mirror of
https://github.com/libretro/oberon-risc-emu.git
synced 2024-12-04 23:16:43 +00:00
425 lines
10 KiB
C
425 lines
10 KiB
C
#include <stdint.h>
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#include <stdbool.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdio.h>
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#include "risc.h"
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#include "risc-sd.h"
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#define MemSize 0x100000
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#define MemWords (MemSize / 4)
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#define ROMStart 0x0FE000
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#define ROMWords 512
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#define DisplayStart 0x0E7F00
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#define DIsplayEnd (DisplayStart + 1024*768/8)
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#define RegStart 0x0FFFC0
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struct RISC {
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uint32_t PC;
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uint32_t R[16];
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uint32_t H;
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bool Z, N, C, V;
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uint32_t progress;
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uint32_t current_tick;
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uint32_t mouse;
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uint8_t key_buf[16];
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uint32_t key_cnt;
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uint32_t leds;
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uint32_t spi_selected;
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struct Disk *sd_card;
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uint32_t RAM[MemWords];
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uint32_t ROM[ROMWords];
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};
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enum {
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MOV, LSL, ASR, ROR,
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AND, ANN, IOR, XOR,
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ADD, SUB, MUL, DIV,
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FAD, FSB, FML, FDV,
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};
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static void risc_single_step(struct RISC *risc);
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static uint32_t risc_load_word(struct RISC *risc, uint32_t address);
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static uint8_t risc_load_byte(struct RISC *risc, uint32_t address);
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static void risc_store_word(struct RISC *risc, uint32_t address, uint32_t value);
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static void risc_store_byte(struct RISC *risc, uint32_t address, uint8_t value);
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static uint32_t risc_load_register(struct RISC *risc, uint32_t address);
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static void risc_store_register(struct RISC *risc, uint32_t address, uint32_t value);
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// Not very portable :)
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union float_cvt { float f; uint32_t u; };
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static float u2f(uint32_t u) { return (union float_cvt){ .u = u }.f; }
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static float f2u(float f) { return (union float_cvt){ .f = f }.u; }
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static const uint32_t bootloader[ROMWords] = {
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#include "risc-boot.inc"
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};
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struct RISC *risc_new(const char *disk_file) {
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struct RISC *risc = calloc(1, sizeof(*risc));
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memcpy(risc->ROM, bootloader, sizeof(risc->ROM));
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risc->PC = ROMStart/4;
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if (disk_file) {
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risc->sd_card = disk_new(disk_file);
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}
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return risc;
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}
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void risc_free(struct RISC *risc) {
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disk_free(risc->sd_card);
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free(risc);
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}
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void risc_run(struct RISC *risc, int cycles) {
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risc->progress = 20;
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// The progress value is used to detect that the RISC cpu is busy
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// waiting on the millisecond counter or on the keyboard ready
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// bit. In that case it's better to just pause emulation until the
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// next frame.
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for (int i = 0; i < cycles && risc->progress; i++) {
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risc_single_step(risc);
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}
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}
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static void risc_single_step(struct RISC *risc) {
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uint32_t ir;
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if (risc->PC < ROMStart/4) {
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ir = risc->RAM[risc->PC];
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} else {
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ir = risc->ROM[risc->PC - ROMStart/4];
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}
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risc->PC++;
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const uint32_t pbit = 0x80000000;
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const uint32_t qbit = 0x40000000;
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const uint32_t ubit = 0x20000000;
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const uint32_t vbit = 0x10000000;
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if ((ir & pbit) == 0) {
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// Register instructions
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uint32_t a = (ir & 0x0F000000) >> 24;
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uint32_t b = (ir & 0x00F00000) >> 20;
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uint32_t op = (ir & 0x000F0000) >> 16;
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uint32_t im = ir & 0x0000FFFF;
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uint32_t c = ir & 0x0000000F;
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uint32_t a_val, b_val, c_val;
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b_val = risc->R[b];
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if ((ir & qbit) == 0) {
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c_val = risc->R[c];
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} else if ((ir & vbit) == 0) {
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c_val = im;
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} else {
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c_val = 0xFFFF0000 | im;
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}
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switch (op) {
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case MOV: {
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if ((ir & ubit) == 0) {
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a_val = c_val;
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} else if ((ir & qbit) != 0) {
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a_val = c_val << 16;
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} else if ((ir & vbit) != 0) {
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a_val = 0xD0 | // FIXME ???
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(risc->N * 0x80000000) |
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(risc->Z * 0x40000000) |
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(risc->C * 0x20000000) |
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(risc->V * 0x10000000);
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} else {
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a_val = risc->H;
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}
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break;
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}
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case LSL: {
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a_val = b_val << (c_val & 31);
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break;
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}
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case ASR: {
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a_val = ((int32_t) b_val) >> (c_val & 31);
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break;
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}
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case ROR: {
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a_val = (b_val >> (c_val & 31)) | (b_val << (-c_val & 31));
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break;
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}
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case AND: {
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a_val = b_val & c_val;
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break;
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}
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case ANN: {
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a_val = b_val & ~c_val;
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break;
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}
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case IOR: {
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a_val = b_val | c_val;
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break;
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}
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case XOR: {
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a_val = b_val ^ c_val;
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break;
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}
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case ADD: {
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uint64_t tmp = (uint64_t)b_val + c_val;
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if ((ir & ubit) & risc->C) {
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tmp++;
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}
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a_val = (uint32_t) tmp;
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risc->C = tmp >> 32;
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risc->V = (~(b_val ^ c_val) & (a_val ^ b_val)) >> 31;
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break;
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}
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case SUB: {
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uint64_t tmp = (uint64_t)b_val - c_val;
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if ((ir & ubit) & risc->C) {
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tmp--;
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}
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a_val = (uint32_t)tmp;
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risc->C = tmp >> 32;
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risc->V = ((b_val ^ c_val) & (a_val ^ b_val)) >> 31;
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break;
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}
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case MUL: {
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uint64_t tmp;
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if ((ir & ubit)) {
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tmp = (int64_t)(int32_t)b_val * (int64_t)(int32_t)c_val;
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} else {
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tmp = (uint64_t)b_val * (uint64_t)c_val;
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}
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a_val = (uint32_t)tmp;
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risc->H = tmp >> 32;
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break;
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}
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case DIV: {
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a_val = (int32_t)b_val / (int32_t)c_val;
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risc->H = (int32_t)b_val % (int32_t)c_val;
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break;
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}
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case FAD: {
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a_val = f2u(u2f(b_val) + u2f(c_val));
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break;
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}
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case FSB: {
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a_val = f2u(u2f(b_val) - u2f(c_val));
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break;
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}
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case FML: {
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a_val = f2u(u2f(b_val) * u2f(c_val));
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break;
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}
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case FDV: {
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a_val = f2u(u2f(b_val) / u2f(c_val));
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break;
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}
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}
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risc->R[a] = a_val;
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risc->Z = a_val == 0;
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risc->N = (int32_t)a_val < 0;
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}
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else if ((ir & qbit) == 0) {
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// Memory instructions
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uint32_t a = (ir & 0x0F000000) >> 24;
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uint32_t b = (ir & 0x00F00000) >> 20;
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uint32_t off = ir & 0x000FFFFF;
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uint32_t address = (risc->R[b] + off) % MemSize;
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if ((ir & ubit) == 0) {
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uint32_t a_val;
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if ((ir & vbit) == 0) {
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a_val = risc_load_word(risc, address);
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} else {
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a_val = risc_load_byte(risc, address);
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}
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risc->R[a] = a_val;
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risc->Z = a_val == 0;
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risc->N = (int32_t)a_val < 0;
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} else {
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if ((ir & vbit) == 0) {
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risc_store_word(risc, address, risc->R[a]);
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} else {
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risc_store_byte(risc, address, risc->R[a]);
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}
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}
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}
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else {
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// Branch instructions
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bool t;
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switch ((ir >> 24) & 15) {
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case 0: t = risc->N; break;
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case 1: t = risc->Z; break;
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case 2: t = risc->C; break;
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case 3: t = risc->V; break;
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case 4: t = risc->C || risc->Z; break;
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case 5: t = risc->N != risc->V; break;
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case 6: t = (risc->N != risc->V) || risc->Z; break;
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case 7: t = true; break;
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case 8: t = !risc->N; break;
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case 9: t = !risc->Z; break;
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case 10: t = !risc->C; break;
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case 11: t = !risc->V; break;
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case 12: t = !(risc->C || risc->Z); break;
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case 13: t = !(risc->N != risc->V); break;
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case 14: t = !((risc->N != risc->V) || risc->Z); break;
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case 15: t = false; break;
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}
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if (t) {
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if ((ir & vbit) != 0) {
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risc->R[15] = risc->PC * 4;
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}
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if ((ir & ubit) == 0) {
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uint32_t c = ir & 0x0000000F;
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risc->PC = (risc->R[c] / 4) % MemWords;
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} else {
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uint32_t off = ir & 0x00FFFFFF;
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risc->PC = (risc->PC + off) % MemWords;
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}
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}
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}
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}
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static uint32_t risc_load_word(struct RISC *risc, uint32_t address) {
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if (address < RegStart) {
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return risc->RAM[address/4];
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} else {
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return risc_load_register(risc, address);
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}
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}
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static uint8_t risc_load_byte(struct RISC *risc, uint32_t address) {
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uint32_t w = risc_load_word(risc, address);
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return w >> ((address & 3) * 8);
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}
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static void risc_store_word(struct RISC *risc, uint32_t address, uint32_t value) {
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if (address < RegStart) {
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risc->RAM[address/4] = value;
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} else {
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risc_store_register(risc, address, value);
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}
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}
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static void risc_store_byte(struct RISC *risc, uint32_t address, uint8_t value) {
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if (address < RegStart) {
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uint32_t w = risc_load_word(risc, address);
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uint32_t shift = (address & 3) * 8;
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w &= ~(0xFFu << shift);
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w |= (uint32_t)value << shift;
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risc_store_word(risc, address, w);
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}
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}
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static uint32_t risc_load_register(struct RISC *risc, uint32_t address) {
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switch (address - RegStart) {
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case 0: {
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// millisecond counter
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risc->progress--;
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return risc->current_tick;
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}
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case 4: {
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// switches
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return 0;
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}
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case 16: {
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// SPI data
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if (risc->spi_selected == 1 && risc->sd_card) {
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return disk_read(risc->sd_card);
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}
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return 255;
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}
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case 20: {
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// SPI status
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return 1;
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}
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case 24: {
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// mouse
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uint32_t mouse = risc->mouse;
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if (risc->key_cnt > 0) {
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mouse |= 0x10000000;
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} else {
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risc->progress--;
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}
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return mouse;
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}
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case 28: {
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if (risc->key_cnt > 0) {
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uint8_t scancode = risc->key_buf[0];
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risc->key_cnt--;
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memmove(&risc->key_buf[0], &risc->key_buf[1], risc->key_cnt);
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return scancode;
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}
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return 0;
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}
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default: {
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return 0;
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}
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}
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}
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static void risc_store_register(struct RISC *risc, uint32_t address, uint32_t value) {
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switch (address - RegStart) {
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case 4: {
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// LED control
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risc->leds = value;
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printf("LEDs: ");
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for (int i = 7; i >= 0; i--) {
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if (risc->leds & (1 << i)) {
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printf("%d", i);
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} else {
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printf("-");
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}
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}
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printf("\n");
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break;
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}
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case 16: {
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if (risc->spi_selected == 1 && risc->sd_card) {
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disk_write(risc->sd_card, value);
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}
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break;
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}
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case 20: {
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// SPI control
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risc->spi_selected = value & 3;
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break;
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}
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}
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}
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void risc_set_time(struct RISC *risc, uint32_t tick) {
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risc->current_tick = tick;
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}
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void risc_mouse_moved(struct RISC *risc, int mouse_x, int mouse_y) {
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if (mouse_x >= 0 && mouse_x < 1024) {
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risc->mouse = (risc->mouse & ~0x00000FFF) | mouse_x;
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}
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if (mouse_y >= 0 && mouse_y < 1024) {
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risc->mouse = (risc->mouse & ~0x00FFF000) | (mouse_y << 12);
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}
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}
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void risc_mouse_button(struct RISC *risc, int button, bool down) {
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if (button >= 1 && button < 4) {
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int bit = 1 << (27 - button);
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risc->mouse &= ~bit;
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if (down) {
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risc->mouse |= bit;
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}
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}
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}
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void risc_keyboard_input(struct RISC *risc, uint8_t *scancodes, uint32_t len) {
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if (sizeof(risc->key_buf) - risc->key_cnt >= len) {
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memmove(&risc->key_buf[risc->key_cnt], scancodes, len);
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risc->key_cnt += len;
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}
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}
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uint32_t *risc_get_framebuffer_ptr(struct RISC *risc) {
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return &risc->RAM[DisplayStart/4];
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}
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