// license:BSD-3-Clause // copyright-holders:Aaron Giles /************************************************************************* audio\hitme.c *************************************************************************/ #include "emu.h" #include "includes/hitme.h" #include "sound/discrete.h" static const discrete_555_desc desc_hitme_555 = { DISC_555_OUT_ENERGY | 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_discrete) /* 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(HITME_GAME_SPEED,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_16,1,0.45*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_17,0,255,0,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,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,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,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,NODE_24,1e3,50e-6) /* We scale the final output of 3.8 to 16-bit range and output it at full volume */ DISCRETE_OUTPUT(HITME_FINAL_SND,32000.0/3.8) DISCRETE_SOUND_END