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-rw-r--r--src/mame/audio/geebee.c130
1 files changed, 130 insertions, 0 deletions
diff --git a/src/mame/audio/geebee.c b/src/mame/audio/geebee.c
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+++ b/src/mame/audio/geebee.c
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+/****************************************************************************
+ *
+ * geebee.c
+ *
+ * sound driver
+ * juergen buchmueller <pullmoll@t-online.de>, jan 2000
+ *
+ ****************************************************************************/
+
+#include <math.h>
+#include "driver.h"
+#include "streams.h"
+#include "sound/custom.h"
+#include "includes/warpwarp.h"
+
+static emu_timer *volume_timer = NULL;
+static UINT16 *decay = NULL;
+static sound_stream *channel;
+static int sound_latch = 0;
+static int sound_signal = 0;
+static int volume = 0;
+static int noise = 0;
+static int vcount = 0;
+
+static TIMER_CALLBACK( volume_decay )
+{
+ if( --volume < 0 )
+ volume = 0;
+}
+
+WRITE8_HANDLER( geebee_sound_w )
+{
+ stream_update(channel);
+ 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
+ */
+ attotime period = attotime_div(attotime_mul(ATTOTIME_IN_HZ(32768), 14058), 100000);
+ timer_adjust(volume_timer, period, 0, period);
+ }
+ 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?
+ */
+ attotime period = attotime_div(attotime_mul(ATTOTIME_IN_HZ(32768), 29060), 100000);
+ timer_adjust(volume_timer, period, 0, period);
+ }
+}
+
+static void geebee_sound_update(void *param, stream_sample_t **inputs, stream_sample_t **outputs, int length)
+{
+ stream_sample_t *buffer = outputs[0];
+
+ while (length--)
+ {
+ *buffer++ = sound_signal;
+ /* 1V = HSYNC = 18.432MHz / 3 / 2 / 384 = 8000Hz */
+ {
+ 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;
+ }
+ }
+ }
+}
+
+void *geebee_sh_start(int clock, const struct CustomSound_interface *config)
+{
+ int i;
+
+ decay = (UINT16 *)auto_malloc(32768 * sizeof(INT16));
+
+ for( i = 0; i < 0x8000; i++ )
+ decay[0x7fff-i] = (INT16) (0x7fff/exp(1.0*i/4096));
+
+ /* 1V = HSYNC = 18.432MHz / 3 / 2 / 384 = 8000Hz */
+ channel = stream_create(0, 1, 18432000 / 3 / 2 / 384, NULL, geebee_sound_update);
+ vcount = 0;
+
+ volume_timer = timer_alloc(volume_decay);
+ return auto_malloc(1);
+}