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annotate 68kinst.c @ 0:2432d177e1ac

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Initial work on M68K instruction decoding
author Mike Pavone <pavone@retrodev.com>
date Mon, 29 Oct 2012 01:18:38 -0700
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children 5df303bf72e6
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2432d177e1ac Initial work on M68K instruction decoding
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1 #include "68kinst.h"
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2
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3 void m68k_decode_op(uint16_t op, m68k_op_info *dst)
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4 {
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5 uint8_t mode = (op >> 3) & 0x7;
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6 uint8_t reg = op & 0x7;
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7 dst->addr_mode = mode;
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8 switch(mode)
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9 {
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10 case MODE_REG:
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11 case MODE_AREG:
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12 dst->params.regs.pri = reg;
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13 break;
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14 case MODE_
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15 }
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16 }
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17
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18 uint16_t * m68K_decode(uint16_t * istream, m68kinst * decoded)
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19 {
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20 uint8_t optype = *istream >> 12;
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21 uint8_t size;
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22 uint8_t immed;
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23 switch(optype)
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24 {
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25 case BIT_MOVEP_IMMED:
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26 //TODO: Implement me
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27 break;
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28 case MOVE_BYTE:
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29 case MOVE_LONG:
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30 case MOVE_WORD:
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31 decoded->op = M68K_MOVE;
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32 decoded->extra.size = optype == MOVE_BYTE ? OPSIZE_BYTE : (optype == MOVE_WORD ? OPSIZE_WORD : OPSIZE_LONG);
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33 m68k_decode_op(*istream, &(decoded->src));
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34 m68k_decode_op(((*istream >> 9) & 0x7) | , &(decoded->dst));
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35 break;
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36 case MISC:
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37 //TODO: Implement me
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38 break;
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39 case QUICK_ARITH_LOOP:
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40 size = (*istream >> 6) & 3;
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41 if (size == 0x3) {
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42 //DBcc, TRAPcc or Scc
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43 decoded->extra.cond = (*istream >> 0x8) & 0xF;
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44 switch ((*istream >> 3) & 0x7)
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45 {
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46 case 1: //DBcc
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47 decoded->op = M68K_DBCC;
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48 decoded->dst.addr_mode = MODE_REG;
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49 decoded->dst.regs.pri = *istream & 0x7;
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50 break;
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51 case 7: //TRAPcc
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52 decoded->op = M68K_TRAPCC;
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53 decoded->src.addr_mode = MODE_PC_INDIRECT_ABS_IMMED;
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54 decoded->src.regs.pri = MODE_IMMEDIATE;
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55 //TODO: Figure out what to do with OPMODE and optional extention words
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56 break;
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57 default: //Scc
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58 decoded->op = M68K_SCC;
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59 M68k_decode_op(*istream, &(decoded->dst));
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60 break;
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61 }
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62 } else {
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63 //ADDQ, SUBQ
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64 decoded->variant = VAR_QUICK;
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65 decoded->extra.size = size;
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66 decoded->src.addr_mode = MODE_PC_INDIRECT_ABS_IMMED;
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67 decoded->src.regs.pri = MODE_IMMEDIATE;
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68 immed = (*istream >> 9) & 0x7
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69 if (!immed) {
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70 immed = 8;
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71 }
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72 switch (size)
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73 {
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74 case OPSIZE_BYTE;
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75 decoded->src.params.u8 = immed;
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76 break;
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77 case OPSIZE_WORD:
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78 decoded->src.params.u16 = immed;
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79 break;
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80 case OPSIZE_LONG:
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81 decoded->src.params.u38 = immed;
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82 break;
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83 }
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84 if (*istream & 0x10) {
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85 decoded->op = M68K_SUB;
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86 } else {
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87 decoded->op = M68K_ADD;
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88 }
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89 }
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90 break;
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91 }
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92 }