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[Core/CD] improved accuracy of CDC DMA processing (verified on real hardware, cf. Krikzz's mcd-verificator)

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This commit is contained in:
ekeeke 2024-01-22 00:22:52 +01:00
parent 16589b558f
commit da8e4e547a
8 changed files with 350 additions and 142 deletions
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3
HISTORY.txt
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@ -24,7 +24,8 @@ Genesis Plus GX 1.7.5 (xx/xx/xxxx) (Eke-Eke)
* improved Timer interrupt timings and CDD interrupt accuracy (fixes audio stutters during Popful Mail FMV)
* improved CDC emulation (fixes random freezes during Jeopardy & ESPN Sunday Night NFL intro)
* improved accuracy of Main-CPU & Sub-CPU access to CDC registers (verified on real hardware, cf. Krikzz's mcd-verificator)
* improved accuracy of CDC transfer to Main-CPU & Sub-CPU (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 emulation of mirrored memory areas
* improved savestate format
* improved Sub-CPU synchronization with Main-CPU (fixes "Soul Star")

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307
core/cd_hw/cdc.c
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@ -62,8 +62,11 @@
/* STAT3 register bitmask */
#define BIT_VALST 0x80
/* TODO: figure exact DMA transfer rate */
#define DMA_BYTES_PER_LINE 512
/* DMA transfer rate */
/* min. 4 x SUB-CPU cycles (i.e 16 x SCD cycles) per byte (cf https://github.com/MiSTer-devel/MegaCD_MiSTer/tree/master/docs/mcd%20logs) */
/* additional delays caused by SUB-CPU access & periodic refresh (all RAM), GPU operation (Word-RAM only) or PCM playback (PCM RAM only) */
/* are not emulated */
#define DMA_CYCLES_PER_BYTE 16
void cdc_init(void)
{
@ -105,11 +108,11 @@ void cdc_reset(void)
cdc.head[1][2] = 0x00;
cdc.head[1][3] = 0x00;
/* reset CDC cycle counter */
/* reset CDC DMA cycle counter */
cdc.cycles = 0;
/* DMA transfer disabled */
cdc.dma_w = 0;
/* disable CDC DMA */
cdc.dma_w = cdc.halted_dma_w = 0;
/* clear any pending IRQ */
if (scd.pending & (1 << 5))
@ -147,12 +150,19 @@ int cdc_context_save(uint8 *state)
{
tmp8 = 5;
}
else if (cdc.halted_dma_w == prg_ram_dma_w)
{
tmp8 = 6;
}
else if (cdc.halted_dma_w == word_ram_2M_dma_w)
{
tmp8 = 7;
}
else
{
tmp8 = 0;
}
save_param(&cdc.ifstat, sizeof(cdc.ifstat));
save_param(&cdc.ifctrl, sizeof(cdc.ifctrl));
save_param(&cdc.dbc, sizeof(cdc.dbc));
@ -194,31 +204,181 @@ int cdc_context_load(uint8 *state)
{
case 1:
cdc.dma_w = pcm_ram_dma_w;
cdc.halted_dma_w = 0;
break;
case 2:
cdc.dma_w = prg_ram_dma_w;
cdc.halted_dma_w = 0;
break;
case 3:
cdc.dma_w = word_ram_0_dma_w;
cdc.halted_dma_w = 0;
break;
case 4:
cdc.dma_w = word_ram_1_dma_w;
cdc.halted_dma_w = 0;
break;
case 5:
cdc.dma_w = word_ram_2M_dma_w;
cdc.halted_dma_w = 0;
break;
case 6:
cdc.dma_w = 0;
cdc.halted_dma_w = prg_ram_dma_w;
break;
case 7:
cdc.dma_w = 0;
cdc.halted_dma_w = word_ram_2M_dma_w;
break;
default:
cdc.dma_w = 0;
cdc.halted_dma_w = 0;
break;
}
return bufferptr;
}
void cdc_dma_update(void)
void cdc_dma_init(void)
{
/* no effect if data transfer is not started */
if (cdc.ifstat & BIT_DTEN)
return;
/* disable DMA by default */
cdc.dma_w = cdc.halted_dma_w = 0;
/* check data transfer destination */
switch (scd.regs[0x04>>1].byte.h & 0x07)
{
case 2: /* MAIN-CPU host read */
case 3: /* SUB-CPU host read */
{
/* read 16-bit word from CDC RAM buffer (big-endian format) into gate-array register $08 */
/* Note: on real-hardware, 16-bit word is not immediately available, cf. https://github.com/MiSTer-devel/MegaCD_MiSTer/blob/master/docs/mcd%20logs/dma_sub_read.jpg for transfer timings */
scd.regs[0x08>>1].w = READ_WORD(cdc.ram, cdc.dac.w & 0x3ffe);
#ifdef LOG_CDC
error("CDC host read 0x%04x -> 0x%04x (dbc=0x%x) (%X)\n", cdc.dac.w, scd.regs[0x08>>1].w, cdc.dbc.w, s68k.pc);
#endif
/* set DSR bit (gate-array register $04) */
scd.regs[0x04>>1].byte.h |= 0x40;
/* increment data address counter */
cdc.dac.w += 2;
/* decrement data byte counter */
cdc.dbc.w -= 2;
/* end of transfer ? */
if ((int16)cdc.dbc.w < 0)
{
/* reset data byte counter (DBCH bits 4-7 should also be set to 1) */
cdc.dbc.w = 0xffff;
/* clear !DTEN and !DTBSY */
cdc.ifstat |= (BIT_DTBSY | BIT_DTEN);
/* pending Data Transfer End interrupt */
cdc.ifstat &= ~BIT_DTEI;
/* Data Transfer End interrupt enabled ? */
if (cdc.ifctrl & BIT_DTEIEN)
{
/* pending level 5 interrupt */
scd.pending |= (1 << 5);
/* level 5 interrupt enabled ? */
if (scd.regs[0x32>>1].byte.l & 0x20)
{
/* update IRQ level */
s68k_update_irq((scd.pending & scd.regs[0x32>>1].byte.l) >> 1);
}
}
/* set EDT bit (gate-array register $04) */
scd.regs[0x04>>1].byte.h |= 0x80;
}
break;
}
case 4: /* PCM RAM DMA */
{
cdc.dma_w = pcm_ram_dma_w;
break;
}
case 5: /* PRG-RAM DMA */
{
/* check if MAIN-CPU has access to PRG-RAM */
if (scd.regs[0x00].byte.l & 0x02)
{
/* halt DMA to PRG-RAM */
cdc.halted_dma_w = prg_ram_dma_w;
}
else
{
/* enable DMA to PRG-RAM */
cdc.dma_w = prg_ram_dma_w;
}
break;
}
case 7: /* Word-RAM DMA */
{
/* check memory mode */
if (scd.regs[0x02 >> 1].byte.l & 0x04)
{
/* 1M mode */
if (scd.regs[0x02 >> 1].byte.l & 0x01)
{
/* Word-RAM bank 0 is assigned to SUB-CPU */
cdc.dma_w = word_ram_0_dma_w;
}
else
{
/* Word-RAM bank 1 is assigned to SUB-CPU */
cdc.dma_w = word_ram_1_dma_w;
}
}
else
{
/* check if MAIN-CPU has access to 2M Word-RAM */
if (scd.regs[0x02 >> 1].byte.l & 0x01)
{
/* halt DMA to 2M Word-RAM */
cdc.halted_dma_w = word_ram_2M_dma_w;
}
else
{
/* enable DMA to 2M Word-RAM */
cdc.dma_w = word_ram_2M_dma_w;
}
}
break;
}
default: /* invalid */
{
#ifdef LOG_CDC
error("invalid CDC transfer destination (%d)\n", scd.regs[0x04>>1].byte.h & 0x07);
#endif
break;
}
}
}
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;
/* always process blocks of 8 bytes */
dma_bytes = (dma_bytes / 8) * 8;
/* end of DMA transfer ? */
if (cdc.dbc.w < DMA_BYTES_PER_LINE)
if (cdc.dbc.w < dma_bytes)
{
/* transfer remaining bytes using DMA */
cdc.dma_w(cdc.dbc.w + 1);
@ -252,8 +412,8 @@ void cdc_dma_update(void)
/* SUB-CPU idle on register $04 polling ? */
if (s68k.stopped & (1<<0x04))
{
/* sync SUB-CPU with CDC */
s68k.cycles = scd.cycles;
/* sync SUB-CPU with CDC DMA */
s68k.cycles = cdc.cycles;
/* restart SUB-CPU */
s68k.stopped = 0;
@ -262,16 +422,19 @@ void cdc_dma_update(void)
#endif
}
/* disable DMA transfer */
cdc.dma_w = 0;
/* disable DMA */
cdc.dma_w = cdc.halted_dma_w = 0;
}
else
else if (dma_bytes > 0)
{
/* transfer limited amount of bytes using DMA */
cdc.dma_w(DMA_BYTES_PER_LINE);
cdc.dma_w(dma_bytes);
/* decrement data byte counter */
cdc.dbc.w -= DMA_BYTES_PER_LINE;
cdc.dbc.w -= dma_bytes;
/* update DMA cycle counter */
cdc.cycles += dma_bytes * DMA_CYCLES_PER_BYTE;
}
}
@ -403,6 +566,9 @@ void cdc_reg_w(unsigned char data)
{
/* clear !DTBSY and !DTEN */
cdc.ifstat |= (BIT_DTBSY | BIT_DTEN);
/* disable DMA */
cdc.dma_w = cdc.halted_dma_w = 0;
}
cdc.ifctrl = data;
@ -436,110 +602,11 @@ void cdc_reg_w(unsigned char data)
/* clear EDT & DSR bits (gate-array register $04) */
scd.regs[0x04>>1].byte.h &= 0x07;
/* setup data transfer destination */
switch (scd.regs[0x04>>1].byte.h & 0x07)
{
case 2: /* MAIN-CPU host read */
case 3: /* SUB-CPU host read */
{
/* read 16-bit word from CDC RAM buffer (big-endian format) into gate-array register $08 */
/* Note: on real-hardware, 16-bit word is not immediately available, cf. https://github.com/MiSTer-devel/MegaCD_MiSTer/blob/master/docs/mcd%20logs/dma_sub_read.jpg for transfer timings */
scd.regs[0x08>>1].w = READ_WORD(cdc.ram, cdc.dac.w & 0x3ffe);
#ifdef LOG_CDC
error("CDC host read 0x%04x -> 0x%04x (dbc=0x%x) (%X)\n", cdc.dac.w, scd.regs[0x08>>1].w, cdc.dbc.w, s68k.pc);
#endif
/* initialize data transfer destination */
cdc_dma_init();
/* set DSR bit (gate-array register $04) */
scd.regs[0x04>>1].byte.h |= 0x40;
/* increment data address counter */
cdc.dac.w += 2;
/* decrement data byte counter */
cdc.dbc.w -= 2;
/* end of transfer ? */
if ((int16)cdc.dbc.w < 0)
{
/* reset data byte counter (DBCH bits 4-7 should also be set to 1) */
cdc.dbc.w = 0xffff;
/* clear !DTEN and !DTBSY */
cdc.ifstat |= (BIT_DTBSY | BIT_DTEN);
/* pending Data Transfer End interrupt */
cdc.ifstat &= ~BIT_DTEI;
/* Data Transfer End interrupt enabled ? */
if (cdc.ifctrl & BIT_DTEIEN)
{
/* pending level 5 interrupt */
scd.pending |= (1 << 5);
/* level 5 interrupt enabled ? */
if (scd.regs[0x32>>1].byte.l & 0x20)
{
/* update IRQ level */
s68k_update_irq((scd.pending & scd.regs[0x32>>1].byte.l) >> 1);
}
}
/* set EDT bit (gate-array register $04) */
scd.regs[0x04>>1].byte.h |= 0x80;
}
break;
}
case 4: /* PCM RAM DMA */
{
cdc.dma_w = pcm_ram_dma_w;
break;
}
case 5: /* PRG-RAM DMA */
{
cdc.dma_w = prg_ram_dma_w;
break;
}
case 7: /* WORD-RAM DMA */
{
/* check memory mode */
if (scd.regs[0x02 >> 1].byte.l & 0x04)
{
/* 1M mode */
if (scd.regs[0x02 >> 1].byte.l & 0x01)
{
/* Word-RAM bank 0 is assigned to SUB-CPU */
cdc.dma_w = word_ram_0_dma_w;
}
else
{
/* Word-RAM bank 1 is assigned to SUB-CPU */
cdc.dma_w = word_ram_1_dma_w;
}
}
else
{
/* 2M mode */
if (scd.regs[0x02 >> 1].byte.l & 0x02)
{
/* only process DMA if Word-RAM is assigned to SUB-CPU */
cdc.dma_w = word_ram_2M_dma_w;
}
}
break;
}
default: /* invalid */
{
#ifdef LOG_CDC
error("invalid CDC transfer destination (%d)\n", scd.regs[0x04>>1].byte.h & 0x07);
#endif
break;
}
}
/* initialize DMA cycle counter */
cdc.cycles = s68k.cycles;
}
break;
@ -623,7 +690,7 @@ void cdc_reg_w(unsigned char data)
cdc_reset();
break;
default: /* unemulated registers*/
default: /* unemulated registers */
break;
}
@ -757,7 +824,7 @@ unsigned char cdc_reg_r(void)
}
#ifdef LOG_CDC
error("CDC register %d read 0x%02X (%X)\n", scd.regs[0x04>>1].byte.l, data, s68k.pc);
error("CDC register %d read 0x%02X (%X)\n", scd.regs[0x04>>1].byte.l, data, s68k.pc);
#endif
/* increment address register (except when register #0 is selected) */

8
core/cd_hw/cdc.h
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@ -55,8 +55,9 @@ typedef struct
uint8 ctrl[2];
uint8 head[2][4];
uint8 stat[4];
int cycles;
void (*dma_w)(unsigned int length); /* DMA transfer callback */
unsigned int cycles;
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) */
uint8 ar_mask;
} cdc_t;
@ -66,7 +67,8 @@ extern void cdc_init(void);
extern void cdc_reset(void);
extern int cdc_context_save(uint8 *state);
extern int cdc_context_load(uint8 *state);
extern void cdc_dma_update(void);
extern void cdc_dma_init(void);
extern void cdc_dma_update(unsigned int cycles);
extern void cdc_decoder_update(uint32 header);
extern void cdc_reg_w(unsigned char data);
extern unsigned char cdc_reg_r(void);

71
core/cd_hw/scd.c
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@ -1003,6 +1003,17 @@ static void scd_write_byte(unsigned int address, unsigned int data)
gfx_update(s68k.cycles);
}
/* check if CDC DMA to 2M Word-RAM is running */
if (cdc.dma_w == word_ram_2M_dma_w)
{
/* synchronize CDC DMA with SUB-CPU */
cdc_dma_update(s68k.cycles);
/* halt CDC DMA to 2M Word-RAM */
cdc.dma_w = 0;
cdc.halted_dma_w = word_ram_2M_dma_w;
}
/* Word-RAM is returned to MAIN-CPU */
scd.dmna = 0;
@ -1038,6 +1049,24 @@ static void scd_write_byte(unsigned int address, unsigned int data)
return;
}
case 0x04: /* CDC mode */
{
scd.regs[0x04 >> 1].byte.h = data & 0x07;
/* synchronize CDC DMA (if running) with SUB-CPU */
if (cdc.dma_w)
{
cdc_dma_update(s68k.cycles);
}
/* reinitialize CDC data transfer destination (verified on real hardware, cf. Krikzz's mcd-verificator) */
cdc_dma_init();
/* reset CDC DMA address (verified on real hardware, cf. Krikzz's mcd-verificator) */
scd.regs[0x0a >> 1].w = 0;
return;
}
case 0x05: /* CDC register address */
{
scd.regs[0x04 >> 1].byte.l = data & cdc.ar_mask;
@ -1312,6 +1341,17 @@ static void scd_write_word(unsigned int address, unsigned int data)
gfx_update(s68k.cycles);
}
/* check if CDC DMA to 2M Word-RAM is running */
if (cdc.dma_w == word_ram_2M_dma_w)
{
/* synchronize CDC DMA with SUB-CPU */
cdc_dma_update(s68k.cycles);
/* halt CDC DMA to 2M Word-RAM */
cdc.dma_w = 0;
cdc.halted_dma_w = word_ram_2M_dma_w;
}
/* Word-RAM is returned to MAIN-CPU */
scd.dmna = 0;
@ -1350,6 +1390,18 @@ static void scd_write_word(unsigned int address, unsigned int data)
case 0x04: /* CDC mode & register address */
{
scd.regs[0x04 >> 1].w = data & (0x0700 | cdc.ar_mask);
/* synchronize CDC DMA (if running) with SUB-CPU */
if (cdc.dma_w)
{
cdc_dma_update(s68k.cycles);
}
/* reinitialize CDC data transfer destination (verified on real hardware, cf. Krikzz's mcd-verificator) */
cdc_dma_init();
/* reset CDC DMA address (verified on real hardware, cf. Krikzz's mcd-verificator) */
scd.regs[0x0a >> 1].w = 0;
return;
}
@ -1833,16 +1885,6 @@ void scd_update(unsigned int cycles)
int s68k_run_cycles;
int s68k_end_cycles = scd.cycles + SCYCLES_PER_LINE;
/* update CDC DMA transfer */
if (cdc.dma_w)
{
/* check if Word-RAM is returned to SUB-CPU in 2M mode */
if ((cdc.dma_w != word_ram_2M_dma_w) || scd.dmna)
{
cdc_dma_update();
}
}
/* run both CPU in sync until end of line */
do
{
@ -1918,10 +1960,15 @@ void scd_update(unsigned int cycles)
}
while ((m68k.cycles < cycles) || (s68k.cycles < s68k_end_cycles));
/* GFX processing */
/* update CDC DMA processing (if running) */
if (cdc.dma_w)
{
cdc_dma_update(scd.cycles);
}
/* update GFX processing (if started) */
if (scd.regs[0x58>>1].byte.h & 0x80)
{
/* update graphics operation if running */
gfx_update(scd.cycles);
}
}

103
core/mem68k.c
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@ -756,6 +756,17 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
m68k.memory_map[base].write16 = m68k.memory_map[base+1].write16 = NULL;
zbank_memory_map[base].read = zbank_memory_map[base+1].read = NULL;
zbank_memory_map[base].write = zbank_memory_map[base+1].write = NULL;
/* check if CDC DMA to PRG-RAM is running */
if (cdc.dma_w == prg_ram_dma_w)
{
/* synchronize CDC DMA with MAIN-CPU */
cdc_dma_update((m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE);
/* halt CDC DMA to PRG-RAM */
cdc.dma_w = 0;
cdc.halted_dma_w = prg_ram_dma_w;
}
}
else
{
@ -765,6 +776,23 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
m68k.memory_map[base].write16 = m68k.memory_map[base+1].write16 = m68k_unused_16_w;
zbank_memory_map[base].read = zbank_memory_map[base+1].read = zbank_unused_r;
zbank_memory_map[base].write = zbank_memory_map[base+1].write = zbank_unused_w;
/* check if CDC DMA to PRG-RAM is halted */
if (cdc.halted_dma_w == prg_ram_dma_w)
{
/* relative SUB-CPU cycle counter */
unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
/* enable CDC DMA to PRG-RAM */
cdc.dma_w = prg_ram_dma_w;
cdc.halted_dma_w = 0;
/* synchronize CDC DMA with MAIN-CPU (only if not already ahead) */
if (cdc.cycles < cycles)
{
cdc.cycles = cycles;
}
}
}
}
@ -840,7 +868,7 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
/* check if SUB-CPU is waiting for Word-RAM access */
if (s68k.stopped & 0x04)
{
/* sync SUB-CPU with MAIN-CPU */
/* synchronize SUB-CPU with MAIN-CPU */
s68k.cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
/* restart SUB-CPU */
@ -850,18 +878,36 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
#endif
}
/* check if graphics operation is running */
/* check if graphics operation is started */
if (scd.regs[0x58>>1].byte.h & 0x80)
{
/* relative SUB-CPU cycle counter */
unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
/* synchronize GFX processing with SUB-CPU (only if not already ahead) */
/* synchronize GFX processing with MAIN-CPU (only if not already ahead) */
if (gfx.cycles < cycles)
{
gfx.cycles = cycles;
}
}
/* check if CDC DMA to 2M Word-RAM is halted */
if (cdc.halted_dma_w == word_ram_2M_dma_w)
{
/* relative SUB-CPU cycle counter */
unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
/* enable CDC DMA to 2M Word-RAM */
cdc.dma_w = word_ram_2M_dma_w;
cdc.halted_dma_w = 0;
/* synchronize CDC DMA with MAIN-CPU (only if not already ahead) */
if (cdc.cycles < cycles)
{
cdc.cycles = cycles;
}
}
return;
}
}
@ -1039,6 +1085,17 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
m68k.memory_map[base].write16 = m68k.memory_map[base+1].write16 = NULL;
zbank_memory_map[base].read = zbank_memory_map[base+1].read = NULL;
zbank_memory_map[base].write = zbank_memory_map[base+1].write = NULL;
/* check if CDC DMA to PRG-RAM is running */
if (cdc.dma_w == prg_ram_dma_w)
{
/* synchronize CDC DMA with MAIN-CPU */
cdc_dma_update((m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE);
/* halt CDC DMA to PRG-RAM */
cdc.dma_w = 0;
cdc.halted_dma_w = prg_ram_dma_w;
}
}
else
{
@ -1048,6 +1105,23 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
m68k.memory_map[base].write16 = m68k.memory_map[base+1].write16 = m68k_unused_16_w;
zbank_memory_map[base].read = zbank_memory_map[base+1].read = zbank_unused_r;
zbank_memory_map[base].write = zbank_memory_map[base+1].write = zbank_unused_w;
/* check if CDC DMA to PRG-RAM is halted */
if (cdc.halted_dma_w == prg_ram_dma_w)
{
/* relative SUB-CPU cycle counter */
unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
/* enable CDC DMA to PRG-RAM */
cdc.dma_w = prg_ram_dma_w;
cdc.halted_dma_w = 0;
/* synchronize CDC DMA with MAIN-CPU (only if not already ahead) */
if (cdc.cycles < cycles)
{
cdc.cycles = cycles;
}
}
}
}
@ -1133,7 +1207,7 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
/* check if SUB-CPU is waiting for Word-RAM access */
if (s68k.stopped & 0x04)
{
/* sync SUB-CPU with MAIN-CPU */
/* synchronize SUB-CPU with MAIN-CPU */
s68k.cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
/* restart SUB-CPU */
@ -1143,18 +1217,35 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
#endif
}
/* check if graphics operation is running */
/* check if graphics operation is started */
if (scd.regs[0x58>>1].byte.h & 0x80)
{
/* relative SUB-CPU cycle counter */
unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
/* synchronize GFX processing with SUB-CPU (only if not already ahead) */
/* synchronize GFX processing with MAIN-CPU (only if not already ahead) */
if (gfx.cycles < cycles)
{
gfx.cycles = cycles;
}
}
/* check if CDC DMA to 2M Word-RAM is halted */
if (cdc.halted_dma_w == word_ram_2M_dma_w)
{
/* relative SUB-CPU cycle counter */
unsigned int cycles = (m68k.cycles * SCYCLES_PER_LINE) / MCYCLES_PER_LINE;
/* enable CDC DMA to 2M Word-RAM */
cdc.dma_w = word_ram_2M_dma_w;
cdc.halted_dma_w = 0;
/* synchronize CDC DMA with MAIN-CPU (only if not already ahead) */
if (cdc.cycles < cycles)
{
cdc.cycles = cycles;
}
}
return;
}
}