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-rw-r--r--src/mame/audio/hitme.c80
1 files changed, 80 insertions, 0 deletions
diff --git a/src/mame/audio/hitme.c b/src/mame/audio/hitme.c
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+++ b/src/mame/audio/hitme.c
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+/*************************************************************************
+
+ audio\hitme.c
+
+*************************************************************************/
+#include "driver.h"
+#include "hitme.h"
+#include "sound/discrete.h"
+
+
+static const discrete_555_desc desc_hitme_555 =
+{
+ DISC_555_OUT_SQW | DISC_555_OUT_DC,
+ 5, // B+ voltage of 555
+ DEFAULT_555_VALUES
+};
+
+static const discrete_comp_adder_table desc_hitme_adder =
+{
+ DISC_COMP_P_CAPACITOR, 0, 5,
+ {
+ 0.100e-6, // C19
+ 0.022e-6, // C18
+ 0.033e-6, // C17
+ 0.010e-6, // C16
+ 0.005e-6 // C15
+ }
+};
+
+/* Nodes - Adjustment */
+#define HITME_GAME_SPEED NODE_05
+/* Nodes - Sounds */
+#define HITME_FINAL_SND NODE_90
+
+
+DISCRETE_SOUND_START(hitme)
+
+ /* These are the inputs; PULSE-type inputs are used for oneshot latching signals */
+ DISCRETE_INPUT_DATA (HITME_DOWNCOUNT_VAL)
+ DISCRETE_INPUT_PULSE(HITME_OUT0, 0)
+ DISCRETE_INPUT_DATA (HITME_ENABLE_VAL)
+ DISCRETE_INPUT_PULSE(HITME_OUT1, 0)
+
+ /* This represents the resistor at R3, which controls the speed of the sound effects */
+ DISCRETE_ADJUSTMENT_TAG(HITME_GAME_SPEED,1,0.0,25000.0,DISC_LINADJ,"R3")
+
+ /* The clock for the main downcounter is a "404", or LS123 retriggerable multivibrator.
+ * It is clocked by IPH2 (8.945MHz/16 = 559kHz), then triggers a pulse which is adjustable
+ * via the resistor R3. When the pulse is finished, it immediately retriggers itself to
+ * form a clock. The length of the clock pulse is 0.45*R*C, where R is the variable R3
+ * resistor value, and C is 6.8uF. Thus the frequency of the resulting wave is
+ * 1.0/(0.45*R*C). We compute that frequency and use a standard 50% duty cycle square wave.
+ * This is because the "off time" of the clock is very small (559kHz), and we will miss
+ * edges if we model it perfectly accurately. */
+ DISCRETE_TRANSFORM3(NODE_16,1,1,0.45*6.8e-6,HITME_GAME_SPEED,"012*/")
+ DISCRETE_SQUAREWAVE(NODE_17,1,NODE_16,1,50,0.5,0)
+
+ /* There are 2 cascaded 4-bit downcounters (2R = low, 2P = high), effectively
+ * making an 8-bit downcounter, clocked by the clock from the 404 chip.
+ * The initial count is latched by writing OUT0. */
+ DISCRETE_COUNTER(NODE_20,1,HITME_OUT0,NODE_17,255,0,HITME_DOWNCOUNT_VAL,DISC_CLK_ON_F_EDGE)
+ /* When the counter rolls over from 0->255, we clock a D-type flipflop at 2N. */
+ DISCRETE_TRANSFORM2(NODE_21,1,NODE_20,255,"01=!")
+
+ /* This flipflop represents the latch at 1L. It is clocked when OUT1 is written and latches
+ * the value from the processor. When the downcounter above rolls over, it clears the latch. */
+ DISCRETE_LOGIC_DFLIPFLOP(NODE_22,1,NODE_21,1,HITME_OUT1,HITME_ENABLE_VAL)
+
+ /* The output of the latch goes through a series of various capacitors in parallel. */
+ DISCRETE_COMP_ADDER(NODE_23,1,NODE_22,&desc_hitme_adder)
+
+ /* The combined capacitance is input to a 555 timer in astable mode. */
+ DISCRETE_555_ASTABLE(NODE_24,1,22e3,39e3,NODE_23,&desc_hitme_555)
+
+ /* The output of the 555 timer is fed through a simple CR filter in the amp stage. */
+ DISCRETE_CRFILTER(HITME_FINAL_SND,1,NODE_24,1e3,50e-6)
+
+ /* We scale the final output of 3.3 to 16-bit range and output it at full volume */
+ DISCRETE_OUTPUT(HITME_FINAL_SND,32000.0/3.3)
+DISCRETE_SOUND_END