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https://github.com/ekeeke/Genesis-Plus-GX.git
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+fixed LFO implementation according to Nemesis description (UNTESTED, need feedback)
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ekeeke31
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@ -14,12 +14,13 @@
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**
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** 2006~2009 Eke-Eke (Genesis Plus GX):
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** Credits to Nemesis (@spritesmind.net), most of those fixes came from his tests on a Model 1 Sega Mega Drive
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** More informations here: http://gendev.spritesmind.net/forum/viewtopic.php?t=386
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**
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** - removed unused multichip support
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** - added YM2612 Context external access functions
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** - added LFO phase update in CH3 special mode (Warlock birds, Alladin bug sound)
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** - fixed internal timers emulation
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** - added Attack Rate immediate update on register write (Batman & Robin intro)
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** - implemented LFO phase update in CH3 special mode (Warlock birds, Alladin bug sound)
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** - improved internal timers emulation
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** - fixed Attack Rate update in some specific case (Batman & Robin intro)
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** - fixed EG behavior when Attack Rate is maximal
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** - fixed EG behavior when SL=0 (Mega Turrican tracks 03,09...) or/and Key ON occurs at minimal attenuation
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** - added EG output immediate update on register writes
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@ -29,6 +30,7 @@
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** - implemented correct SSG-EG emulation (Asterix, Beavis&Butthead, Bubba'n Six & many others)
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** - adjusted some EG rates
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** - modified address/data port behavior
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** - fixed LFO implementation (only 11 bits of precision)
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**
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** TODO: complete SSG-EG documentation
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**
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@ -582,9 +584,8 @@ typedef struct
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UINT32 eg_timer_add; /* step of eg_timer */
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UINT32 eg_timer_overflow; /* envelope generator timer overlfows every 3 samples (on real chip) */
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/* there are 2048 FNUMs that can be generated using FNUM/BLK registers
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but LFO works with one more bit of a precision so we really need 4096 elements */
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UINT32 fn_table[4096]; /* fnumber->increment counter */
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/* there are 2048 FNUMs that can be generated using FNUM/BLK registers */
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UINT32 fn_table[2048]; /* fnumber->increment counter */
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UINT32 fn_max; /* max increment (required for calculating phase overflow) */
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/* LFO */
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@ -1237,20 +1238,21 @@ INLINE void update_phase_lfo_slot(FM_SLOT *SLOT , INT32 pms, UINT32 block_fnum)
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{
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UINT32 fnum_lfo = ((block_fnum & 0x7f0) >> 4) * 32 * 8;
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INT32 lfo_fn_table_index_offset = lfo_pm_table[ fnum_lfo + pms + LFO_PM ];
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if (lfo_fn_table_index_offset) /* LFO phase modulation active */
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{
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block_fnum = block_fnum*2 + lfo_fn_table_index_offset;
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/* retrieve BLOCK register value */
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UINT8 blk = (block_fnum >> 11) & 7;
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UINT8 blk = (block_fnum&0x7000) >> 12;
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UINT32 fn = block_fnum & 0xfff;
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/* increase FNUM register value */
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UINT32 fn = (block_fnum + lfo_fn_table_index_offset) & 0x7ff;
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/* keyscale code */
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int kc = (blk<<2) | opn_fktable[fn >> 8];
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/* recalculate keyscale code */
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int kc = (blk<<2) | opn_fktable[fn >> 7];
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/* (frequency) phase increment counter */
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/* recalculate (frequency) phase increment counter */
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int fc = (ym2612.OPN.fn_table[fn]>>(7-blk)) + SLOT->DT[kc];
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/* (frequency) phase overflow (credits to Nemesis) */
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if (fc < 0) fc += ym2612.OPN.fn_max;
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@ -1266,21 +1268,22 @@ INLINE void update_phase_lfo_slot(FM_SLOT *SLOT , INT32 pms, UINT32 block_fnum)
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INLINE void update_phase_lfo_channel(FM_CH *CH)
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{
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UINT32 block_fnum = CH->block_fnum;
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UINT32 fnum_lfo = ((block_fnum & 0x7f0) >> 4) * 32 * 8;
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INT32 lfo_fn_table_index_offset = lfo_pm_table[ fnum_lfo + CH->pms + LFO_PM ];
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if (lfo_fn_table_index_offset) /* LFO phase modulation active */
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{
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block_fnum = block_fnum*2 + lfo_fn_table_index_offset;
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/* retrieve BLOCK register value */
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UINT8 blk = (block_fnum >> 11) & 7;
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UINT8 blk = (block_fnum&0x7000) >> 12;
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UINT32 fn = block_fnum & 0xfff;
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/* keyscale code */
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int kc = (blk<<2) | opn_fktable[fn >> 8];
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/* increase FNUM register value */
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UINT32 fn = (block_fnum + lfo_fn_table_index_offset)& 0x7ff;
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/* (frequency) phase increment counter */
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/* recalculate keyscale code */
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int kc = (blk<<2) | opn_fktable[fn >> 7];
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/* recalculate (frequency) phase increment counter */
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int fc = (ym2612.OPN.fn_table[fn]>>(7-blk));
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/* (frequency) phase overflow (credits to Nemesis) */
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@ -1316,7 +1319,6 @@ INLINE void chan_calc(FM_CH *CH)
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UINT32 AM = LFO_AM >> CH->ams;
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m2 = c1 = c2 = mem = 0;
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*CH->mem_connect = CH->mem_value; /* restore delayed sample (MEM) value to m2 or c2 */
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@ -1356,7 +1358,6 @@ INLINE void chan_calc(FM_CH *CH)
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if( eg_out < ENV_QUIET ) /* SLOT 4 */
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*CH->connect4 += op_calc(CH->SLOT[SLOT4].phase, eg_out, c2);
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/* store current MEM */
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CH->mem_value = mem;
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@ -1631,14 +1632,17 @@ static void OPNSetPres(int pres)
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/* make time tables */
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init_timetables(dt_tab);
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/* there are 2048 FNUMs that can be generated using FNUM/BLK registers
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but LFO works with one more bit of a precision so we really need 4096 elements */
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/* there are 2048 FNUMs that can be generated using FNUM/BLK registers */
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/* calculate fnumber -> increment counter table */
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for(i = 0; i < 4096; i++)
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for(i = 0; i < 2048; i++)
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{
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/* freq table for octave 7 */
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/* OPN phase increment counter = 20bit */
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ym2612.OPN.fn_table[i] = (UINT32)( (double)i * 32 * ym2612.OPN.ST.freqbase * (1<<(FREQ_SH-10)) ); /* -10 because chip works with 10.10 fixed point, while we use 16.16 */
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/* the correct formula is : F-Number = (144 * fnote * 2^20 / M) / 2^(B-1) */
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/* where sample clock is M/144 */
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/* this means the increment value for one clock sample is FNUM * 2^(B-1) = FNUM * 64 for octave 7 */
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/* we also need to handle the ratio between the chip frequency and the emulated frequency (can be 1.0) */
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ym2612.OPN.fn_table[i] = (UINT32)( (double)i * 64 * ym2612.OPN.ST.freqbase * (1<<(FREQ_SH-10)) ); /* -10 because chip works with 10.10 fixed point, while we use 16.16 */
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}
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/* maximal frequency is required for Phase overflow calculation, register size is 17 bits (Nemesis) */
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@ -1843,7 +1847,7 @@ INLINE void OPNWriteReg(int r, int v)
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/* keyscale code */
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CH->kcode = (blk<<2) | opn_fktable[fn >> 7];
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/* phase increment counter */
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CH->fc = ym2612.OPN.fn_table[fn*2]>>(7-blk);
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CH->fc = ym2612.OPN.fn_table[fn]>>(7-blk);
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/* store fnum in clear form for LFO PM calculations */
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CH->block_fnum = (blk<<11) | fn;
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@ -1862,7 +1866,7 @@ INLINE void OPNWriteReg(int r, int v)
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/* keyscale code */
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ym2612.OPN.SL3.kcode[c]= (blk<<2) | opn_fktable[fn >> 7];
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/* phase increment counter */
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ym2612.OPN.SL3.fc[c] = ym2612.OPN.fn_table[fn*2]>>(7-blk);
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ym2612.OPN.SL3.fc[c] = ym2612.OPN.fn_table[fn]>>(7-blk);
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ym2612.OPN.SL3.block_fnum[c] = (blk<<11) | fn; //fn;
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ym2612.CH[2].SLOT[SLOT1].Incr=-1;
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}
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