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md, implement z80 cycle stealing when accessing 68k bus

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this fixes sound issues in Overdrive 2
This commit is contained in:
kub 2023-04-05 20:02:47 +02:00
parent d515a352b3
commit 134092feb7
3 changed files with 37 additions and 7 deletions
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30
pico/pico_cmn.c
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@ -41,11 +41,22 @@ static void SekExecM68k(int cyc_do)
static void SekSyncM68k(void)
{
int cyc_do;
pprof_start(m68k);
pevt_log_m68k_o(EVT_RUN_START);
while ((cyc_do = Pico.t.m68c_aim - Pico.t.m68c_cnt) > 0)
SekExecM68k(cyc_do);
while ((cyc_do = Pico.t.m68c_aim - Pico.t.m68c_cnt) > 0) {
// the Z80 CPU is stealing some bus cycles from the 68K main CPU when
// accessing the 68K RAM or ROM. Account for these by shortening the time
// the 68K CPU runs.
int z80_buscyc = Pico.t.z80_buscycles;
if (z80_buscyc <= cyc_do)
SekExecM68k(cyc_do - z80_buscyc);
else
z80_buscyc = cyc_do;
Pico.t.m68c_cnt += z80_buscyc;
Pico.t.z80_buscycles -= z80_buscyc;
}
SekTrace(0);
pevt_log_m68k_o(EVT_RUN_END);
@ -56,9 +67,7 @@ static __inline void SekRunM68k(int cyc)
{
Pico.t.m68c_aim += cyc;
Pico.t.m68c_cnt += cyc >> 6; // refresh slowdowns
cyc = Pico.t.m68c_aim - Pico.t.m68c_cnt;
if (cyc <= 0)
return;
SekSyncM68k();
}
@ -90,11 +99,20 @@ static void do_hint(struct PicoVideo *pv)
static void do_timing_hacks_end(struct PicoVideo *pv)
{
PicoVideoFIFOSync(CYCLES_M68K_LINE);
// need rather tight Z80 sync for emulation of main bus cycle stealing
if (Pico.m.z80Run && !Pico.m.z80_reset && (PicoIn.opt&POPT_EN_Z80) && (Pico.m.scanline&1))
PicoSyncZ80(Pico.t.m68c_aim);
}
static void do_timing_hacks_start(struct PicoVideo *pv)
{
SekCyclesBurn(PicoVideoFIFOHint()); // prolong cpu HOLD if necessary
int cycles = PicoVideoFIFOHint();
SekCyclesBurn(cycles); // prolong cpu HOLD if necessary
// XXX how to handle Z80 bus cycle stealing during DMA correctly?
if ((Pico.t.z80_buscycles -= cycles) < 0)
Pico.t.z80_buscycles = 0;
}
static int PicoFrameHints(void)