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amstrad: workaround to make PPI port C ignore I/O status on Plus systems. Fixes system detection on Allergy demo.

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This commit is contained in:
mahlemiut 2015-11-30 11:41:52 +13:00
parent 36ce16ddb0
commit 2f470cfbba
2 changed files with 12 additions and 4 deletions
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1
src/mame/includes/amstrad.h
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@ -317,6 +317,7 @@ protected:
virtual void device_timer(emu_timer &timer, device_timer_id id, int param, void *ptr);
int m_centronics_busy;
UINT8 m_last_write;
};

15
src/mame/machine/amstrad.cpp
View File

@ -1863,8 +1863,8 @@ READ8_MEMBER(amstrad_state::amstrad_cpc_io_r)
}
}
if ( m_system_type == SYSTEM_PLUS || m_system_type == SYSTEM_GX4000 ) // Plus systems return 0 when attempting to read the gate array (and any other unreadable space too?)
data = 0;
if ( m_system_type == SYSTEM_PLUS || m_system_type == SYSTEM_GX4000 ) // Plus systems return 0x78 (464+) or 0x79 (6128+) when attempting to read the gate array (and any other unreadable space too?)
data = 0x79;
/* if b14 = 0 : CRTC Read selected */
if ((offset & (1<<14)) == 0)
@ -1913,6 +1913,9 @@ b9 b8 | PPI Function Read/Write status
{
if (r1r0 < 0x03 )
data = m_ppi->read(space, r1r0);
if ( m_system_type == SYSTEM_PLUS || m_system_type == SYSTEM_GX4000 ) // Plus systems return the data written to port C (I/O status is ignored)
if(r1r0 == 0x02)
data = m_last_write;
}
/* if b10 = 0 : Expansion Peripherals Read selected
@ -2104,9 +2107,11 @@ WRITE8_MEMBER(amstrad_state::amstrad_cpc_io_w)
*/
if ((offset & (1<<11)) == 0)
{
unsigned int Index = ((offset & 0x0300) >> 8);
unsigned int idx = ((offset & 0x0300) >> 8);
m_ppi->write(space, Index, data);
m_ppi->write(space, idx, data);
if(idx == 0x02)
m_last_write = data;
}
/* if b10 = 0 : Expansion Peripherals Write selected */
@ -2335,6 +2340,8 @@ Once all tables and jumpblocks have been set up,
control is passed to the default entry in rom 0*/
void amstrad_state::amstrad_reset_machine()
{
m_last_write = 0xff;
/* enable lower rom (OS rom) */
amstrad_GateArray_write(0x089);