Initial work on M68K instruction decoding

1 files changed, 92 insertions, 0 deletions

diff --git a/68kinst.c b/68kinst.c
new file mode 100644
index 0000000..dcb9501
--- /dev/null
+++ b/68kinst.c
@@ -0,0 +1,92 @@
+#include "68kinst.h"
+
+void m68k_decode_op(uint16_t op, m68k_op_info *dst)
+{
+	uint8_t mode = (op >> 3) & 0x7;
+	uint8_t reg = op & 0x7;
+	dst->addr_mode = mode;
+	switch(mode)
+	{
+	case MODE_REG:
+	case MODE_AREG:
+		dst->params.regs.pri = reg;
+		break;
+	case MODE_
+	}
+}
+
+uint16_t * m68K_decode(uint16_t * istream, m68kinst * decoded)
+{
+	uint8_t optype = *istream >> 12;
+	uint8_t size;
+	uint8_t immed;
+	switch(optype)
+	{
+	case BIT_MOVEP_IMMED:
+		//TODO: Implement me
+		break;
+	case MOVE_BYTE:
+	case MOVE_LONG:
+	case MOVE_WORD:
+		decoded->op = M68K_MOVE;
+		decoded->extra.size = optype == MOVE_BYTE ? OPSIZE_BYTE : (optype == MOVE_WORD ? OPSIZE_WORD : OPSIZE_LONG);
+		m68k_decode_op(*istream, &(decoded->src));
+		m68k_decode_op(((*istream >> 9) & 0x7) | , &(decoded->dst));
+		break;
+	case MISC:
+		//TODO: Implement me
+		break;
+	case QUICK_ARITH_LOOP:
+		size = (*istream >> 6) & 3;
+		if (size == 0x3) {
+			//DBcc, TRAPcc or Scc
+			decoded->extra.cond = (*istream >> 0x8) & 0xF;
+			switch ((*istream >> 3) & 0x7)
+			{
+			case 1: //DBcc
+				decoded->op = M68K_DBCC;
+				decoded->dst.addr_mode = MODE_REG;
+				decoded->dst.regs.pri = *istream & 0x7;
+				break;
+			case 7: //TRAPcc
+				decoded->op = M68K_TRAPCC;
+				decoded->src.addr_mode = MODE_PC_INDIRECT_ABS_IMMED;
+				decoded->src.regs.pri = MODE_IMMEDIATE;
+				//TODO: Figure out what to do with OPMODE and optional extention words
+				break;
+			default: //Scc
+				decoded->op = M68K_SCC;
+				M68k_decode_op(*istream, &(decoded->dst));
+				break;
+			}
+		} else {
+			//ADDQ, SUBQ
+			decoded->variant = VAR_QUICK;
+			decoded->extra.size = size;
+			decoded->src.addr_mode = MODE_PC_INDIRECT_ABS_IMMED;
+			decoded->src.regs.pri = MODE_IMMEDIATE;
+			immed = (*istream >> 9) & 0x7
+			if (!immed) {
+				immed = 8;
+			}
+			switch (size)
+			{
+			case OPSIZE_BYTE;
+				decoded->src.params.u8 = immed;
+				break;
+			case OPSIZE_WORD:
+				decoded->src.params.u16 = immed;
+				break;
+			case OPSIZE_LONG:
+				decoded->src.params.u38 = immed;
+				break;
+			}
+			if (*istream & 0x10) {
+				decoded->op = M68K_SUB;
+			} else {
+				decoded->op = M68K_ADD;
+			}
+		}
+		break;
+	}
+}