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macqd700: Throttle CPU when doing SCSI pseudo-DMA to make 53C96 clock and transfer rates more realistic

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This commit is contained in:
AJR 2023-03-03 07:49:09 -05:00
parent 78aadc3ef2
commit 1c9ce36b23
1 changed files with 24 additions and 5 deletions
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29
src/mame/apple/macquadra700.cpp
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@ -196,6 +196,8 @@ private:
uint8_t mac_5396_r(offs_t offset);
void mac_5396_w(offs_t offset, uint8_t data);
uint16_t mac_5396_dma_r(offs_t offset);
void mac_5396_dma_w(offs_t offset, uint16_t data);
};
void macquadra_state::field_interrupts()
@ -776,6 +778,26 @@ void macquadra_state::mac_5396_w(offs_t offset, uint8_t data)
m_ncr1->write(offset>>4, data);
}
uint16_t macquadra_state::mac_5396_dma_r(offs_t offset)
{
// HACK: Extra time is necessary to avoid underrunning the FIFO at 4 MB/sec transfer rates claimed to
// be typical for Apple HDDs of the period.
// Likely due to inaccurate 68040 bus timings or wait states; DAFB documentation is clear that there is
// no "magic latch" like the 5380 machines use.
if (!machine().side_effects_disabled() && BIT(offset << 1, 18))
m_maincpu->adjust_icount(-4);
return m_ncr1->dma16_swap_r();
}
void macquadra_state::mac_5396_dma_w(offs_t offset, uint16_t data)
{
if (!machine().side_effects_disabled() && BIT(offset << 1, 18))
m_maincpu->adjust_icount(-4);
m_ncr1->dma16_swap_w(data);
}
/***************************************************************************
ADDRESS MAPS
***************************************************************************/
@ -789,7 +811,7 @@ void macquadra_state::quadra700_map(address_map &map)
// 5000a000 = Sonic (DP83932) ethernet
// 5000f000 = SCSI cf96, 5000f402 = SCSI #2 cf96
map(0x5000f000, 0x5000f0ff).rw(FUNC(macquadra_state::mac_5396_r), FUNC(macquadra_state::mac_5396_w)).mirror(0x00fc0000);
map(0x5000f100, 0x5000f101).rw(m_ncr1, FUNC(ncr53c94_device::dma16_swap_r), FUNC(ncr53c94_device::dma16_swap_w)).mirror(0x00fc0000);
map(0x5000f100, 0x5000f101).rw(FUNC(macquadra_state::mac_5396_dma_r), FUNC(macquadra_state::mac_5396_dma_w)).select(0x00fc0000);
map(0x5000c000, 0x5000dfff).rw(FUNC(macquadra_state::mac_scc_r), FUNC(macquadra_state::mac_scc_2_w)).mirror(0x00fc0000);
map(0x50014000, 0x50015fff).rw(m_easc, FUNC(asc_device::read), FUNC(asc_device::write)).mirror(0x00fc0000);
map(0x5001e000, 0x5001ffff).rw(FUNC(macquadra_state::swim_r), FUNC(macquadra_state::swim_w)).mirror(0x00fc0000);
@ -931,10 +953,7 @@ void macquadra_state::macqd700(machine_config &config)
NSCSI_CONNECTOR(config, "scsi1:4", mac_scsi_devices, "cdrom");
NSCSI_CONNECTOR(config, "scsi1:5", mac_scsi_devices, nullptr);
NSCSI_CONNECTOR(config, "scsi1:6", mac_scsi_devices, "harddisk");
// HACK: Max clock for 5394/96 is 25 MHz, but we underrun the FIFO at that speed.
// Likely due to inaccurate 68040 and/or NSCSI bus timings; DAFB documentation is clear that there is
// no "magic latch" like the 5380 machines use.
NSCSI_CONNECTOR(config, "scsi1:7").option_set("ncr53c96", NCR53C96).clock(50_MHz_XTAL).machine_config(
NSCSI_CONNECTOR(config, "scsi1:7").option_set("ncr53c96", NCR53C96).clock(50_MHz_XTAL / 2).machine_config(
[this] (device_t *device)
{
ncr53c96_device &adapter = downcast<ncr53c96_device &>(*device);