home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
AmigActive 10
/
AACD 10.iso
/
AACD
/
Games
/
MAME
/
src
/
sndhrdw
/
frogger.c
< prev
next >
Wrap
C/C++ Source or Header
|
2000-04-04
|
2KB
|
73 lines
#include "driver.h"
/* The timer clock which feeds the upper 4 bits of */
/* AY-3-8910 port A is based on the same clock */
/* feeding the sound CPU Z80. It is a divide by */
/* 5120, formed by a standard divide by 512, */
/* followed by a divide by 10 using a 4 bit */
/* bi-quinary count sequence. (See LS90 data sheet */
/* for an example). */
/* */
/* Bit 4 comes from the output of the divide by 1024 */
/* 0, 1, 0, 1, 0, 1, 0, 1, 0, 1 */
/* Bit 3 comes from the QC output of the LS90 producing a sequence of */
/* 0, 0, 1, 1, 0, 0, 1, 1, 1, 0 */
/* Bit 6 comes from the QD output of the LS90 producing a sequence of */
/* 0, 0, 0, 0, 1, 0, 0, 0, 0, 1 */
/* Bit 7 comes from the QA output of the LS90 producing a sequence of */
/* 0, 0, 0, 0, 0, 1, 1, 1, 1, 1 */
static int frogger_timer[10] =
{
0x00, 0x10, 0x08, 0x18, 0x40, 0x90, 0x88, 0x98, 0x88, 0xd0
};
READ_HANDLER( frogger_portB_r )
{
/* need to protect from totalcycles overflow */
static int last_totalcycles = 0;
/* number of Z80 clock cycles to count */
static int clock;
int current_totalcycles;
current_totalcycles = cpu_gettotalcycles();
clock = (clock + (current_totalcycles-last_totalcycles)) % 5120;
last_totalcycles = current_totalcycles;
return frogger_timer[clock/512];
}
WRITE_HANDLER( frogger_sh_irqtrigger_w )
{
static int last;
if (last == 0 && (data & 0x08) != 0)
{
/* setting bit 3 low then high triggers IRQ on the sound CPU */
cpu_cause_interrupt(1,0xff);
}
last = data & 0x08;
}
WRITE_HANDLER( frogger2_sh_irqtrigger_w )
{
static int last;
if (last == 0 && (data & 0x01) != 0)
{
/* setting bit 0 low then high triggers IRQ on the sound CPU */
cpu_cause_interrupt(1,0xff);
}
last = data & 0x01;
}