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apple/apple3_m.cpp: Reduce CPU clock frequency during active video display. (#11505)

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Also adjusted fast CPU clock frequency to approximate the effects of DRAM refresh and other delays.
This commit is contained in:
robjustice 2023-08-29 06:42:13 +10:00 committed by GitHub
parent ffe788280c
commit a482aacc56
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 26 additions and 8 deletions
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34
src/mame/apple/apple3_m.cpp
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@ -63,9 +63,15 @@
#define ENV_ROMENABLE (0x01)
// 14M / 14, but with every 65th cycle stretched which we cannot reasonably emulate
// 2 MHz mode probably has every 33rd cycle stretched but this is currently unproven.
static constexpr XTAL APPLE2_CLOCK(1'021'800);
// 2 MHz mode has every ~130th cycle stretched, and there are also dram refresh cycles
// happening which slows the clock back to 1MHz for some periods.
// There is mentioned in Apple documentation the result is ~1.8MHz
// PH0 Measured on a logic analyser when running a loop in ram with the screen off
// averaged over a long capture is 1.905MHz.
static constexpr XTAL A3_2MHZ_CLOCK(1'905'000);
uint8_t apple3_state::apple3_c0xx_r(offs_t offset)
{
uint8_t result = 0xFF;
@ -532,7 +538,7 @@ void apple3_state::apple3_update_memory()
LOGMASKED(LOG_MEMORY, "apple3_update_memory(): via_0_b=0x%02x via_1_a=0x0x%02x\n", m_via_0_b, m_via_1_a);
m_maincpu->set_unscaled_clock(((m_via_0_a & ENV_SLOWSPEED) ? APPLE2_CLOCK : (14.318181_MHz_XTAL / 7)), true);
m_maincpu->set_unscaled_clock(((m_via_0_a & ENV_SLOWSPEED) ? APPLE2_CLOCK : A3_2MHZ_CLOCK), true);
/* bank 2 (0100-01FF) */
if (!(m_via_0_a & ENV_STACK1XX))
@ -1109,11 +1115,17 @@ TIMER_CALLBACK_MEMBER(apple3_state::scanstart_cb)
int scanline;
scanline = m_screen->vpos();
//m_screen->update_partial(m_screen->vpos());
m_screen->update_partial(m_screen->vpos());
m_via[1]->write_pb6(0);
m_scanend->adjust(m_screen->time_until_pos(scanline, 559));
// Drop back to 1Mhz for video memory access
if (!(m_via_0_a & ENV_SLOWSPEED) && (m_via_0_a & ENV_VIDENABLE))
{
m_maincpu->set_unscaled_clock(APPLE2_CLOCK, true);
}
}
TIMER_CALLBACK_MEMBER(apple3_state::scanend_cb)
@ -1122,7 +1134,13 @@ TIMER_CALLBACK_MEMBER(apple3_state::scanend_cb)
m_via[1]->write_pb6(1);
m_scanstart->adjust(m_screen->time_until_pos((scanline+1) % 224, 0));
m_scanstart->adjust(m_screen->time_until_pos((scanline+1) % 192, 0));
// And back to 2MHz during blanking
if (!(m_via_0_a & ENV_SLOWSPEED) && (m_via_0_a & ENV_VIDENABLE))
{
m_maincpu->set_unscaled_clock(A3_2MHZ_CLOCK, true);
}
}
INPUT_CHANGED_MEMBER(apple3_state::keyb_special_changed)
@ -1354,7 +1372,7 @@ void apple3_state::pdl_handler(int offset)
case 0x5c:
m_ramp_active = false;
m_pdl_charge = 0;
m_pdltimer->adjust(attotime::from_hz(1000000.0));
m_pdltimer->adjust(attotime::from_hz(950000.0));
break;
case 0x5d:
@ -1387,7 +1405,7 @@ void apple3_state::pdl_handler(int offset)
m_pdl_charge += (pdlread*7);
m_pdl_charge -= 100;
}
m_pdltimer->adjust(attotime::from_hz(1000000.0));
m_pdltimer->adjust(attotime::from_hz(950000.0));
m_ramp_active = true;
break;
@ -1409,7 +1427,7 @@ TIMER_DEVICE_CALLBACK_MEMBER(apple3_state::paddle_timer)
if (m_pdl_charge > 0)
{
m_pdltimer->adjust(attotime::from_hz(1000000.0));
m_pdltimer->adjust(attotime::from_hz(950000.0));
}
else
{
@ -1420,7 +1438,7 @@ TIMER_DEVICE_CALLBACK_MEMBER(apple3_state::paddle_timer)
else
{
m_pdl_charge++;
m_pdltimer->adjust(attotime::from_hz(1000000.0));
m_pdltimer->adjust(attotime::from_hz(950000.0));
}
}