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gyruss.c
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C/C++ Source or Header
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2000-04-04
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2KB
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88 lines
#include "driver.h"
#include "cpu/i8039/i8039.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 */
/* 10240, formed by a standard divide by 1024, */
/* followed by a divide by 10 using a 4 bit */
/* bi-quinary count sequence. (See LS90 data sheet */
/* for an example). */
/* */
/* Bit 0 comes from the output of the divide by 1024 */
/* 0, 1, 0, 1, 0, 1, 0, 1, 0, 1 */
/* Bit 1 comes from the QC output of the LS90 producing a sequence of */
/* 0, 0, 1, 1, 0, 0, 1, 1, 1, 0 */
/* Bit 2 comes from the QD output of the LS90 producing a sequence of */
/* 0, 0, 0, 0, 1, 0, 0, 0, 0, 1 */
/* Bit 3 comes from the QA output of the LS90 producing a sequence of */
/* 0, 0, 0, 0, 0, 1, 1, 1, 1, 1 */
static int gyruss_timer[10] =
{
0x00, 0x01, 0x02, 0x03, 0x04, 0x09, 0x0a, 0x0b, 0x0a, 0x0d
};
READ_HANDLER( gyruss_portA_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)) % 10240;
last_totalcycles = current_totalcycles;
return gyruss_timer[clock/1024];
}
static void filter_w(int chip,int data)
{
int i;
for (i = 0;i < 3;i++)
{
int C;
C = 0;
if (data & 1) C += 47000; /* 47000pF = 0.047uF */
if (data & 2) C += 220000; /* 220000pF = 0.22uF */
data >>= 2;
set_RC_filter(3*chip + i,1000,2200,200,C);
}
}
WRITE_HANDLER( gyruss_filter0_w )
{
filter_w(0,data);
}
WRITE_HANDLER( gyruss_filter1_w )
{
filter_w(1,data);
}
WRITE_HANDLER( gyruss_sh_irqtrigger_w )
{
/* writing to this register triggers IRQ on the sound CPU */
cpu_cause_interrupt(1,0xff);
}
WRITE_HANDLER( gyruss_i8039_irq_w )
{
cpu_cause_interrupt(2,I8039_EXT_INT);
}