &c2;
		om1.mem_connect = &m2;
		break;

	case 1:
		// M1------+-MEM---M2---C2---OUT
		//      C1-+
		om1.connect = &mem;
		oc1.connect = &mem;
		om2.connect = &c2;
		om1.mem_connect = &m2;
		break;

	case 2:
		// M1-----------------+-C2---OUT
		//      C1---MEM---M2-+
		om1.connect = &c2;
		oc1.connect = &mem;
		om2.connect = &c2;
		om1.mem_connect = &m2;
		break;

	case 3:
		// M1---C1---MEM------+-C2---OUT
		//                 M2-+
		om1.connect = &c1;
		oc1.connect = &mem;
		om2.connect = &c2;
		om1.mem_connect = &c2;
		break;

	case 4:
		// M1---C1-+-OUT
		// M2---C2-+
		// MEM: not used
		om1.connect = &c1;
		oc1.connect = &chanOut[cha];
		om2.connect = &c2;
		om1.mem_connect = &mem; // store it anywhere where it will not be used
		break;

	case 5:
		//    +----C1----+
		// M1-+-MEM---M2-+-OUT
		//    +----C2----+
		om1.connect = nullptr; // special mark
		oc1.connect = &chanOut[cha];
		om2.connect = &chanOut[cha];
		om1.mem_connect = &m2;
		break;

	case 6:
		// M1---C1-+
		//      M2-+-OUT
		//      C2-+
		// MEM: not used
		om1.connect = &c1;
		oc1.connect = &chanOut[cha];
		om2.connect = &chanOut[cha];
		om1.mem_connect = &mem; // store it anywhere where it will not be used
		break;

	case 7:
		// M1-+
		// C1-+-OUT
		// M2-+
		// C2-+
		// MEM: not used
		om1.connect = &chanOut[cha];
		oc1.connect = &chanOut[cha];
		om2.connect = &chanOut[cha];
		om1.mem_connect = &mem; // store it anywhere where it will not be used
		break;
	}
}

void YM2151::refreshEG(std::span<YM2151Operator, 4> op)
{
	unsigned kc = op[0].kc;

	// v = 32 + 2*RATE + RKS = max 126
	unsigned v = kc >> op[0].ks;
	if ((op[0].ar + v) < 32 + 62) {
		op[0].eg_sh_ar  = eg_rate_shift [op[0].ar + v];
		op[0].eg_sel_ar = eg_rate_select[op[0].ar + v];
	} else {
		op[0].eg_sh_ar  = 0;
		op[0].eg_sel_ar = 17 * RATE_STEPS;
	}
	op[0].eg_sh_d1r  = eg_rate_shift [op[0].d1r + v];
	op[0].eg_sel_d1r = eg_rate_select[op[0].d1r + v];
	op[0].eg_sh_d2r  = eg_rate_shift [op[0].d2r + v];
	op[0].eg_sel_d2r = eg_rate_select[op[0].d2r + v];
	op[0].eg_sh_rr   = eg_rate_shift [op[0].rr  + v];
	op[0].eg_sel_rr  = eg_rate_select[op[0].rr  + v];

	v = kc >> op[1].ks;
	if ((op[1].ar + v) < 32 + 62) {
		op[1].eg_sh_ar  = eg_rate_shift [op[1].ar + v];
		op[1].eg_sel_ar = eg_rate_select[op[1].ar + v];
	} else {
		op[1].eg_sh_ar  = 0;
		op[1].eg_sel_ar = 17 * RATE_STEPS;
	}
	op[1].eg_sh_d1r  = eg_rate_shift [op[1].d1r + v];
	op[1].eg_sel_d1r = eg_rate_select[op[1].d1r + v];
	op[1].eg_sh_d2r  = eg_rate_shift [op[1].d2r + v];
	op[1].eg_sel_d2r = eg_rate_select[op[1].d2r + v];
	op[1].eg_sh_rr   = eg_rate_shift [op[1].rr  + v];
	op[1].eg_sel_rr  = eg_rate_select[op[1].rr  + v];

	v = kc >> op[2].ks;
	if ((op[2].ar + v) < 32 + 62) {
		op[2].eg_sh_ar  = eg_rate_shift [op[2].ar + v];
		op[2].eg_sel_ar = eg_rate_select[op[2].ar + v];
	} else {
		op[2].eg_sh_ar  = 0;
		op[2].eg_sel_ar = 17 * RATE_STEPS;
	}
	op[2].eg_sh_d1r  = eg_rate_shift [op[2].d1r + v];
	op[2].eg_sel_d1r = eg_rate_select[op[2].d1r + v];
	op[2].eg_sh_d2r  = eg_rate_shift [op[2].d2r + v];
	op[2].eg_sel_d2r = eg_rate_select[op[2].d2r + v];
	op[2].eg_sh_rr   = eg_rate_shift [op[2].rr  + v];
	op[2].eg_sel_rr  = eg_rate_select[op[2].rr  + v];

	v = kc >> op[3].ks;
	if ((op[3].ar + v) < 32 + 62) {
		op[3].eg_sh_ar  = eg_rate_shift [op[3].ar + v];
		op[3].eg_sel_ar = eg_rate_select[op[3].ar + v];
	} else {
		op[3].eg_sh_ar  = 0;
		op[3].eg_sel_ar = 17 * RATE_STEPS;
	}
	op[3].eg_sh_d1r  = eg_rate_shift [op[3].d1r + v];
	op[3].eg_sel_d1r = eg_rate_select[op[3].d1r + v];
	op[3].eg_sh_d2r  = eg_rate_shift [op[3].d2r + v];
	op[3].eg_sel_d2r = eg_rate_select[op[3].d2r + v];
	op[3].eg_sh_rr   = eg_rate_shift [op[3].rr  + v];
	op[3].eg_sel_rr  = eg_rate_select[op[3].rr  + v];
}

void YM2151::writeReg(uint8_t r, uint8_t v, EmuTime time)
{
	updateStream(time);

	YM2151Operator& op = oper[(r & 0x07) * 4 + ((r & 0x18) >> 3)];

	regs[r] = v;
	switch (r & 0xe0) {
	case 0x00:
		switch (r) {
		case 0x01:
		case 0x09:
			// the test register is located differently between the variants
			if ((r == 1 && variant == Variant::YM2151) ||
		            (r == 9 && variant == Variant::YM2164)) {
				test = v;
				if (v & 2) lfo_phase = 0; // bit 1: LFO reset
			}
			break;

		case 0x08:
			envelopeKONKOFF(subspan<4>(oper, 4 * (v & 7)), v);
			break;

		case 0x0f: // noise mode enable, noise period
			noise = v;
			noise_f = noise_tab[v & 0x1f];
			noise_p = 0;
			break;

		case 0x10:
			timer_A_val &= 0x03;
			timer_A_val |= v << 2;
			timer1->setValue(timer_A_val);
			break;

		case 0x11:
			timer_A_val &= 0x03fc;
			timer_A_val |= v & 3;
			timer1->setValue(timer_A_val);
			break;

		case 0x12:
			timer2->setValue(v);
			break;

		case 0x14: // CSM, irq flag reset, irq enable, timer start/stop
			irq_enable = v; // bit 3-timer B, bit 2-timer A, bit 7 - CSM
			if (v & 0x10) { // reset timer A irq flag
				resetStatus(1);
			}
			if (v & 0x20) { // reset timer B irq flag
				resetStatus(2);
			}
			timer1->setStart((v & 4) != 0, time);
			timer2->setStart((v & 8) != 0, time);
			break;

		case 0x18: // LFO frequency
			lfo_overflow = (1 << ((15 - (v >> 4)) + 3));
			lfo_counter_add = 0x10 + (v & 0x0f);
			break;

		case 0x19: // PMD (bit 7==1) or AMD (bit 7==0)
			if (v & 0x80) {
				pmd = narrow<int8_t>(v & 0x7f);
			} else {
				amd = v & 0x7f;
			}
			break;

		case 0x1b: // CT2, CT1, LFO waveform
			ct = v >> 6;
			lfo_wsel = v & 3;
			// TODO ym2151WritePortCallback(0 , ct);
			break;

		default:
			break;
		}
		break;

	case 0x20: {
		auto o = subspan<4>(oper, 4 * (r & 7));
		switch (r & 0x18) {
		case 0x00: // RL enable, Feedback, Connection
			o[0].fb_shift = ((v >> 3) & 7) ? ((v >> 3) & 7) + 6 : 0;
			pan[(r & 7) * 2 + 0] = (v & 0x40) ? ~0 : 0;
			pan[(r & 7) * 2 + 1] = (v & 0x80) ? ~0 : 0;
			setConnect(o, r & 7, v & 7);
			break;

		case 0x08: // Key Code
			v &= 0x7f;
			if (v != o[0].kc) {
				unsigned kc_channel = (v - (v>>2))*64;
				kc_channel += 768;
				kc_channel |= (o[0].kc_i & 63);

				o[0].kc   = v;
				o[0].kc_i = kc_channel;
				o[1].kc   = v;
				o[1].kc_i = kc_channel;
				o[2].kc   = v;
				o[2].kc_i = kc_channel;
				o[3].kc   = v;
				o[3].kc_i = kc_channel;

				unsigned kc = v>>2;
				o[0].dt1 = dt1_freq[o[0].dt1_i + kc];
				o[0].freq = ((freq[kc_channel + o[0].dt2] + o[0].dt1) * o[0].mul) >> 1;

				o[1].dt1 = dt1_freq[o[1].dt1_i + kc];
				o[1].freq = ((freq[kc_channel + o[1].dt2] + o[1].dt1) * o[1].mul) >> 1;

				o[2].dt1 = dt1_freq[o[2].dt1_i + kc];
				o[2].freq = ((freq[kc_channel + o[2].dt2] + o[2].dt1) * o[2].mul) >> 1;

				o[3].dt1 = dt1_freq[o[3].dt1_i + kc];
				o[3].freq = ((freq[kc_channel + o[3].dt2] + o[3].dt1) * o[3].mul) >> 1;

				refreshEG(o);
			}
			break;

		case 0x10: // Key Fraction
			v >>= 2;
			if (v != (o[0].kc_i & 63)) {
				unsigned kc_channel = v;
				kc_channel |= (o[0].kc_i & ~63);

				o[0].kc_i = kc_channel;
				o[1].kc_i = kc_channel;
				o[2].kc_i = kc_channel;
				o[3].kc_i = kc_channel;

				o[0].freq = ((freq[kc_channel + o[0].dt2] + o[0].dt1) * o[0].mul) >> 1;
				o[1].freq = ((freq[kc_channel + o[1].dt2] + o[1].dt1) * o[1].mul) >> 1;
				o[2].freq = ((freq[kc_channel + o[2].dt2] + o[2].dt1) * o[2].mul) >> 1;
				o[3].freq = ((freq[kc_channel + o[3].dt2] + o[3].dt1) * o[3].mul) >> 1;
			}
			break;

		case 0x18: // PMS, AMS
			o[0].pms = narrow<int8_t>((v >> 4) & 7);
			o[0].ams = (v & 3);
			break;
		}
		break;
	}
	case 0x40: { // DT1, MUL
		unsigned olddt1_i = op.dt1_i;
		unsigned oldMul = op.mul;

		op.dt1_i = (v & 0x70) << 1;
		op.mul   = (v & 0x0f) ? (v & 0x0f) << 1 : 1;

		if (olddt1_i != op.dt1_i) {
			op.dt1 = dt1_freq[op.dt1_i + (op.kc>>2)];
		}
		if ((olddt1_i != op.dt1_i) || (oldMul != op.mul)) {
			op.freq = ((freq[op.kc_i + op.dt2] + op.dt1) * op.mul) >> 1;
		}
		break;
	}
	case 0x60: // TL
		op.tl = (v & 0x7f) << (ENV_BITS - 7); // 7bit TL
		break;

	case 0x80: { // KS, AR
		unsigned oldKs = op.ks;
		unsigned oldAr = op.ar;
		op.ks = 5 - (v >> 6);
		op.ar = (v & 0x1f) ? 32 + ((v & 0x1f) << 1) : 0;

		if ((op.ar != oldAr) || (op.ks != oldKs)) {
			if ((op.ar + (op.kc >> op.ks)) < 32 + 62) {
				op.eg_sh_ar  = eg_rate_shift [op.ar + (op.kc>>op.ks)];
				op.eg_sel_ar = eg_rate_select[op.ar + (op.kc>>op.ks)];
			} else {
				op.eg_sh_ar  = 0;
				op.eg_sel_ar = 17 * RATE_STEPS;
			}
		}
		if (op.ks != oldKs) {
			op.eg_sh_d1r  = eg_rate_shift [op.d1r + (op.kc >> op.ks)];
			op.eg_sel_d1r = eg_rate_select[op.d1r + (op.kc >> op.ks)];
			op.eg_sh_d2r  = eg_rate_shift [op.d2r + (op.kc >> op.ks)];
			op.eg_sel_d2r = eg_rate_select[op.d2r + (op.kc >> op.ks)];
			op.eg_sh_rr   = eg_rate_shift [op.rr  + (op.kc >> op.ks)];
			op.eg_sel_rr  = eg_rate_select[op.rr  + (op.kc >> op.ks)];
		}
		break;
	}
	case 0xa0: // LFO AM enable, D1R
		op.AMmask = (v & 0x80) ? ~0 : 0;
		op.d1r    = (v & 0x1f) ? 32 + ((v & 0x1f) << 1) : 0;
		op.eg_sh_d1r  = eg_rate_shift [op.d1r + (op.kc >> op.ks)];
		op.eg_sel_d1r = eg_rate_select[op.d1r + (op.kc >> op.ks)];
		break;

	case 0xc0: { // DT2, D2R
		unsigned olddt2 = op.dt2;
		op.dt2 = dt2_tab[v >> 6];
		if (op.dt2 != olddt2) {
			op.freq = ((freq[op.kc_i + op.dt2] + op.dt1) * op.mul) >> 1;
		}
		op.d2r = (v & 0x1f) ? 32 + ((v & 0x1f) << 1) : 0;
		op.eg_sh_d2r  = eg_rate_shift [op.d2r + (op.kc >> op.ks)];
		op.eg_sel_d2r = eg_rate_select[op.d2r + (op.kc >> op.ks)];
		break;
	}
	case 0xe0: // D1L, RR
		op.d1l = d1l_tab[v >> 4];
		op.rr  = 34 + ((v & 0x0f) << 2);
		op.eg_sh_rr  = eg_rate_shift [op.rr + (op.kc >> op.ks)];
		op.eg_sel_rr = eg_rate_select[op.rr + (op.kc >> op.ks)];
		break;
	}
}

static constexpr auto INPUT_RATE = unsigned(cstd::round(3579545 / 64.0));

YM2151::YM2151(const std::string& name_, static_string_view desc,
               const DeviceConfig& config, EmuTime time, Variant variant_)
	: ResampledSoundDevice(config.getMotherBoard(), name_, desc, 8, INPUT_RATE, true)
	, irq(config.getMotherBoard(), getName() + ".IRQ")
	, timer1(EmuTimer::createOPM_1(config.getScheduler(), *this))
	, timer2(variant_ == Variant::YM2164 ? EmuTimer::createOPP_2(config.getScheduler(), *this)
					     : EmuTimer::createOPM_2(config.getScheduler(), *this))
	, variant(variant_)
{
	// TODO Registers 0x20-0xFF are cleared on reset.
	//      Should we do the same for registers 0x00-0x1F?

	if (false) {
		std::cout << "tl_tab:";
		for (const auto& e : tl_tab) std::cout << ' ' << e;
		std::cout << '\n';

		std::cout << "sin_tab:";
		for (const auto& e : sin_tab) std::cout << ' ' << e;
		std::cout << '\n';

		std::cout << "d1l_tab:";
		for (const auto& e : d1l_tab) std::cout << ' ' << e;
		std::cout << '\n';

		std::cout << "freq:";
		for (const auto& e : freq) std::cout << ' ' << e;
		std::cout << '\n';

		std::cout << "dt1_freq:";
		for (const auto& e : dt1_freq) std::cout << ' ' << e;
		std::cout << '\n';

		std::cout << "noise_tab:";
		for (const auto& e : noise_tab) std::cout << ' ' << e;
		std::cout << '\n';
	}

	reset(time);

	registerSound(config);
}

YM2151::~YM2151()
{
	unregisterSound();
}

bool YM2151::checkMuteHelper()
{
	return std::ranges::all_of(oper, [](auto& op) { return op.state == EG_OFF; });
}

void YM2151::reset(EmuTime time)
{
	// initialize hardware registers
	for (auto& op : oper) {
		memset(&op, '\0', sizeof(op));
		op.volume = MAX_ATT_INDEX;
		op.kc_i = 768; // min kc_i value
	}

	eg_timer = 0;
	eg_cnt   = 0;

	lfo_timer   = 0;
	lfo_counter = 0;
	lfo_phase   = 0;
	lfo_wsel    = 0;
	pmd = 0;
	amd = 0;
	lfa = 0;
	lfp = 0;

	test = 0;

	irq_enable = 0;
	timer1->setStart(false, time);
	timer2->setStart(false, time);

	noise     = 0;
	noise_rng = 0;
	noise_p   = 0;
	noise_f   = noise_tab[0];

	csm_req = 0;
	status  = 0;

	writeReg(0x1b, 0, time); // only because of CT1, CT2 output pins
	writeReg(0x18, 0, time); // set LFO frequency
	for (auto i : xrange(0x20, 0x100)) { // set the operators
		writeReg(narrow<uint8_t>(i), 0, time);
	}

	irq.reset();
}

int YM2151::opCalc(const YM2151Operator& op, unsigned env, int pm) const
{
	unsigned p = (env << 3) + sin_tab[(int((op.phase & ~FREQ_MASK) + (pm << 15)) >> FREQ_SH) & SIN_MASK];
	if (p >= TL_TAB_LEN) {
		return 0;
	}
	return tl_tab[p];
}

int YM2151::opCalc1(const YM2151Operator& op, unsigned env, int pm) const
{
	int i = (narrow_cast<int>(op.phase) & ~FREQ_MASK) + pm;
	unsigned p = (env << 3) + sin_tab[(i >> FREQ_SH) & SIN_MASK];
	if (p >= TL_TAB_LEN) {
		return 0;
	}
	return tl_tab[p];
}

unsigned YM2151::volumeCalc(const YM2151Operator& op, unsigned AM) const
{
	return op.tl + unsigned(op.volume) + (AM & op.AMmask);
}

void YM2151::chanCalc(unsigned chan)
{
	m2 = c1 = c2 = mem = 0;
	auto op = subspan<4>(oper, 4 * chan); // M1
	*op[0].mem_connect = op[0].mem_value; // restore delayed sample (MEM) value to m2 or c2

	unsigned AM = 0;
	if (op[0].ams) {
		AM = lfa << (op[0].ams-1);
	}
	unsigned env = volumeCalc(op[0], AM);
	{
		int out = op[0].fb_out_prev + op[0].fb_out_curr;
		op[0].fb_out_prev = op[0].fb_out_curr;

		if (!op[0].connect) {
			// algorithm 5
			mem = c1 = c2 = op[0].fb_out_prev;
		} else {
			*op[0].connect = op[0].fb_out_prev;
		}
		op[0].fb_out_curr = 0;
		if (env < ENV_QUIET) {
			if (!op[0].fb_shift) {
				out = 0;
			}
			op[0].fb_out_curr = opCalc1(op[0], env, (out << op[0].fb_shift));
		}
	}

	env = volumeCalc(op[1], AM); // M2
	if (env < ENV_QUIET) {
		*op[1].connect += opCalc(op[1], env, m2);
	}
	env = volumeCalc(op[2], AM); // C1
	if (env < ENV_QUIET) {
		*op[2].connect += opCalc(op[2], env, c1);
	}
	env = volumeCalc(op[3], AM); // C2
	if (env < ENV_QUIET) {
		chanOut[chan] += opCalc(op[3], env, c2);
	}
	// M1
	op[0].mem_value = mem;
}

void YM2151::chan7Calc()
{
	m2 = c1 = c2 = mem = 0;
	auto op = subspan<4>(oper, 4 * 7);

	*op[0].mem_connect = op[0].mem_value; // restore delayed sample (MEM) value to m2 or c2

	unsigned AM = 0;
	if (op[0].ams) {
		AM = lfa << (op[0].ams - 1);
	}
	unsigned env = volumeCalc(op[0], AM);
	{
		int out = op[0].fb_out_prev + op[0].fb_out_curr;
		op[0].fb_out_prev = op[0].fb_out_curr;

		if (!op[0].connect) {
			// algorithm 5
			mem = c1 = c2 = op[0].fb_out_prev;
		} else {
			// other algorithms
			*op[0].connect = op[0].fb_out_prev;
		}
		op[0].fb_out_curr = 0;
		if (env < ENV_QUIET) {
			if (!op[0].fb_shift) {
				out = 0;
			}
			op[0].fb_out_curr = opCalc1(op[0], env, (out << op[0].fb_shift));
		}
	}

	env = volumeCalc(op[1], AM); // M2
	if (env < ENV_QUIET) {
		*op[1].connect += opCalc(op[1], env, m2);
	}
	env = volumeCalc(op[2], AM); // C1
	if (env < ENV_QUIET) {
		*op[2].connect += opCalc(op[2], env, c1);
	}
	env = volumeCalc(op[3], AM); // C2
	if (noise & 0x80) {
		int noiseOut = 0;
		if (env < 0x3ff) {
			noiseOut = (narrow<int>(env) ^ 0x3ff) * 2; // range of the YM2151 noise output is -2044 to 2040
		}
		chanOut[7] += (noise_rng & 0x10000) ? noiseOut : -noiseOut; // bit 16 -> output
	} else {
		if (env < ENV_QUIET) {
			chanOut[7] += opCalc(op[3], env, c2);
		}
	}
	// M1
	op[0].mem_value = mem;
}

/*
The 'rate' is calculated from following formula (example on decay rate):
  rks = note-code after key scaling (a value from 0 to 31)
  DR = value written to the chip register
  rate = 2*DR + rks; (max rate = 2*31+31 = 93)
Four MSBs of the 'rate' above are the 'main' rate (from 00 to 15)
Two LSBs of the 'rate' above are the value 'x' (the shape type).
(eg. '11 2' means that 'rate' is 11*4+2=46)

NOTE: A 'sample' in the description below is actually 3 output samples,
thats because the Envelope Generator clock is equal to internal_clock/3.

Single '-' (minus) character in the diagrams below represents one sample
on the output; this is for rates 11 x (11 0, 11 1, 11 2 and 11 3)

these 'main' rates:
00 x: single '-' = 2048 samples; (ie. level can change every 2048 samples)
01 x: single '-' = 1024 samples;
02 x: single '-' = 512 samples;
03 x: single '-' = 256 samples;
04 x: single '-' = 128 samples;
05 x: single '-' = 64 samples;
06 x: single '-' = 32 samples;
07 x: single '-' = 16 samples;
08 x: single '-' = 8 samples;
09 x: single '-' = 4 samples;
10 x: single '-' = 2 samples;
11 x: single '-' = 1 sample; (ie. level can change every 1 sample)

Shapes for rates 11 x look like this:
rate:		step:
11 0        01234567

level:
0           --
1             --
2               --
3                 --

rate:		step:
11 1        01234567

level:
0           --
1             --
2               -
3                -
4                 --

rate:		step:
11 2        01234567

level:
0           --
1             -
2              -
3               --
4                 -
5                  -

rate:		step:
11 3        01234567

level:
0           --
1             -
2              -
3               -
4                -
5                 -
6                  -


For rates 12 x, 13 x, 14 x and 15 x output level changes on every
sample - this means that the waveform looks like this: (but the level
changes by different values on different steps)
12 3        01234567

0           -
2            -
4             -
8              -
10              -
12               -
14                -
18                 -
20                  -

Notes about the timing:
----------------------

1. Synchronism

Output level of each two (or more) voices running at the same 'main' rate
(eg 11 0 and 11 1 in the diagram below) will always be changing in sync,
even if there're started with some delay.

Note that, in the diagram below, the decay phase in channel 0 starts at
sample #2, while in channel 1 it starts at sample #6. Anyway, both channels
will always change their levels at exactly the same (following) samples.

(S - start point of this channel, A-attack phase, D-decay phase):

step:
01234567012345670123456

channel 0:
  --
 |  --
 |    -
 |     -
 |      --
 |        --
|           --
|             -
|              -
|               --
AADDDDDDDDDDDDDDDD
S

01234567012345670123456
channel 1:
      -
     | -
     |  --
     |    --
     |      --
     |        -
    |          -
    |           --
    |             --
    |               --
    AADDDDDDDDDDDDDDDD
    S
01234567012345670123456


2. Shifted (delayed) synchronism

Output of each two (or more) voices running at different 'main' rate
(9 1, 10 1 and 11 1 in the diagrams below) will always be changing
in 'delayed-sync' (even if there're started with some delay as in "1.")

Note that the shapes are delayed by exactly one sample per one 'main' rate
increment. (Normally one would expect them to start at the same samples.)

See diagram below (* - start point of the shape).

cycle:
0123456701234567012345670123456701234567012345670123456701234567

rate 09 1
*-------
        --------
                ----
                    ----
                        --------
                                *-------
                                |       --------
                                |               ----
                                |                   ----
                                |                       --------
rate 10 1                       |
--                              |
  *---                          |
      ----                      |
          --                    |
            --                  |
              ----              |
                  *---          |
                  |   ----      |
                  |       --    | | <- one step (two samples) delay between 9 1 and 10 1
                  |         --  | |
                  |           ----|
                  |               *---
                  |                   ----
                  |                       --
                  |                         --
                  |                           ----
rate 11 1         |
-                 |
 --               |
   *-             |
     --           |
       -          |
        -         |
         --       |
           *-     |
             --   |
               -  || <- one step (one sample) delay between 10 1 and 11 1
                - ||
                 --|
                   *-
                     --
                       -
                        -
                         --
                           *-
                             --
                               -
                                -
                                 --
*/

void YM2151::advanceEG()
{
	if (eg_timer++ != 3) {
		// envelope generator timer overflows every 3 samples (on real chip)
		return;
	}
	eg_timer = 0;
	eg_cnt++;

	// envelope generator
	for (auto& op : oper) {
		switch (op.state) {
		case EG_ATT: // attack phase
			if (!(eg_cnt & ((1 << op.eg_sh_ar) - 1))) {
				op.volume += (~op.volume *
						(eg_inc[op.eg_sel_ar + ((eg_cnt >> op.eg_sh_ar) & 7)])
					      ) >> 4;
				if (op.volume <= MIN_ATT_INDEX) {
					op.volume = MIN_ATT_INDEX;
					op.state = EG_DEC;
				}
			}
			break;

		case EG_DEC: // decay phase
			if (!(eg_cnt & ((1 << op.eg_sh_d1r) - 1))) {
				op.volume += eg_inc[op.eg_sel_d1r + ((eg_cnt >> op.eg_sh_d1r) & 7)];
				if (unsigned(op.volume) >= op.d1l) {
					op.state = EG_SUS;
				}
			}
			break;

		case EG_SUS: // sustain phase
			if (!(eg_cnt & ((1 << op.eg_sh_d2r) - 1))) {
				op.volume += eg_inc[op.eg_sel_d2r + ((eg_cnt >> op.eg_sh_d2r) & 7)];
				if (op.volume >= MAX_ATT_INDEX) {
					op.volume = MAX_ATT_INDEX;
					op.state = EG_OFF;
				}
			}
			break;

		case EG_REL: // release phase
			if (!(eg_cnt & ((1 << op.eg_sh_rr) - 1))) {
				op.volume += eg_inc[op.eg_sel_rr + ((eg_cnt >> op.eg_sh_rr) & 7)];
				if (op.volume >= MAX_ATT_INDEX) {
					op.volume = MAX_ATT_INDEX;
					op.state = EG_OFF;
				}
			}
			break;
		}
	}
}

void YM2151::advance()
{
	// LFO
	if (test & 2) {
		lfo_phase = 0;
	} else {
		if (lfo_timer++ >= lfo_overflow) {
			lfo_timer   = 0;
			lfo_counter += lfo_counter_add;
			lfo_phase   += (lfo_counter >> 4);
			lfo_phase   &= 255;
			lfo_counter &= 15;
		}
	}

	unsigned i = lfo_phase;
	// calculate LFO AM and PM waveform value (all verified on real chip,
	// except for noise algorithm which is impossible to analyze)
	auto [a, p] = [&] -> std::pair<int, int> {
		switch (lfo_wsel) {
		case 0:
			// saw
			// AM: 255 down to 0
			// PM: 0 to 127, -127 to 0 (at PMD=127: LFP = 0 to 126, -126 to 0)
			return {
				/*a =*/ (255 - i),
				/*p =*/ ((i < 128) ? i : (i - 255))
			};
		case 1:
			// square
			// AM: 255, 0
			// PM: 128,-128 (LFP = exactly +PMD, -PMD)
			return {
				/*a =*/ ((i < 128) ? 255 : 0),
				/*p =*/ ((i < 128) ? 128 : -128)
			};
		case 2:
			// triangle
			// AM: 255 down to 1 step -2; 0 up to 254 step +2
			// PM: 0 to  126 step +2,  127 to  1 step -2,
			//     0 to -126 step -2, -127 to -1 step +2
			return {
				/*a =*/ ((i < 128) ? (255 - (i * 2)) : ((i * 2) - 256)),
				/*p =*/ [&] {
						if (i < 64) {               // i = 0..63
							return i * 2;       //     0 to  126 step +2
						} else if (i < 128) {       // i = 64..127
							return 255 - i * 2; //   127 to    1 step -2
						} else if (i < 192) {       // i = 128..191
							return 256 - i * 2; //     0 to -126 step -2
						} else {                    // i = 192..255
							return i * 2 - 511; //  -127 to   -1 step +2
						}
					}()
			};
			break;
		case 3:
		default: // keep the compiler happy
			// Random. The real algorithm is unknown !!!
			// We just use a snapshot of data from real chip

			// AM: range 0 to 255
			// PM: range -128 to 127
			return {
				/*a =*/ lfo_noise_waveform[i],
				/*p =*/ (lfo_noise_waveform[i] - 128)
			};
		}
	}();
	lfa = a * amd / 128;
	lfp = p * pmd / 128;

	// The Noise Generator of the YM2151 is 17-bit shift register.
	// Input to the bit16 is negated (bit0 XOR bit3) (XNOR).
	// Output of the register is negated (bit0 XOR bit3).
	// Simply use bit16 as the noise output.

	// noise changes depending on the index in noise_tab (noise_f = noise_tab[x])
	// noise_tab contains how many cycles/samples (x2) the noise should change.
	// so, when it contains 29, noise should change every 14.5 cycles (2 out of 29).
	// if you read this code well, you'll see that is what happens here :)
	noise_p -= 2;
	if (noise_p < 0) {
		noise_p += noise_f;
		unsigned j = ((noise_rng ^ (noise_rng >> 3)) & 1) ^ 1;
		noise_rng = (j << 16) | (noise_rng >> 1);
	}

	// phase generator
	for (auto c : xrange(8)) {
		auto op = subspan<4>(oper, 4 * c);
		// only when phase modulation from LFO is enabled for this channel
		if (op[0].pms) {
			int mod_ind = lfp; // -128..+127 (8bits signed)
			if (op[0].pms < 6) {
				mod_ind >>= (6 - op[0].pms);
			} else {
				mod_ind <<= (op[0].pms - 5);
			}
			if (mod_ind) {
				unsigned kc_channel = op[0].kc_i + mod_ind;
				op[0].phase += ((freq[kc_channel + op[0].dt2] + op[0].dt1) * op[0].mul) >> 1;
				op[1].phase += ((freq[kc_channel + op[1].dt2] + op[1].dt1) * op[1].mul) >> 1;
				op[2].phase += ((freq[kc_channel + op[2].dt2] + op[2].dt1) * op[2].mul) >> 1;
				op[3].phase += ((freq[kc_channel + op[3].dt2] + op[3].dt1) * op[3].mul) >> 1;
			} else { // phase modulation from LFO is equal to zero
				op[0].phase += op[0].freq;
				op[1].phase += op[1].freq;
				op[2].phase += op[2].freq;
				op[3].phase += op[3].freq;
			}
		} else { // phase modulation from LFO is disabled
			op[0].phase += op[0].freq;
			op[1].phase += op[1].freq;
			op[2].phase += op[2].freq;
			op[3].phase += op[3].freq;
		}
	}

	// CSM is calculated *after* the phase generator calculations (verified
	// on real chip)
	// CSM keyon line seems to be ORed with the KO line inside of the chip.
	// The result is that it only works when KO (register 0x08) is off, ie. 0
	//
	// Interesting effect is that when timer A is set to 1023, the KEY ON happens
	// on every sample, so there is no KEY OFF at all - the result is that
	// the sound played is the same as after normal KEY ON.
	if (csm_req) { // CSM KEYON/KEYOFF sequence request
		if (csm_req == 2) { // KEY ON
			for (auto& op : oper) {
				keyOn(op, 2);
			}
			csm_req = 1;
		} else { // KEY OFF
			for (auto& op : oper) {
				keyOff(op, unsigned(~2));
			}
			csm_req = 0;
		}
	}
}

void YM2151::generateChannels(std::span<float*> bufs, unsigned num)
{
	if (checkMuteHelper()) {
		// TODO update internal state, even if muted
		std::ranges::fill(bufs, nullptr);
		return;
	}

	for (auto i : xrange(num)) {
		advanceEG();

		for (auto j : xrange(8 - 1)) {
			chanOut[j] = 0;
			chanCalc(j);
		}
		chanOut[7] = 0;
		chan7Calc(); // special case for channel 7

		for (auto j : xrange(8)) {
			bufs[j][2 * i + 0] += narrow_cast<float>(narrow_cast<int>(chanOut[j] & pan[2 * j + 0]));
			bufs[j][2 * i + 1] += narrow_cast<float>(narrow_cast<int>(chanOut[j] & pan[2 * j + 1]));
		}
		advance();
	}
}

void YM2151::callback(uint8_t flag)
{
	assert(flag == one_of(1, 2));
	setStatus(flag);

	if ((flag == 1) && (irq_enable & 0x80)) { // Timer 1
		csm_req = 2; // request KEY ON / KEY OFF sequence
	}
}

uint8_t YM2151::readStatus() const
{
	return status;
}

void YM2151::setStatus(uint8_t flags)
{
	status |= flags;
	auto enable = (irq_enable >> 2) & 3;
	if ((status & enable) != 0) {
		irq.set();
	}
}

void YM2151::resetStatus(uint8_t flags)
{
	status &= ~flags;
	auto enable = (irq_enable >> 2) & 3;
	if ((status & enable) == 0) {
		irq.reset();
	}
}


template<typename Archive>
void YM2151::YM2151Operator::serialize(Archive& a, unsigned /*version*/)
{
	//int* connect; // recalculated from regs[0x20-0x27]
	//int* mem_connect; // recalculated from regs[0x20-0x27]
	a.serialize("phase",       phase,
	            "freq",        freq,
	            "dt1",         dt1,
	            "mul",         mul,
	            "dt1_i",       dt1_i,
	            "dt2",         dt2,
	            "mem_value",   mem_value,
	            //"fb_shift",    fb_shift, // recalculated from regs[0x20-0x27]
	            "fb_out_curr", fb_out_curr,
	            "fb_out_prev", fb_out_prev,
	            "kc",          kc,
	            "kc_i",        kc_i,
	            "pms",         pms,
	            "ams",         ams,
	            "AMmask",      AMmask,
	            "state",       state,
	            "tl",          tl,
	            "volume",      volume,
	            "d1l",         d1l,
	            "key",         key,
	            "ks",          ks,
	            "ar",          ar,
	            "d1r",         d1r,
	            "d2r",         d2r,
	            "rr",          rr,
	            "eg_sh_ar",    eg_sh_ar,
	            "eg_sel_ar",   eg_sel_ar,
	            "eg_sh_d1r",   eg_sh_d1r,
	            "eg_sel_d1r",  eg_sel_d1r,
	            "eg_sh_d2r",   eg_sh_d2r,
	            "eg_sel_d2r",  eg_sel_d2r,
	            "eg_sh_rr",    eg_sh_rr,
	            "eg_sel_rr",   eg_sel_rr);
};

template<typename Archive>
void YM2151::serialize(Archive& a, unsigned /*version*/)
{
	a.serialize("irq",             irq,
	            "timer1",          *timer1,
	            "timer2",          *timer2,
	            "operators",       oper,
	            //"pan",             pan, // recalculated from regs[0x20-0x27]
	            "eg_cnt",          eg_cnt,
	            "eg_timer",        eg_timer,
	            "lfo_phase",       lfo_phase,
	            "lfo_timer",       lfo_timer,
	            "lfo_overflow",    lfo_overflow,
	            "lfo_counter",     lfo_counter,
	            "lfo_counter_add", lfo_counter_add,
	            "lfa",             lfa,
	            "lfp",             lfp,
	            "noise",           noise,
	            "noise_rng",       noise_rng,
	            "noise_p",         noise_p,
	            "noise_f",         noise_f,
	            "csm_req",         csm_req,
	            "irq_enable",      irq_enable,
	            "status",          status,
	            "chanout",         chanOut,
	            "m2",              m2,
	            "c1",              c1,
	            "c2",              c2,
	            "mem",             mem,
	            "timer_A_val",     timer_A_val,
	            "lfo_wsel",        lfo_wsel,
	            "amd",             amd,
	            "pmd",             pmd,
	            "test",            test,
	            "ct",              ct);
	a.serialize_blob("registers", regs);

	if constexpr (Archive::IS_LOADER) {
		// TODO restore more state from registers
		EmuTime time = timer1->getCurrentTime();
		for (auto r : xrange(uint8_t(0x20), uint8_t(0x28))) {
			writeReg(r , regs[r], time);
		}
	}
}
INSTANTIATE_SERIALIZE_METHODS(YM2151);

} // namespace openmsx