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sndhrdw
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geebee.c
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C/C++ Source or Header
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2000-04-04
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4KB
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146 lines
/****************************************************************************
*
* geebee.c
*
* sound driver
* juergen buchmueller <pullmoll@t-online.de>, jan 2000
*
****************************************************************************/
#include <math.h>
#include "driver.h"
static void *volume_timer = NULL;
static UINT16 *decay = NULL;
static int channel;
static int sound_latch = 0;
static int sound_signal = 0;
static int volume = 0;
static int noise = 0;
static void volume_decay(int param)
{
if( --volume < 0 )
volume = 0;
}
WRITE_HANDLER( geebee_sound_w )
{
stream_update(channel,0);
sound_latch = data;
volume = 0x7fff; /* set volume */
noise = 0x0000; /* reset noise shifter */
/* faster decay enabled? */
if( sound_latch & 8 )
{
/*
* R24 is 10k, Rb is 0, C57 is 1uF
* charge time t1 = 0.693 * (R24 + Rb) * C57 -> 0.22176s
* discharge time t2 = 0.693 * (Rb) * C57 -> 0
* Then C33 is only charged via D6 (1N914), not discharged!
* Decay:
* discharge C33 (1uF) through R50 (22k) -> 0.14058s
*/
if( volume_timer )
timer_remove(volume_timer);
volume_timer = timer_pulse(TIME_IN_HZ(32768/0.14058), 0, volume_decay);
}
else
{
/*
* discharge only after R49 (100k) in the amplifier section,
* so the volume shouldn't very fast and only when the signal
* is gated through 6N (4066).
* I can only guess here that the decay should be slower,
* maybe half as fast?
*/
if( volume_timer )
timer_remove(volume_timer);
volume_timer = timer_pulse(TIME_IN_HZ(32768/0.2906), 0, volume_decay);
}
}
static void geebee_sound_update(int param, INT16 *buffer, int length)
{
static int vcarry = 0;
static int vcount = 0;
while (length--)
{
*buffer++ = sound_signal;
/* 1V = HSYNC = 18.432MHz / 3 / 2 / 384 = 8000Hz */
vcarry -= 18432000 / 3 / 2 / 384;
while (vcarry < 0)
{
vcarry += Machine->sample_rate;
vcount++;
/* noise clocked with raising edge of 2V */
if ((vcount & 3) == 2)
{
/* bit0 = bit0 ^ !bit10 */
if ((noise & 1) == ((noise >> 10) & 1))
noise = ((noise << 1) & 0xfffe) | 1;
else
noise = (noise << 1) & 0xfffe;
}
switch (sound_latch & 7)
{
case 0: /* 4V */
sound_signal = (vcount & 0x04) ? decay[volume] : 0;
break;
case 1: /* 8V */
sound_signal = (vcount & 0x08) ? decay[volume] : 0;
break;
case 2: /* 16V */
sound_signal = (vcount & 0x10) ? decay[volume] : 0;
break;
case 3: /* 32V */
sound_signal = (vcount & 0x20) ? decay[volume] : 0;
break;
case 4: /* TONE1 */
sound_signal = !(vcount & 0x01) && !(vcount & 0x10) ? decay[volume] : 0;
break;
case 5: /* TONE2 */
sound_signal = !(vcount & 0x02) && !(vcount & 0x20) ? decay[volume] : 0;
break;
case 6: /* TONE3 */
sound_signal = !(vcount & 0x04) && !(vcount & 0x40) ? decay[volume] : 0;
break;
default: /* NOISE */
/* QH of 74164 #4V */
sound_signal = (noise & 0x8000) ? decay[volume] : 0;
}
}
}
}
int geebee_sh_start(const struct MachineSound *msound)
{
int i;
decay = (UINT16 *)malloc(32768 * sizeof(INT16));
if( !decay )
return 1;
for( i = 0; i < 0x8000; i++ )
decay[0x7fff-i] = (INT16) (0x7fff/exp(1.0*i/4096));
channel = stream_init("GeeBee", 100, Machine->sample_rate, 0, geebee_sound_update);
return 0;
}
void geebee_sh_stop(void)
{
if( volume_timer )
timer_remove(volume_timer);
volume_timer = NULL;
if( decay )
free(decay);
decay = NULL;
}
void geebee_sh_update(void)
{
stream_update(channel,0);
}