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[Core/CD] improved accuracy of CDC decoder processing (verified on re…
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…al hardware, cf. Krikzz's mcd-verificator)
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@ekeeke
ekeeke committed Feb 5, 2024
1 parent 904613f commit e8a6086
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Showing 8 changed files with 77 additions and 20 deletions.
1 change: 1 addition & 0 deletions HISTORY.txt
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Expand Up @@ -26,6 +26,7 @@ Genesis Plus GX 1.7.5 (xx/xx/xxxx) (Eke-Eke)
* improved accuracy of Main-CPU & Sub-CPU access to CDC registers (verified on real hardware, cf. Krikzz's mcd-verificator)
* improved accuracy of CDC data transfer to Main-CPU & Sub-CPU (verified on real hardware, cf. Krikzz's mcd-verificator)
* improved accuracy of CDC DMA processing (verified on real hardware, cf. Krikzz's mcd-verificator)
* improved accuracy of CDC decoder processing (verified on real hardware, cf. Krikzz's mcd-verificator)
* improved accuracy of CDC interrupt processing (verified on real hardware, cf. Krikzz's mcd-verificator)
* improved emulation of mirrored memory areas
* improved savestate format
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Binary file modified builds/genesis_plus_gx_libretro.dll
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Binary file modified builds/genplus_cube.dol
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Binary file modified builds/genplus_wii.dol
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70 changes: 62 additions & 8 deletions core/cd_hw/cdc.c
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Expand Up @@ -108,8 +108,8 @@ void cdc_reset(void)
cdc.head[1][2] = 0x00;
cdc.head[1][3] = 0x00;

/* reset CDC DMA cycle counter */
cdc.cycles = 0;
/* reset CDC DMA & decoder cycle counters */
cdc.cycles[0] = cdc.cycles[1] = 0;

/* disable CDC DMA */
cdc.dma_w = cdc.halted_dma_w = 0;
Expand Down Expand Up @@ -176,7 +176,6 @@ int cdc_context_save(uint8 *state)
save_param(&cdc.head, sizeof(cdc.head));
save_param(&cdc.stat, sizeof(cdc.stat));
save_param(&cdc.cycles, sizeof(cdc.cycles));
save_param(&cdc.dma_w, sizeof(cdc.dma_w));
save_param(&cdc.ram, sizeof(cdc.ram));
save_param(&tmp8, 1);

Expand All @@ -198,7 +197,6 @@ int cdc_context_load(uint8 *state)
load_param(&cdc.head, sizeof(cdc.head));
load_param(&cdc.stat, sizeof(cdc.stat));
load_param(&cdc.cycles, sizeof(cdc.cycles));
load_param(&cdc.dma_w, sizeof(cdc.dma_w));
load_param(&cdc.ram, sizeof(cdc.ram));

load_param(&tmp8, 1);
Expand Down Expand Up @@ -290,6 +288,16 @@ void cdc_dma_init(void)
/* Data Transfer End interrupt enabled ? */
if (cdc.ifctrl & BIT_DTEIEN)
{
/* check end of CDC decoder active period */
if ((cdc.irq & BIT_DECI) && (cdc.cycles[0] > cdc.cycles[1]))
{
/* clear pending decoder interrupt */
cdc.ifstat |= BIT_DECI;

/* update CDC IRQ state */
cdc.irq &= ~BIT_DECI;
}

/* level 5 interrupt triggered only on CDC /INT falling edge with interrupt enabled on gate-array side */
if (!cdc.irq && (scd.regs[0x32>>1].byte.l & 0x20))
{
Expand Down Expand Up @@ -380,7 +388,7 @@ void cdc_dma_init(void)
void cdc_dma_update(unsigned int cycles)
{
/* max number of bytes that can be transfered */
int dma_bytes = (cycles - cdc.cycles + DMA_CYCLES_PER_BYTE - 1) / DMA_CYCLES_PER_BYTE;
int dma_bytes = (cycles - cdc.cycles[0] + DMA_CYCLES_PER_BYTE - 1) / DMA_CYCLES_PER_BYTE;

/* always process blocks of 8 bytes */
dma_bytes = (dma_bytes / 8) * 8;
Expand All @@ -391,6 +399,9 @@ void cdc_dma_update(unsigned int cycles)
/* transfer remaining bytes using DMA */
cdc.dma_w(cdc.dbc.w + 1);

/* update DMA cycle counter */
cdc.cycles[0] += (cdc.dbc.w + 1) * DMA_CYCLES_PER_BYTE;

/* reset data byte counter (DBCH bits 4-7 should also be set to 1) */
cdc.dbc.w = 0xffff;

Expand All @@ -403,6 +414,16 @@ void cdc_dma_update(unsigned int cycles)
/* Data Transfer End interrupt enabled ? */
if (cdc.ifctrl & BIT_DTEIEN)
{
/* check end of CDC decoder active period */
if ((cdc.irq & BIT_DECI) && (cdc.cycles[0] > cdc.cycles[1]))
{
/* clear pending decoder interrupt */
cdc.ifstat |= BIT_DECI;

/* update CDC IRQ state */
cdc.irq &= ~BIT_DECI;
}

/* level 5 interrupt triggered only on CDC /INT falling edge with interrupt enabled on gate-array side*/
if (!cdc.irq && (scd.regs[0x32>>1].byte.l & 0x20))
{
Expand All @@ -424,7 +445,7 @@ void cdc_dma_update(unsigned int cycles)
if (s68k.stopped & (1<<0x04))
{
/* sync SUB-CPU with CDC DMA */
s68k.cycles = cdc.cycles;
s68k.cycles = cdc.cycles[0];

/* restart SUB-CPU */
s68k.stopped = 0;
Expand All @@ -445,7 +466,7 @@ void cdc_dma_update(unsigned int cycles)
cdc.dbc.w -= dma_bytes;

/* update DMA cycle counter */
cdc.cycles += dma_bytes * DMA_CYCLES_PER_BYTE;
cdc.cycles[0] += dma_bytes * DMA_CYCLES_PER_BYTE;
}
}

Expand All @@ -463,6 +484,9 @@ void cdc_decoder_update(uint32 header)
/* pending decoder interrupt */
cdc.ifstat &= ~BIT_DECI;

/* update CDC decoder end cycle (value adjusted for MCD-verificator CDC FLAGS Tests #40 & #41) */
cdc.cycles[1] = s68k.cycles + 269000;

/* decoder interrupt enabled ? */
if (cdc.ifctrl & BIT_DECIEN)
{
Expand Down Expand Up @@ -555,6 +579,16 @@ void cdc_reg_w(unsigned char data)
{
/* previous CDC IRQ state */
uint8 prev_irq = cdc.irq;

/* check end of CDC decoder active period */
if (s68k.cycles > cdc.cycles[1])
{
/* clear pending decoder interrupt */
cdc.ifstat |= BIT_DECI;

/* update previous CDC IRQ state */
prev_irq &= ~BIT_DECI;
}

/* update CDC IRQ state according to DTEIEN and DECIEN bits */
cdc.irq = ~cdc.ifstat & data & (BIT_DTEIEN | BIT_DECIEN);
Expand Down Expand Up @@ -614,7 +648,7 @@ void cdc_reg_w(unsigned char data)
cdc_dma_init();

/* initialize DMA cycle counter */
cdc.cycles = s68k.cycles;
cdc.cycles[0] = s68k.cycles;
}

break;
Expand Down Expand Up @@ -708,6 +742,16 @@ unsigned char cdc_reg_r(void)
{
case 0x01: /* IFSTAT */
{
/* check end of CDC decoder active period */
if (s68k.cycles > cdc.cycles[1])
{
/* clear pending decoder interrupt */
cdc.ifstat |= BIT_DECI;

/* update CDC IRQ state */
cdc.irq &= ~BIT_DECI;
}

data = cdc.ifstat;
break;
}
Expand Down Expand Up @@ -869,6 +913,16 @@ unsigned short cdc_host_r(uint8 cpu_access)
/* Data Transfer End interrupt enabled ? */
if (cdc.ifctrl & BIT_DTEIEN)
{
/* check end of CDC decoder active period */
if ((cdc.irq & BIT_DECI) && (cdc.cycles[0] > cdc.cycles[1]))
{
/* clear pending decoder interrupt */
cdc.ifstat |= BIT_DECI;

/* update CDC IRQ state */
cdc.irq &= ~BIT_DECI;
}

/* level 5 interrupt triggered only on CDC /INT falling edge with interrupt enabled on gate-array side */
if (!cdc.irq && (scd.regs[0x32>>1].byte.l & 0x20))
{
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2 changes: 1 addition & 1 deletion core/cd_hw/cdc.h
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Expand Up @@ -55,7 +55,7 @@ typedef struct
uint8 ctrl[2];
uint8 head[2][4];
uint8 stat[4];
unsigned int cycles;
int cycles[2];
void (*dma_w)(unsigned int length); /* active DMA callback */
void (*halted_dma_w)(unsigned int length); /* halted DMA callback */
uint8 ram[0x4000 + 2352]; /* 16K external RAM (with one block overhead to handle buffer overrun) */
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8 changes: 5 additions & 3 deletions core/cd_hw/scd.c
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Expand Up @@ -1983,9 +1983,11 @@ void scd_end_frame(unsigned int cycles)
/* adjust Stopwatch counter for next frame (can be negative) */
scd.stopwatch += (ticks * TIMERS_SCYCLES_RATIO) - cycles;

/* adjust SUB-CPU & GPU cycle counters for next frame */
s68k.cycles -= cycles;
gfx.cycles -= cycles;
/* adjust SUB-CPU, GPU and CDC cycle counters for next frame */
s68k.cycles -= cycles;
gfx.cycles -= cycles;
cdc.cycles[0] -= cycles;
cdc.cycles[1] -= cycles;

/* reset CPU registers polling */
m68k.poll.cycle = 0;
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16 changes: 8 additions & 8 deletions core/mem68k.c
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Expand Up @@ -788,9 +788,9 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
cdc.halted_dma_w = 0;

/* synchronize CDC DMA with MAIN-CPU (only if not already ahead) */
if (cdc.cycles < cycles)
if (cdc.cycles[0] < cycles)
{
cdc.cycles = cycles;
cdc.cycles[0] = cycles;
}
}
}
Expand Down Expand Up @@ -902,9 +902,9 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
cdc.halted_dma_w = 0;

/* synchronize CDC DMA with MAIN-CPU (only if not already ahead) */
if (cdc.cycles < cycles)
if (cdc.cycles[0] < cycles)
{
cdc.cycles = cycles;
cdc.cycles[0] = cycles;
}
}

Expand Down Expand Up @@ -1117,9 +1117,9 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
cdc.halted_dma_w = 0;

/* synchronize CDC DMA with MAIN-CPU (only if not already ahead) */
if (cdc.cycles < cycles)
if (cdc.cycles[0] < cycles)
{
cdc.cycles = cycles;
cdc.cycles[0] = cycles;
}
}
}
Expand Down Expand Up @@ -1241,9 +1241,9 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
cdc.halted_dma_w = 0;

/* synchronize CDC DMA with MAIN-CPU (only if not already ahead) */
if (cdc.cycles < cycles)
if (cdc.cycles[0] < cycles)
{
cdc.cycles = cycles;
cdc.cycles[0] = cycles;
}
}
return;
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