Sprinter/mame
2
0
Fork 0
mirror of https://github.com/holub/mame synced 2025-07-04 17:38:08 +03:00
Code Issues Actions 36 Packages Projects Releases Wiki Activity

mac128: Principled via sync

Browse Source
This commit is contained in:
Olivier Galibert 2021-03-21 14:32:45 +01:00
parent b772684abb
commit 6c0b2d1642
1 changed files with 27 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
src/mame/drivers/mac128.cpp
View File

@ -193,6 +193,7 @@ private:
void ram_w_se(offs_t offset, uint16_t data, uint16_t mem_mask = ~0);
uint16_t ram_600000_r(offs_t offset);
void ram_600000_w(offs_t offset, uint16_t data, uint16_t mem_mask = ~ 0);
void via_sync();
uint16_t mac_via_r(offs_t offset);
void mac_via_w(offs_t offset, uint16_t data);
uint16_t mac_autovector_r(offs_t offset);
@ -253,7 +254,6 @@ private:
int m_scsi_drq;
// wait states for accessing the VIA
int m_via_cycles;
bool m_snd_enable;
bool m_main_buffer;
int m_snd_vol;
@ -304,7 +304,6 @@ void mac128_state::machine_start()
void mac128_state::machine_reset()
{
m_via_cycles = -10;
m_last_taken_interrupt = -1;
m_overlay = 1;
m_screen_buffer = 1;
@ -680,6 +679,28 @@ WRITE_LINE_MEMBER(mac128_state::mac_via_irq)
set_via_interrupt(state);
}
void mac128_state::via_sync()
{
// The VIA runs from the E clock of the 68k and uses VPA.
// That means:
// - The 68000 starts the access cycle, with AS and the address bus. It's validated at cycle+1.
// - The glue chip sets VPA. The 68000 sees it and acts on it at cycle+2.
// - Between cycle+2 and cycle+11, the E clock goes up. The VIA
// is synced on that clock, so that's at a multiple of 10 in
// absolute time
// - 4 cycles later E goes down and that's the end of the access
uint64_t cur_cycle = m_maincpu->total_cycles();
uint64_t vpa_cycle = cur_cycle+2;
uint64_t via_start_cycle = (vpa_cycle + 9) / 10;
uint64_t end_cycle = via_start_cycle * 10 + 4;
m_maincpu->adjust_icount(cur_cycle - end_cycle);
}
uint16_t mac128_state::mac_via_r(offs_t offset)
{
uint16_t data;
@ -687,9 +708,9 @@ uint16_t mac128_state::mac_via_r(offs_t offset)
offset >>= 8;
offset &= 0x0f;
data = m_via->read(offset);
via_sync();
m_maincpu->adjust_icount(m_via_cycles);
data = m_via->read(offset);
return (data & 0xff) | (data << 8);
}
@ -699,9 +720,9 @@ void mac128_state::mac_via_w(offs_t offset, uint16_t data)
offset >>= 8;
offset &= 0x0f;
m_via->write(offset, (data >> 8) & 0xff);
via_sync();
m_maincpu->adjust_icount(m_via_cycles);
m_via->write(offset, (data >> 8) & 0xff);
}
void mac128_state::mac_autovector_w(offs_t offset, uint16_t data)