rvemu

commit 57eaef5ec609fa7e243fca6494754866004db66b
parent e4f8168882930df9b5947a9ac146cb176c4fad53
Author: Michail Konstantinos Dimopoulos <mk@mcdim.xyz>
Date:   Mon, 23 Mar 2026 21:30:21 +0200

Added btype decoding and beq instruction

Diffstat:
M
main.c
 | 
71
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----

1 file changed, 67 insertions(+), 4 deletions(-)
diff --git a/main.c b/main.c
@@ -408,6 +408,62 @@ void exec_stype(cpu_state_t *cpu, uint32_t inst, uint8_t *mem) {
 	}
 }
 
+/*
+B-TYPE INSTRUCTION FORMAT
+31            25 24    20 19    15 14    12 11         7 6       0
++---------------+--------+--------+--------+------------+--------+
+| imm[12|10:5]  |  rs2   |  rs1   | funct3 |imm[4:1|11] | opcode |
++---------------+--------+--------+--------+------------+--------+
+opcode	 0x63	 1100010 
+*/
+void exec_btype(cpu_state_t *cpu, uint32_t inst, uint8_t *mem) {
+	printf("TYPE B\n");
+	stype_t b;
+
+	uint32_t imm_10_5 = (inst >> 25) & 63;
+	uint32_t imm_11 = (inst >> 7) & 1;
+	uint32_t imm_4_1 = (inst >> 8) & 15;
+	uint32_t imm_12 = (inst >> 31) & 1;
+	b.imm = 0 | (imm_4_1 << 1) | (imm_10_5 << 5) | (imm_11 << 11) | (imm_12 << 12);
+
+	b.funct3 = (inst >> 12) & 7;
+	b.rs1 = (inst >> 15) & 31;
+	b.rs2 = (inst >> 20) & 31;
+
+	printf("\nimm:%x\n", b.imm);
+
+	/**print**/
+	printf("imm       rs2   rs1   f3  imm      opcode\n");
+	printf("[12|10:5]                 [4:1|11]\n");
+	print_binless(imm_12, 1);
+	print_binless(imm_10_5, 6);
+	printf("   ");
+	print_binless(b.rs2, 5);
+	printf(" ");
+	print_binless(b.rs1, 5);
+	printf(" ");
+	print_binless(b.funct3, 3);
+	printf(" ");
+	print_binless(imm_4_1, 4);
+	print_binless(imm_11, 1);
+	printf("\n");
+	/*********/
+
+	printf("PC:%d\n", cpu->pc);
+	switch (b.funct3) {
+	case 0x0:
+		if (cpu->x[b.rs1] == cpu->x[b.rs2]) {
+			if (b.imm >= MEMSIZE) {
+				fprintf(stderr, "Illegal address\n");
+				return;
+			}
+			cpu->pc += b.imm;
+		}
+	}
+
+	printf("PC:%d\n", cpu->pc);
+}
+
 int main() {
 
 	/* function pointer dispatch */
@@ -418,10 +474,8 @@ int main() {
 	opcode_table[0x13] = exec_itype;
 	opcode_table[0x03] = exec_ltype;
 	opcode_table[0x23] = exec_stype;
+	opcode_table[0x63] = exec_btype;
 	/*opcode_table[0x13] = exec_rtype_imm;
-	opcode_table[0x03] = exec_load;
-	opcode_table[0x23] = exec_store;
-	opcode_table[0x63] = exec_branch;
 	opcode_table[0x73] = exec_system;*/
 
 
@@ -494,6 +548,11 @@ int main() {
 	//	0000000 00000 00000 010 00011 0100011
 	inst = 0x21A3; /* STORE rs2 contents to mem 0x03, FAIL (word)*/
 
+	//	imm      rs2   rs1   f3  imm      opcode
+	//      [12|10:5]                [4:1|11]
+	//	0000000  00000 00000 000 00010    1100011
+	inst = 0x163; /* branch to 2 if rs1 == rs2*/
+
 	print_bin32(inst);
 	printf("\n");
 
@@ -504,11 +563,15 @@ int main() {
 	printf("\n");
 
 	exec_fn fn = opcode_table[opcode];
-	cpu_state_t cpu;
+
 	/* init cpu state */
+	cpu_state_t cpu;
 	for (int i=0; i<32; i++) {
 		cpu.x[i] = 0;
 	}
+	cpu.pc = 0;
+	/* */
+
 	cpu.x[1] = 51;
 	cpu.x[2] = 00;