first draft; needs tests

1 files changed, 258 insertions, 0 deletions

diff --git a/src/core.c b/src/core.c
new file mode 100644
index 0000000..c29fe96
--- /dev/null
+++ b/src/core.c
@@ -0,0 +1,258 @@
+#include "core.h"
+
+#include <stdint.h>
+
+#define MSP430_SR_C (1 << 0)
+#define MSP430_SR_Z (1 << 1)
+#define MSP430_SR_N (1 << 2)
+#define MSP430_SR_V (1 << 8)
+
+// r0 = pc
+// r1 = sp
+// r2 = sr
+
+static int msp430_do_cycle_jump(msp430_t *state, uint16_t opcode);
+int msp430_do_cycle_single_operand(msp430_t *state, uint16_t opcode);
+int msp430_do_cycle_dual_operand(msp430_t *state, uint16_t opcode);
+int msp430_do_cycle_single_operand_byte(msp430_t *state, uint16_t opcode);
+int msp430_do_cycle_dual_operand_byte(msp430_t *state, uint16_t opcode);
+
+uint16_t *msp430_do_cycle_get_single_operand(msp430_t *state, uint16_t opcode);
+uint16_t *msp430_do_cycle_get_source_operand(msp430_t *state, uint16_t opcode);
+uint16_t *msp430_do_cycle_get_dest_operand(msp430_t *state, uint16_t opcode);
+
+static inline int msp430_get_opcode_bw(uint16_t opcode);
+
+void msp430_init_state(msp430_t *state, void *mem)
+{
+	for (int i = 0; i < 16; ++i)
+		state->reg[i] = 0;
+	state->mem = mem;
+}
+
+int msp430_do_cycle(msp430_t *state)
+{
+	uint16_t pc = state->reg[0];
+	uint16_t opcode = *((uint16_t *)(state->mem + pc));
+
+	// Check for program end...
+	if (opcode == 0x4130 && state->reg[1] == 0)
+		return 1;
+
+	state->reg[0] = pc + 2;
+
+	int ret;
+	if ((opcode & 0xE000) == 0x2000) {
+		ret = msp430_do_cycle_jump(state, opcode);
+	} else {
+		int bw = msp430_get_opcode_bw(opcode);
+		if (bw == 0) {
+			if ((opcode & 0xFC00) == 0x1000)
+				ret = msp430_do_cycle_single_operand(state, opcode);
+			else
+				ret = msp430_do_cycle_dual_operand(state, opcode);
+		} else {
+			if ((opcode & 0xFC00) == 0x1000)
+				ret = msp430_do_cycle_single_operand_byte(state, opcode);
+			else
+				ret = msp430_do_cycle_dual_operand_byte(state, opcode);
+		}
+	}
+
+	return ret;
+}
+
+static void msp430_jump_to_offset(msp430_t *state, uint16_t opcode)
+{
+	uint16_t addr = opcode & 0x3FF;
+	if (addr & (1 << 9))
+		addr |= 0xFC00;
+	int16_t saddr = (int16_t)addr * 2;
+	state->reg[0] += saddr;
+}
+
+int msp430_do_cycle_jump(msp430_t *state, uint16_t opcode)
+{
+	// PC to become PC + ((opcode & 0x3FF) << 1)
+	switch ((opcode & 0x01C0) >> 10) {
+	case 0:
+		// JNE/JZ
+		if ((state->reg[2] & MSP430_SR_Z) == 0)
+			msp430_jump_to_offset(state, opcode);
+		break;
+	case 1:
+		// JEQ/JZ
+		if ((state->reg[2] & MSP430_SR_Z) == MSP430_SR_Z)
+			msp430_jump_to_offset(state, opcode);
+		break;
+	case 2:
+		// JNC/JLO
+		if ((state->reg[2] & MSP430_SR_C) == 0)
+			msp430_jump_to_offset(state, opcode);
+		break;
+	case 3:
+		// JC/JHS
+		if ((state->reg[2] & MSP430_SR_C) == MSP430_SR_C)
+			msp430_jump_to_offset(state, opcode);
+		break;
+	case 4:
+		// JN
+		if ((state->reg[2] & MSP430_SR_N) == MSP430_SR_N)
+			msp430_jump_to_offset(state, opcode);
+		break;
+	case 5: {
+		// JGE
+		uint16_t flags = state->reg[2] & (MSP430_SR_N | MSP430_SR_V);
+		if (flags == 0 || flags == (MSP430_SR_N | MSP430_SR_V))
+			msp430_jump_to_offset(state, opcode);
+		break; }
+	case 6: {
+		// JL
+		uint16_t flags = state->reg[2] & (MSP430_SR_N | MSP430_SR_V);
+		if (flags == MSP430_SR_N || flags == MSP430_SR_V)
+			msp430_jump_to_offset(state, opcode);
+		break; }
+	case 7:
+		// JMP
+		msp430_jump_to_offset(state, opcode);
+		break;
+	default:
+		return -1;
+	}
+
+	return 0;
+}
+
+uint16_t *msp430_do_cycle_get_operand(msp430_t *state, int AS, int BW, int SOURCE)
+{
+	static uint16_t constants[6] = {
+		0, 1, 2, -1, 4, 8
+	};
+
+	if (SOURCE == 0) {
+		if (AS == 1) {
+			// Operand at PC + X
+			// X = word after PC
+			uint16_t offset = *((uint16_t *)(state->mem + state->reg[0]));
+			uint16_t *ret = (uint16_t *)(state->mem + state->reg[0] + offset);
+			state->reg[0] += 2;
+			return ret;
+		} else if (AS == 3) {
+			// Operand is X
+			uint16_t *ret = (uint16_t *)(state->mem + state->reg[0]);
+			state->reg[0] += 2;
+			return ret;
+		}
+	}
+
+	if (SOURCE == 2) {
+		switch (AS) {
+		case 0:
+			// R2
+			return &state->reg[2];
+			break;
+		case 1: {
+			// Operand at X
+			uint16_t offset = *((uint16_t *)(state->mem + state->reg[0]));
+			uint16_t *ret = (uint16_t *)(state->mem + offset);
+			state->reg[0] += 2;
+			return ret;
+			break; }
+		case 2:
+			return &constants[4];
+			break;
+		case 3:
+			return &constants[5];
+			break;
+		}
+	} else if (SOURCE == 3) {
+		// Constants
+		return &constants[AS];
+	} else {
+		switch (AS) {
+		case 0:
+			// Register
+			return &state->reg[SOURCE];
+			break;
+		case 1: {
+			// Operand at Rn + X
+			uint16_t offset = *((uint16_t *)(state->mem + state->reg[0]));
+			uint16_t *ret = (uint16_t *)(state->mem + state->reg[SOURCE] + offset);
+			state->reg[0] += 2;
+			return ret;
+			break; }
+		case 2:
+			// Operand at Rn
+			return (uint16_t *)(state->mem + state->reg[SOURCE]);
+			break;
+		case 3: {
+			// Operand at Rn, increment Rn
+			uint16_t *ret = (uint16_t *)(state->mem + state->reg[SOURCE]);
+			state->reg[SOURCE] += BW ? 1 : 2;
+			return ret;
+			break; }
+		}
+	}
+
+	return 0; // Failed...
+}
+
+inline int msp430_get_opcode_bw(uint16_t opcode)
+{
+	return opcode & (1 << 6);
+}
+
+uint16_t *msp430_do_cycle_get_single_operand(msp430_t *state, uint16_t opcode)
+{
+	return msp430_do_cycle_get_operand(state,
+		/* AS */     (opcode & 0x30) >> 4,
+		/* BW */     msp430_get_opcode_bw(opcode),
+		/* SOURCE */ (opcode & 0xF));
+}
+
+uint16_t *msp430_do_cycle_get_source_operand(msp430_t *state, uint16_t opcode)
+{
+	return msp430_do_cycle_get_operand(state,
+		/* AS */     (opcode & 0x30) >> 4,
+		/* BW */     msp430_get_opcode_bw(opcode),
+		/* SOURCE */ (opcode & 0xF00) >> 8);
+}
+uint16_t *msp430_do_cycle_get_dest_operand(msp430_t *state, uint16_t opcode)
+{
+	int AD = opcode & 0x80;
+	int DEST = opcode & 0xF;
+
+	if (AD == 0) {
+		// Byte operation? Clear MSB.
+		if (msp430_get_opcode_bw(opcode) == 0) {
+			return &state->reg[DEST];
+		} else {
+			uint16_t *ret = &state->reg[DEST];
+			*ret &= 0xFF;
+			return ret;
+		}
+	} else {
+		if (DEST == 0) {
+			// dest at PC + X
+			uint16_t offset = *((uint16_t *)(state->mem + state->reg[0]));
+			uint16_t *ret = (uint16_t *)(state->mem + state->reg[0] + offset);
+			state->reg[0] += 2;
+			return ret;
+		} else if (DEST == 2) {
+			// dest at X
+			uint16_t offset = *((uint16_t *)(state->mem + state->reg[0]));
+			uint16_t *ret = (uint16_t *)(state->mem + offset);
+			state->reg[0] += 2;
+			return ret;
+		} else {
+			// dest at Rn + X
+			uint16_t offset = *((uint16_t *)(state->mem + state->reg[0]));
+			uint16_t *ret = (uint16_t *)(state->mem + state->reg[DEST] + offset);
+			state->reg[0] += 2;
+			return ret;
+		}
+	}
+
+	return 0;
+}
+