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labtam: improved interrupt map logic

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This commit is contained in:
Patrick Mackinlay 2022-06-16 15:01:49 +07:00
parent e7fe75fd5c
commit 184259c82d
2 changed files with 30 additions and 32 deletions
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59
src/devices/bus/multibus/labtam_z80sbc.cpp
View File

@ -62,7 +62,8 @@ enum drvstatus_mask : u8
DRVSTATUS_G = 0x08, // FD3 is mini floppy
DRVSTATUS_B = 0x10, // not used
DRVSTATUS_D = 0x20, // not used
DRVSTATUS_SS = 0x40, // 8" floppy is single-sided
DRVSTATUS_F = 0x40, // ?
DRVSTATUS_DS = 0x80, // floppy is double-sided
};
DEFINE_DEVICE_TYPE(LABTAM_Z80SBC, labtam_z80sbc_device, "labtam_z80sbc", "Labtam Z80 SBC")
@ -240,6 +241,7 @@ void labtam_z80sbc_device::device_start()
save_item(NAME(m_map_mux));
save_item(NAME(m_map_num));
save_item(NAME(m_map_cnt));
}
void labtam_z80sbc_device::device_reset()
@ -264,6 +266,7 @@ void labtam_z80sbc_device::device_reset()
m_map_mux = 0;
m_map_num = 0;
m_map_cnt = 0;
m_fdcstatus = 0x3c;
m_dma[0]->iei_w(1);
@ -283,7 +286,6 @@ void labtam_z80sbc_device::device_add_mconfig(machine_config &config)
{
Z80(config, m_cpu, 20_MHz_XTAL / 4);
m_cpu->set_addrmap(AS_PROGRAM, &labtam_z80sbc_device::cpu_mem);
m_cpu->set_addrmap(AS_OPCODES, &labtam_z80sbc_device::cpu_mem);
m_cpu->set_addrmap(AS_IO, &labtam_z80sbc_device::cpu_pio);
m_cpu->irqack_cb().set([this](int state) { m_map_mux |= MM_PND; });
m_cpu->set_daisy_config(daisy_chain);
@ -389,13 +391,18 @@ void labtam_z80sbc_device::cpu_pio(address_map &map)
map(0x00e0, 0x00ff).mirror(0xff00).rw(m_rtc, FUNC(mm58167_device::read), FUNC(mm58167_device::write));
}
u8 labtam_z80sbc_device::mem_r(address_space &space, offs_t offset)
u8 labtam_z80sbc_device::mem_r(offs_t offset)
{
// check for and complete pending map number change
if ((m_map_mux & MM_PND) && (space.spacenum() == AS_PROGRAM) && !machine().side_effects_disabled())
if ((m_map_mux & MM_PND) && !machine().side_effects_disabled())
{
m_map_mux &= ~MM_PND;
m_map_mux ^= MM_INT;
if (m_map_cnt == 0)
{
m_map_mux &= ~MM_PND;
m_map_mux ^= MM_INT;
}
else
m_map_cnt--;
}
if (m_map_mux & MM_ENB)
@ -485,27 +492,17 @@ void labtam_z80sbc_device::map_w(unsigned map_num, offs_t offset, u8 data)
void labtam_z80sbc_device::intswt_w(u8 data)
{
/*
* Writing to this port toggles between interrupt (map number forced to 0) and
* user (map number from mapnum latch) mode. The mapping mode can be applied
* immediately, or only upon the next non-instruction memory read. The delay
* mechanism is used to support interrupts:
*
* - When an interrupt is taken, the delayed map change allows the Z80 to
* store the return address on the currently mapped stack, before switching
* to map 0 to fetch the interrupt vector address.
*
* - When returning from an interrupt handler, the delayed map change allows
* further instructions (including RET) to be fetched from the interrupt
* service routine using map 0, while the return address will be fetched
* from the user mapped stack.
* Writing to this port deactivates the interrupt map after the next three
* Z80 memory read cycles. This delay supports interrupt return, allowing
* the standard epilogue of NOP, EI, and RET to be fetched and executed
* from map 0, before the return address is fetched from the non-interrupt
* memory map.
*/
LOG("intswt_w 0x%02x mapnum 0x%02x (%s)\n", data, m_map_num, machine().describe_context());
LOG("intswt map 0x%02x mux 0x%02x (%s)\n", m_map_num, m_map_mux, machine().describe_context());
if (BIT(data, 0))
m_map_mux ^= MM_INT;
else
m_map_mux |= MM_PND;
m_map_mux |= MM_PND;
m_map_cnt = 3;
}
void labtam_z80sbc_device::mapnum_w(u8 data)
@ -515,7 +512,7 @@ void labtam_z80sbc_device::mapnum_w(u8 data)
m_map_mux |= MM_ENB;
// TODO: what are bits 3, 4 and 5 used for?
m_map_num = data & 0x3f;
m_map_num = data & 0x07;
}
void labtam_z80sbc_device::fdcint_w(int state)
@ -596,12 +593,12 @@ u8 labtam_z80sbc_device::drvstatus_r()
{
u8 data = m_e21->read();
// TODO: read selected floppy twosid_r()
#if 0
floppy_image_device *fid = m_fdd[*m_drive]->get_device();
if (fid && !fid->twosid_r())
data |= DRVSTATUS_SS;
#endif
if (m_drive)
{
floppy_image_device *fid = m_fdd[*m_drive]->get_device();
if (fid && !fid->twosid_r())
data |= DRVSTATUS_DS;
}
return data;
}

3
src/devices/bus/multibus/labtam_z80sbc.h
View File

@ -41,7 +41,7 @@ private:
void cpu_pio(address_map &map);
// cpu memory handlers
u8 mem_r(address_space &space, offs_t offset);
u8 mem_r(offs_t offset);
void mem_w(offs_t offset, u8 data);
// memory mapping handlers
@ -85,6 +85,7 @@ private:
u8 m_map_mux;
u8 m_map_num;
u8 m_map_cnt;
u8 m_fdcstatus;
std::optional<u8> m_drive;