shrooms-vb-core/core/vb.c

861 lines
26 KiB
C

#ifndef VBAPI
#define VBAPI
#endif
#include <float.h>
#include <vb.h>
/*********************************** Types ***********************************/
/* Output image */
typedef uint8_t Pixels[2][384*224];
/* VSU channel */
typedef struct {
/* Envelope */
struct {
/* Register state */
uint8_t enb; /* Modifications enabled */
uint8_t dir; /* Modification direction */
uint8_t interval; /* Modification interval */
uint8_t rep; /* Repeat modifications */
uint8_t value; /* Master output level */
/* Other state */
uint32_t clocks; /* Clocks until modification */
uint8_t reload; /* Automatic reload value */
} env;
/* Frequency */
struct {
uint16_t current; /* Current value */
uint16_t written; /* Last value written */
} freq;
/* Stereo levels */
struct {
uint8_t left; /* Left output level */
uint8_t right; /* Right output level */
} lrv;
/* Control */
struct {
/* Register state */
uint8_t auto_; /* Shutoff enabled */
uint8_t enb; /* Sound generation enabled */
uint8_t interval; /* Shutoff interval */
/* Other state */
uint32_t clocks; /* Clocks until shutoff */
} int_;
/* Waveform */
struct {
/* Register state */
uint8_t wave; /* Waveform index */
/* Other state */
int sample; /* Current sample index */
} wave;
/* Other state */
uint32_t clocks; /* Clocks until next wave or noise sample */
uint8_t freqmod; /* Frequency modifications are active */
uint32_t until; /* Clocks until channel component update */
} Channel;
/* Simulation state */
struct VB {
/* Game Pak */
struct {
uint8_t *ram; /* Save RAM */
uint8_t *rom; /* Program ROM */
uint32_t ramMask; /* Size of SRAM - 1 */
uint32_t romMask; /* Size of ROM - 1 */
} cart;
/* CPU */
struct {
/* Cache Control Word */
struct {
uint8_t ice; /* Instruction Cache Enable */
} chcw;
/* Exception Cause Register */
struct {
uint16_t eicc; /* Exception/Interrupt Cause Code */
uint16_t fecc; /* Fatal Error Cause Code */
} ecr;
/* Program Status Word */
struct {
uint8_t ae; /* Address Trap Enable */
uint8_t cy; /* Carry */
uint8_t ep; /* Exception Pending */
uint8_t fiv; /* Floating Invalid */
uint8_t fov; /* Floating Overflow */
uint8_t fpr; /* Floading Precision */
uint8_t fro; /* Floating Reserved Operand */
uint8_t fud; /* Floading Underflow */
uint8_t fzd; /* Floating Zero Divide */
uint8_t i; /* Interrupt Level */
uint8_t id; /* Interrupt Disable */
uint8_t np; /* NMI Pending */
uint8_t ov; /* Overflow */
uint8_t s; /* Sign */
uint8_t z; /* Zero */
} psw;
/* Other registers */
uint32_t adtre; /* Address Trap Register for Execution */
uint32_t eipc; /* Exception/Interrupt PC */
uint32_t eipsw; /* Exception/Interrupt PSW */
uint32_t fepc; /* Fatal Error PC */
uint32_t fepsw; /* Fatal Error PSW */
uint32_t pc; /* Program Counter */
int32_t program[32]; /* Program registers */
uint32_t sr29; /* System register 29 */
uint32_t sr31; /* System register 31 */
/* Working data */
union {
struct {
uint32_t dest;
uint64_t src;
} bs; /* Arithmetic bit strings */
struct {
uint32_t address;
int32_t value;
} data; /* Data accesses */
} aux;
/* Other state */
uint32_t clocks; /* Master clocks to wait */
uint16_t code[2]; /* Instruction code units */
uint16_t exception; /* Exception cause code */
int halt; /* CPU is halting */
uint16_t irq; /* Interrupt request lines */
int length; /* Instruction code length */
uint32_t nextPC; /* Address of next instruction */
int operation; /* Current operation ID */
int step; /* Operation sub-task ID */
} cpu;
/* Communication port */
struct {
/* Register state */
uint8_t c_clk_sel; /* Transmission clock source */
uint8_t c_int_inh; /* Interrupt acknowledge/disable */
uint8_t c_stat; /* Communication is underway */
uint8_t cc_int_inh; /* Interrupt acknowledge/disable */
uint8_t cc_int_lev; /* Interrupt condition */
uint8_t cc_rd; /* Manual read */
uint8_t cc_sig; /* Automatic write */
uint8_t cc_smp; /* Automatic read */
uint8_t cc_wr; /* Manual write */
uint8_t cdrr; /* Data received */
uint8_t cdtr; /* Data to transmit */
/* Other state */
int8_t c_irq; /* COM interrupt request */
int8_t cc_irq; /* COMCNT interrupt request */
uint32_t clocks; /* Master clocks to wait */
} ext;
/* Game pad */
struct {
/* Register state */
uint8_t k_int_inh; /* Interrupt acknowledge/disable */
uint8_t para_si; /* Read reset signal */
uint8_t s_abt_dis; /* Abort hardware read */
uint8_t sdhr; /* High key bits */
uint8_t sdlr; /* Low key bits */
uint32_t si_stat; /* Hardware read in progress */
uint8_t soft_ck; /* Controller communication signal */
/* Other state */
uint32_t clocks; /* Master clocks to wait */
uint16_t keys; /* Next input bits */
int step; /* Software read processing phase */
} pad;
/* Timer */
struct {
/* Register state */
uint8_t t_clk_sel; /* Counter tick duration */
uint8_t t_enb; /* Enable timer */
uint8_t tim_z_int; /* Enable interrupt */
uint8_t z_stat; /* Zero status */
/* Other state */
uint32_t clocks; /* Master clocks to wait */
uint16_t counter; /* Current counter value */
uint16_t reload; /* Reload counter value */
uint32_t until; /* Clocks until interrupt condition */
} tmr;
/* VIP */
struct {
/* CTA */
struct {
uint8_t cta_l; /* Left column table index */
uint8_t cta_r; /* Right column table index */
} cta;
/* Display processor */
struct {
/* Register state */
uint8_t disp; /* Display enabled */
uint8_t fclk; /* Frame clock signal high */
uint8_t l0bsy; /* Displaying left frame buffer 0 */
uint8_t l1bsy; /* Displaying left frame buffer 1 */
uint8_t lock; /* Lock CTA */
uint8_t r0bsy; /* Displaying right frame buffer 0 */
uint8_t r1bsy; /* Displaying right frame buffer 1*/
uint8_t re; /* Memory refresh enabled */
uint8_t scanrdy; /* Mirrors are stable */
uint8_t synce; /* Servo enabled */
/* Other state */
uint8_t brt[4]; /* Precomputed brightness */
int buffer; /* Index of frame buffer to display */
uint32_t clocks; /* Master clocks to wait */
int column; /* Index of column to display */
uint32_t cta; /* Column table pointer in memory */
uint8_t enabled; /* Was enabled at FCLK */
uint32_t fbDest; /* Output frame pixel address */
uint32_t fbSrc; /* Source frame buffer address */
int32_t repeat; /* Current column table repeat value */
int step; /* Processing phase */
uint32_t until; /* Clocks until interrupt condition */
} dp;
/* Pixel processor */
struct {
/* Register state */
uint8_t f0bsy; /* Drawing into frame buffer 0 */
uint8_t f1bsy; /* Drawing into frame buffer 1 */
uint8_t overtime; /* Drawing extends into display interval */
uint8_t sbcmp; /* Vertical output position compare */
uint8_t sbcount; /* Current vertical output position */
uint32_t sbout; /* Drawing specified vertical output position */
uint8_t xpen; /* Drawing enabled */
/* Other state */
uint32_t clocks; /* Master clocks to wait */
int column; /* Current horizontal output position */
uint8_t enabled; /* Was enabled at FCLK */
int frame; /* FRMCYC counter */
int32_t halfword; /* Current output halfword offset */
int step; /* Processing phase */
uint32_t until; /* Clocks until interrupt condition */
} xp;
/* Control state */
uint8_t bkcol; /* Backdrop color */
uint8_t brtRest[4]; /* Brightness and REST */
uint8_t frmcyc; /* Game frame control */
uint8_t gplt[4][4]; /* Background palettes */
uint16_t intenb; /* Interrupts enabled */
uint16_t intpnd; /* Interrupts pending */
uint8_t jplt[4][4]; /* Object palettes */
uint16_t spt[4]; /* Object control */
/* Rendering shadow memory */
uint16_t halfwords[384*28]; /* Output timing by 1x8 halfword */
Pixels output[2]; /* Output images, row-major */
Pixels shadow; /* Drawing shadow image, column-major */
/* Other state */
uint8_t ram[0x40000]; /* Video memory */
} vip;
/* VSU */
struct {
/* Audio sources */
Channel channels[6];
/* Channel 5 frequency modification */
struct {
/* Register state */
uint8_t clk; /* Base modification clock */
uint8_t dir; /* Sweep direction */
uint8_t enb; /* Modifications enabled */
uint8_t func; /* Modification function */
uint8_t interval; /* Modification interval */
uint8_t rep; /* Repeat modulation */
uint8_t shift; /* Sweep shift amount */
/* Other state */
uint32_t clocks; /* Clocks until modification */
uint16_t next; /* Next frequency value */
int sample; /* Current sample index */
} freqmod;
/* Channel 6 noise generator */
struct {
/* Register state */
uint8_t tap; /* LSFR feedback bit position */
/* Other state */
uint16_t register_; /* Pseudorandom bits */
} noise;
/* Sample output */
struct {
float i1[2]; /* Previous analog input sample */
float o1[2]; /* Previous analog output sample */
unsigned capacity; /* Number of audio frames in output buffer */
unsigned offset; /* Position in output buffer */
void *samples; /* Output buffer */
int type; /* Output data type */
} out;
/* Memory */
int8_t modulation[32]; /* Modulation amounts */
uint8_t waves[5][32]; /* Wafeform samples */
/* Other state */
uint32_t clocks; /* Clocks until next output sample */
int sample; /* Output sample index, period 417 */
} vsu;
/* Wait controller */
struct {
uint8_t exp1w; /* Cartridge expansion 1-wait */
uint8_t rom1w; /* Cartridge ROM 1-wait */
} wcr;
/* Pseudo-halt */
struct {
uint32_t address; /* Monitor address */
uint8_t enabled; /* Pseudo-halt function is enabled */
uint8_t operation; /* Monitoring operation */
uint8_t step; /* Number of consecutive matching reads */
int type; /* Memory access type */
int32_t value; /* Value read from monitor address */
/* CPU snapshot */
uint32_t adtre;
uint32_t chcw;
uint32_t ecr;
uint32_t eipc;
uint32_t eipsw;
uint32_t fepc;
uint32_t fepsw;
uint32_t pc;
int32_t program[31];
uint32_t psw;
uint32_t sr29;
uint32_t sr31;
} ph;
/* Other state */
uint8_t wram[0x10000]; /* System RAM */
/* Application data */
vbOnException onException; /* CPU exception */
vbOnExecute onExecute; /* CPU instruction execute */
vbOnFetch onFetch; /* CPU instruction fetch */
vbOnFrame onFrame; /* VIP frame ready */
vbOnLink onLink; /* Communication transfer */
vbOnRead onRead; /* CPU instruction read */
vbOnSamples onSamples; /* VSU samples full */
vbOnWrite onWrite; /* CPU instruction write */
VB *peer; /* Communication peer */
void *tag; /* User data */
};
/***************************** Library Functions *****************************/
/* Sign-extend an integer of variable width */
static int32_t SignExtend(int32_t value, int32_t bits) {
#ifndef VB_SIGNED_PROPAGATE
value &= ~((uint32_t) 0xFFFFFFFF << bits);
bits = (int32_t) 1 << (bits - (int32_t) 1);
return (value ^ bits) - bits;
#else
return value << (32 - bits) >> (32 - bits);
#endif
}
/******************************** Sub-Modules ********************************/
#include "ext.c"
#include "game-pad.c"
#include "timer.c"
#include "bus.c"
#include "cpu.c"
#include "vip.c"
#include "vsu.c"
#include "pseudo-halt.c"
/***************************** Library Functions *****************************/
/* Process a simulation for a given number of clocks */
static int sysEmulate(VB *sim, uint32_t clocks) {
int ret = 0;
/* CPU is in a pseudo-halt state that requires an interrupt to exit */
int never =
sim->cpu.operation == CPU_PHALT &&
sim->ph.operation == PH_NEVER
;
/* Process all components */
if (!never){ret = cpuEmulate(sim, clocks);}
ret |= extEmulate(sim, clocks);
padEmulate(sim, clocks);
tmrEmulate(sim, clocks);
vsuEmulate(sim, clocks);
ret |= vipEmulate(sim, clocks);
if ( never) ret |= cpuEmulate(sim, clocks);
return ret;
}
/* Determine how many clocks are guaranteed to process */
static uint32_t sysUntil(VB *sim, uint32_t clocks) {
clocks = cpuUntil(sim, clocks);
clocks = extUntil(sim, clocks);
clocks = padUntil(sim, clocks);
clocks = tmrUntil(sim, clocks);
clocks = vipUntil(sim, clocks);
return clocks;
}
/******************************* API Commands ********************************/
/* Process one simulation */
VBAPI int vbEmulate(VB *sim, uint32_t *clocks) {
int brk; /* A callback requested a break */
uint32_t until; /* Clocks guaranteed to process */
while (*clocks != 0) {
until = sysUntil(sim, *clocks);
brk = sysEmulate(sim, until);
*clocks -= until;
if (brk)
return brk; /* TODO: return 1 */
}
return 0;
}
/* Process multiple simulations */
VBAPI int vbEmulateEx(VB **sims, unsigned count, uint32_t *clocks) {
int brk; /* A callback requested a break */
uint32_t until; /* Clocks guaranteed to process */
unsigned x; /* Iterator */
/* Process one simulation */
if (count == 1)
return vbEmulate(sims[0], clocks);
/* Process multiple simulations */
while (*clocks != 0) {
until = *clocks;
for (x = count; x > 0; x--)
until = sysUntil(sims[x - 1], until);
brk = 0;
for (x = count; x > 0; x--)
brk |= sysEmulate(sims[x - 1], until);
*clocks -= until;
if (brk)
return brk; /* TODO: return 1 */
}
return 0;
}
/* Retrieve the game pack RAM buffer */
VBAPI void* vbGetCartRAM(VB *sim, uint32_t *size) {
if (size != NULL)
*size = sim->cart.ram == NULL ? 0 : sim->cart.ramMask + 1;
return sim->cart.ram;
}
/* Retrieve the game pack ROM buffer */
VBAPI void* vbGetCartROM(VB *sim, uint32_t *size) {
if (size != NULL)
*size = sim->cart.rom == NULL ? 0 : sim->cart.romMask + 1;
return sim->cart.rom;
}
/* Retrieve the exception callback handler */
VBAPI vbOnException vbGetExceptionCallback(VB *sim) {
return sim->onException;
}
/* Retrieve the execute callback handler */
VBAPI vbOnExecute vbGetExecuteCallback(VB *sim) {
return sim->onExecute;
}
/* Retrieve the fetch callback handler */
VBAPI vbOnFetch vbGetFetchCallback(VB *sim) {
return sim->onFetch;
}
/* Retrieve the frame callback handler */
VBAPI vbOnFrame vbGetFrameCallback(VB *sim) {
return sim->onFrame;
}
/* Retrieve the current game pad key state */
VBAPI uint16_t vbGetKeys(VB *sim) {
return sim->pad.keys;
}
/* Retrieve the current link callback handler */
VBAPI vbOnLink vbGetLinkCallback(VB *sim) {
return sim->onLink;
}
/* Retrieve a core option value */
VBAPI int vbGetOption(VB *sim, int key) {
switch (key) {
case VB_PSEUDO_HALT: return sim->ph.enabled;
}
return 0;
}
/* Retrieve the communication peer */
VBAPI VB* vbGetPeer(VB *sim) {
return sim->peer;
}
/* Retrieve the most recent frame image pixels */
VBAPI void vbGetPixels(VB *sim, void *left, int leftStrideX, int leftStrideY,
void *right, int rightStrideX, int rightStrideY) {
uint8_t *dest; /* Output data */
int offset; /* Horizontal offset of output pixel */
uint8_t *src; /* Source data */
int xStride; /* Bytes between output pixels */
int yStride; /* Bytes between output lines */
int i, x, y; /* Iterators */
/* Process both eyes */
for (i = 0; i < 2; i++) {
/* Working variables for left image */
if (i == 0) {
dest = left;
xStride = leftStrideX;
yStride = leftStrideY;
}
/* Working variables for right image */
else {
dest = right;
xStride = rightStrideX;
yStride = rightStrideY;
}
/* Nothing to do */
if (dest == NULL)
continue;
/* Transfer pixels to the destination */
src = sim->vip.output[sim->vip.dp.buffer ^ 1][i];
for (y = 0; y < 224; y++, dest += yStride)
for (x = offset = 0; x < 384; x++, offset += xStride)
dest[offset] = *src++;
}
}
/* Retrieve the value of the program counter */
VBAPI uint32_t vbGetProgramCounter(VB *sim) {
return sim->cpu.pc;
}
/* Retrieve the value in a program register */
VBAPI int32_t vbGetProgramRegister(VB *sim, unsigned index) {
return index < 1 || index > 31 ? 0 : sim->cpu.program[index];
}
/* Retrieve the read callback handler */
VBAPI vbOnRead vbGetReadCallback(VB *sim) {
return sim->onRead;
}
/* Retrieve the audio samples buffer */
VBAPI void* vbGetSamples(VB *sim, int *type,
unsigned *capacity, unsigned *position) {
if (sim->vsu.out.samples == NULL) {
if (type != NULL)
*type = 0;
if (capacity != NULL)
*capacity = 0;
if (position != NULL)
*position = 0;
} else {
if (type != NULL)
*type = sim->vsu.out.type;
if (capacity != NULL)
*capacity = sim->vsu.out.capacity;
if (position != NULL)
*position = sim->vsu.out.offset >> 1;
}
return sim->vsu.out.samples;
}
/* Retrieve the samples callback handler */
VBAPI vbOnSamples vbGetSamplesCallback(VB *sim) {
return sim->onSamples;
}
/* Retrieve the value in a system register */
VBAPI uint32_t vbGetSystemRegister(VB *sim, unsigned index) {
return index > 31 ? 0 : cpuGetSystemRegister(sim, index);
}
/* Retrieve a simulation's userdata pointer */
VBAPI void* vbGetUserData(VB *sim) {
return sim->tag;
}
/* Retrieve the write callback handler */
VBAPI vbOnWrite vbGetWriteCallback(VB *sim) {
return sim->onWrite;
}
/* Initialize a simulation instance */
VBAPI VB* vbInit(VB *sim) {
sim->cart.ram = NULL;
sim->cart.rom = NULL;
sim->ph.enabled = 0;
sim->vsu.out.samples = NULL;
sim->onExecute = NULL;
sim->onFetch = NULL;
sim->onFrame = NULL;
sim->onLink = NULL;
sim->onRead = NULL;
sim->onSamples = NULL;
sim->onWrite = NULL;
sim->peer = NULL;
sim->tag = NULL;
vbReset(sim);
return sim;
}
/* Read a value from the memory bus */
VBAPI int32_t vbRead(VB *sim, uint32_t address, int type) {
int32_t value;
if (type < 0 || type > 4)
return 0;
busRead(sim, address, type, &value);
return value;
}
/* Simulate a hardware reset */
VBAPI VB* vbReset(VB *sim) {
int x; /* Iterator */
/* Wait controller */
sim->wcr.exp1w = 0;
sim->wcr.rom1w = 0;
/* WRAM (the hardware does not do this) */
for (x = 0; x < 0x10000; x++)
sim->wram[x] = 0x00;
/* Components */
cpuReset(sim);
extReset(sim);
padReset(sim);
tmrReset(sim);
vipReset(sim);
vsuReset(sim);
/* Pseudo-halt */
sim->ph.step = 0;
return sim;
}
/* Specify a game pak RAM buffer */
VBAPI int vbSetCartRAM(VB *sim, void *sram, uint32_t size) {
if (sram != NULL) {
if (size < 16 || size > 0x1000000 || (size & (size - 1)) != 0)
return 1;
sim->cart.ramMask = size - 1;
}
sim->cart.ram = sram;
return 0;
}
/* Specify a game pak ROM buffer */
VBAPI int vbSetCartROM(VB *sim, void *rom, uint32_t size) {
if (rom != NULL) {
if (size < 16 || size > 0x1000000 || (size & (size - 1)) != 0)
return 1;
sim->cart.romMask = size - 1;
}
sim->cart.rom = rom;
return 0;
}
/* Specify a new exception callback handler */
VBAPI vbOnException vbSetExceptionCallback(VB *sim, vbOnException callback) {
vbOnException prev = sim->onException;
sim->onException = callback;
return prev;
}
/* Specify a new execute callback handler */
VBAPI vbOnExecute vbSetExecuteCallback(VB *sim, vbOnExecute callback) {
vbOnExecute prev = sim->onExecute;
sim->onExecute = callback;
return prev;
}
/* Specify a new fetch callback handler */
VBAPI vbOnFetch vbSetFetchCallback(VB *sim, vbOnFetch callback) {
vbOnFetch prev = sim->onFetch;
sim->onFetch = callback;
return prev;
}
/* Specify a new frame callback handler */
VBAPI vbOnFrame vbSetFrameCallback(VB *sim, vbOnFrame callback) {
vbOnFrame prev = sim->onFrame;
sim->onFrame = callback;
return prev;
}
/* Specify new game pad keys */
VBAPI uint16_t vbSetKeys(VB *sim, uint16_t keys) {
return sim->pad.keys = keys;
}
/* Specify a new link callback handler */
VBAPI vbOnLink vbSetLinkCallback(VB *sim, vbOnLink callback) {
vbOnLink prev = sim->onLink;
sim->onLink = callback;
return prev;
}
/* Specify a new core option value */
VBAPI int vbSetOption(VB *sim, int key, int value) {
switch (key) {
case VB_PSEUDO_HALT:
sim->ph.enabled = value = !!value;
if (!value) {
sim->ph.step = 0;
if (sim->cpu.operation == CPU_PHALT) {
sim->cpu.operation = CPU_FETCH;
sim->cpu.step = 0;
}
}
break;
}
return value;
}
/* Specify a new communication peer */
VBAPI void vbSetPeer(VB *sim, VB *peer) {
if (sim->peer == peer)
return;
if (sim->peer != NULL)
sim->peer->peer = NULL;
sim->peer = peer;
if (peer == NULL)
return;
if (peer->peer != NULL)
peer->peer->peer = NULL;
peer->peer = sim;
}
/* Specify a new value for the program counter */
VBAPI uint32_t vbSetProgramCounter(VB *sim, uint32_t value) {
sim->cpu.clocks = 0;
sim->cpu.operation = CPU_FETCH;
sim->cpu.pc = sim->cpu.nextPC = value & 0xFFFFFFFE;
sim->cpu.step = 0;
return sim->cpu.pc;
}
/* Specify a new value for a program register */
VBAPI int32_t vbSetProgramRegister(VB *sim, unsigned index, int32_t value) {
return index < 1 || index > 31 ? 0 : (sim->cpu.program[index] = value);
}
/* Specify a new read callback handler */
VBAPI vbOnRead vbSetReadCallback(VB *sim, vbOnRead callback) {
vbOnRead prev = sim->onRead;
sim->onRead = callback;
return prev;
}
/* Specify a new audio samples buffer */
VBAPI int vbSetSamples(VB *sim, void *samples, int type, unsigned capacity) {
if (samples != NULL &&
(capacity == 0 || (type != VB_S16 && type != VB_F32)))
return 1;
sim->vsu.out.capacity = capacity;
sim->vsu.out.offset = 0;
sim->vsu.out.samples = samples;
sim->vsu.out.type = type;
return 0;
}
/* Specify a new samples callback handler */
VBAPI vbOnSamples vbSetSamplesCallback(VB *sim, vbOnSamples callback) {
vbOnSamples prev = sim->onSamples;
sim->onSamples = callback;
return prev;
}
/* Specify a new value for a system register */
VBAPI uint32_t vbSetSystemRegister(VB *sim, unsigned index, uint32_t value) {
return index > 31 ? 0 : cpuSetSystemRegister(sim, index, value, 1);
}
/* Specify a new write callback handler */
VBAPI vbOnWrite vbSetWriteCallback(VB *sim, vbOnWrite callback) {
vbOnWrite prev = sim->onWrite;
sim->onWrite = callback;
return prev;
}
/* Determine the size of a simulation instance */
VBAPI size_t vbSizeOf() {
return sizeof (VB);
}
/* Specify a simulation's userdata pointer */
VBAPI void* vbSetUserData(VB *sim, void *tag) {
void *prev = sim->tag;
sim->tag = tag;
return prev;
}
/* Write a value to the memory bus */
VBAPI int32_t vbWrite(VB *sim, uint32_t address, int type, int32_t value) {
if (type < 0 || type > 4)
return 0;
busWrite(sim, address, type, value, 1);
return vbRead(sim, address, type);
}