rvemu

commit 4446e4fbe7569a37b01c06a28e26ef64c45c6e8c
Author: Michail Konstantinos Dimopoulos <mk@mcdim.xyz>
Date:   Mon, 16 Mar 2026 23:49:55 +0200

Initial commit

Diffstat:
A
Makefile
 | 
2
++
A
config.h
 | 
2
++
A
main.c
 | 
167
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

3 files changed, 171 insertions(+), 0 deletions(-)
diff --git a/Makefile b/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc main.c
diff --git a/config.h b/config.h
@@ -0,0 +1,2 @@
+#define MEM_SIZE (32 * 1024 * 1024)
+
diff --git a/main.c b/main.c
@@ -0,0 +1,167 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct {
+	uint32_t x[32];  /* general purpose registers */
+	uint32_t pc;
+} cpu_state_t;
+
+typedef struct {
+	uint8_t opcode;
+	uint8_t rd, rs1, rs2;
+	uint8_t funct3, funct7;
+} rtype_t;
+
+void print_bin16(uint16_t x) {
+	for (int i = 15; i >= 0; i--) {
+		putchar((x >> i) & 1 ? '1' : '0');
+		/*if (i % 4 == 0) putchar(' '); grouping */
+	}
+}
+
+void print_bin32(uint32_t x) {
+	for (int i = 31; i >= 0; i--) {
+		putchar((x >> i) & 1 ? '1' : '0');
+	}
+}
+
+void print_binless(uint32_t x, int a) {
+	for (int i = a-1; i >= 0; i--) {
+		putchar((x >> i) & 1 ? '1' : '0');
+	}
+}
+
+/*
+R-TYPE INSTRUCTION DECODING
+31         25 24    20 19    15 14    12 11      7 6      0
++------------+--------+--------+--------+---------+--------+
+|   funct7   |  rs2   |  rs1   | funct3 |   rd    | opcode |
++------------+--------+--------+--------+---------+--------+
+opcode	 0x33	 0110011 
+*/
+void exec_op(cpu_state_t *cpu, uint32_t inst) {
+	printf("TYPE R\n");
+	rtype_t r;
+	r.rd = (inst >> 7) & 31;
+	r.funct3 = (inst >> 12) & 7;
+	r.rs1 = (inst >> 15) & 31;
+	r.rs2 = (inst >> 20) & 31;
+	r.funct7 = (inst >> 25) & 127;
+
+	/* print */
+	printf("f7      rs2   rs1   f3  rd    opcode\n");
+	print_binless(r.funct7, 7);
+	printf(" ");
+	print_binless(r.rs2, 5);
+	printf(" ");
+	print_binless(r.rs1, 5);
+	printf(" ");
+	print_binless(r.funct3, 3);
+	printf(" ");
+	print_binless(r.rd, 5);
+	printf("\n");
+
+	/* */
+
+	switch(r.funct3) {
+	case 0x0:
+		printf("HI\n\n");
+		switch(r.funct7) {
+		case 0x00:
+			printf("ADD\n");
+			printf("rs1:%d\nrs2:%d\nrd:%d\n",cpu->x[r.rs1],cpu->x[r.rs2],cpu->x[r.rd]);
+				
+			int x = cpu->x[r.rs1]+cpu->x[r.rs2];
+
+			printf("%d\n", x);
+
+			if (r.rd != 0) {
+				cpu->x[r.rd] = x;
+			}
+
+			printf("rd:%d\n", cpu->x[r.rd]);
+
+			break;
+		case 0x20:
+			printf("SUB\n");
+			printf("rs1:%d\nrs2:%d\nrd:%d\n",cpu->x[r.rs1],cpu->x[r.rs2],cpu->x[r.rd]);
+
+			x = cpu->x[r.rs1]-cpu->x[r.rs2];
+
+			if (r.rd != 0) {
+				cpu->x[r.rd] = x;
+			}
+
+			printf("rd:%d\n", cpu->x[r.rd]);
+			break;
+		}
+		break;
+	case 0x4:
+		printf("XOR\n");
+		break;
+	case 0x6:
+		printf("OR\n");
+		break;
+	case 0x7:
+		printf("AND\n");
+		printf("rs1:%d\nrs2:%d\nrd:%d",cpu->x[r.rs1],cpu->x[r.rs2],cpu->x[r.rd]);
+		
+		int x = r.rs1&r.rs2;
+		printf("%d\n", x);
+		break;
+	}
+}
+
+int main() {
+
+	/* function pointer dispatch */
+	typedef void (*exec_fn)(cpu_state_t *, uint32_t inst);
+	static exec_fn opcode_table[128];
+	opcode_table[0x33] = exec_op;
+	/*opcode_table[0x13] = exec_op_imm;
+	opcode_table[0x03] = exec_load;
+	opcode_table[0x23] = exec_store;
+	opcode_table[0x63] = exec_branch;
+	opcode_table[0x73] = exec_system;*/
+
+
+	/*0000000111110000011100000110011*/
+	//uint32_t inst = 0x01F07033;
+	/*0000000111110000000000000110011*/
+	uint32_t inst = 0x01F00033;
+
+	//	f7      rs2   rs1   f3  rd    opcode
+	//	0000000 00001 00010 000 00000 0110011
+	inst = 0x00110033;
+
+	//	f7      rs2   rs1   f3  rd    opcode
+	//	0100000 00001 00010 000 00011 0110011
+	//inst = 0x401101B3;
+
+	print_bin32(inst);
+	printf("\n");
+
+	/* decode instruction */
+	uint16_t opcode = inst & 127;
+	printf("opcode:");
+	printf("\n");
+	print_bin16(opcode);
+	printf("\n");
+
+	exec_fn fn = opcode_table[opcode];
+	cpu_state_t cpu;
+	cpu.x[1] = 5;
+	cpu.x[2] = 14;
+	
+
+	if (!fn) {
+		//illegal(NULL, inst);
+		fprintf(stderr, "Illegal opcode\n");
+		return EXIT_FAILURE;
+	}
+
+	fn(&cpu,inst);
+
+	return 0;
+}