1 /****************************************************************************
2 *
3 * geebee.c
4 *
5 * sound driver
6 * juergen buchmueller <pullmoll@t-online.de>, jan 2000
7 *
8 ****************************************************************************/
9
10 #include <math.h>
11 #include "driver.h"
12
13 static void *volume_timer = NULL;
14 static UINT16 *decay = NULL;
15 static int channel;
16 static int sound_latch = 0;
17 static int sound_signal = 0;
18 static int volume = 0;
19 static int noise = 0;
20
volume_decay(int param)21 static void volume_decay(int param)
22 {
23 if( --volume < 0 )
24 volume = 0;
25 }
26
WRITE_HANDLER(geebee_sound_w)27 WRITE_HANDLER( geebee_sound_w )
28 {
29 stream_update(channel,0);
30 sound_latch = data;
31 volume = 0x7fff; /* set volume */
32 noise = 0x0000; /* reset noise shifter */
33 /* faster decay enabled? */
34 if( sound_latch & 8 )
35 {
36 /*
37 * R24 is 10k, Rb is 0, C57 is 1uF
38 * charge time t1 = 0.693 * (R24 + Rb) * C57 -> 0.22176s
39 * discharge time t2 = 0.693 * (Rb) * C57 -> 0
40 * Then C33 is only charged via D6 (1N914), not discharged!
41 * Decay:
42 * discharge C33 (1uF) through R50 (22k) -> 0.14058s
43 */
44 if( volume_timer )
45 timer_remove(volume_timer);
46 volume_timer = timer_pulse(TIME_IN_HZ(32768/0.14058), 0, volume_decay);
47 }
48 else
49 {
50 /*
51 * discharge only after R49 (100k) in the amplifier section,
52 * so the volume shouldn't very fast and only when the signal
53 * is gated through 6N (4066).
54 * I can only guess here that the decay should be slower,
55 * maybe half as fast?
56 */
57 if( volume_timer )
58 timer_remove(volume_timer);
59 volume_timer = timer_pulse(TIME_IN_HZ(32768/0.2906), 0, volume_decay);
60 }
61 }
62
geebee_sound_update(int param,INT16 * buffer,int length)63 static void geebee_sound_update(int param, INT16 *buffer, int length)
64 {
65 static int vcarry = 0;
66 static int vcount = 0;
67
68 while (length--)
69 {
70 *buffer++ = sound_signal;
71 /* 1V = HSYNC = 18.432MHz / 3 / 2 / 384 = 8000Hz */
72 vcarry -= 18432000 / 3 / 2 / 384;
73 while (vcarry < 0)
74 {
75 vcarry += Machine->sample_rate;
76 vcount++;
77 /* noise clocked with raising edge of 2V */
78 if ((vcount & 3) == 2)
79 {
80 /* bit0 = bit0 ^ !bit10 */
81 if ((noise & 1) == ((noise >> 10) & 1))
82 noise = ((noise << 1) & 0xfffe) | 1;
83 else
84 noise = (noise << 1) & 0xfffe;
85 }
86 switch (sound_latch & 7)
87 {
88 case 0: /* 4V */
89 sound_signal = (vcount & 0x04) ? decay[volume] : 0;
90 break;
91 case 1: /* 8V */
92 sound_signal = (vcount & 0x08) ? decay[volume] : 0;
93 break;
94 case 2: /* 16V */
95 sound_signal = (vcount & 0x10) ? decay[volume] : 0;
96 break;
97 case 3: /* 32V */
98 sound_signal = (vcount & 0x20) ? decay[volume] : 0;
99 break;
100 case 4: /* TONE1 */
101 sound_signal = !(vcount & 0x01) && !(vcount & 0x10) ? decay[volume] : 0;
102 break;
103 case 5: /* TONE2 */
104 sound_signal = !(vcount & 0x02) && !(vcount & 0x20) ? decay[volume] : 0;
105 break;
106 case 6: /* TONE3 */
107 sound_signal = !(vcount & 0x04) && !(vcount & 0x40) ? decay[volume] : 0;
108 break;
109 default: /* NOISE */
110 /* QH of 74164 #4V */
111 sound_signal = (noise & 0x8000) ? decay[volume] : 0;
112 }
113 }
114 }
115 }
116
geebee_sh_start(const struct MachineSound * msound)117 int geebee_sh_start(const struct MachineSound *msound)
118 {
119 int i;
120
121 decay = (UINT16 *)malloc(32768 * sizeof(INT16));
122 if( !decay )
123 return 1;
124
125 for( i = 0; i < 0x8000; i++ )
126 decay[0x7fff-i] = (INT16) (0x7fff/exp(1.0*i/4096));
127
128 channel = stream_init("GeeBee", 100, Machine->sample_rate, 0, geebee_sound_update);
129 return 0;
130 }
131
geebee_sh_stop(void)132 void geebee_sh_stop(void)
133 {
134 if( volume_timer )
135 timer_remove(volume_timer);
136 volume_timer = NULL;
137 if( decay )
138 free(decay);
139 decay = NULL;
140 }
141
geebee_sh_update(void)142 void geebee_sh_update(void)
143 {
144 stream_update(channel,0);
145 }
146