1 | ; Project name : Assembly Library
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2 | ; Description : Macros for preventing CGA snow.
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3 | %ifndef CGASNOW_INC
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4 | %define CGASNOW_INC
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5 |
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6 | ;--------------------------------------------------------------------
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7 | ; CALL_WAIT_FOR_RETRACE_IF_NECESSARY_THEN
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8 | ; JMP_WAIT_FOR_RETRACE_IF_NECESSARY_THEN
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9 | ; Parameters:
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10 | ; %1: Instruction that accesses CGA memory
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11 | ; AL: Character to output
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12 | ; AH: Attribute to output (stosw only)
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13 | ; DS: BDA segment (zero)
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14 | ; ES:SI: Ptr to video memory where to read from (if %1 reads)
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15 | ; ES:DI: Ptr to video memory where to output (if %1 writes)
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16 | ; Returns:
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17 | ; SI, DI: Updated according to instruction
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18 | ; Corrupts registers:
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19 | ; AX, DX
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20 | ;--------------------------------------------------------------------
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21 | %macro CALL_WAIT_FOR_RETRACE_IF_NECESSARY_THEN 1
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22 | %ifdef ELIMINATE_CGA_SNOW
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23 | %ifidn %1, stosb
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24 | call CgaSnow_Stosb
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25 | %elifidn %1, stosw
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26 | call CgaSnow_Stosw
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27 | %elifidn %1, rep movsb
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28 | call CgaSnow_RepMovsb
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29 | %else
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30 | %error "Invalid instruction passed to CALL_WAIT_FOR_RETRACE_IF_NECESSARY_THEN"
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31 | %endif
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32 | %else ; No CGA snow prevention
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33 | %ifidn %1, rep movsb
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34 | eSEG_STR rep, es, movsb
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35 | %else
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36 | %1 ; Single instruction
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37 | %endif
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38 | %endif
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39 | %endmacro
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40 |
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41 | %macro JMP_WAIT_FOR_RETRACE_IF_NECESSARY_THEN 1
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42 | %ifdef ELIMINATE_CGA_SNOW
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43 | %ifidn %1, stosb
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44 | jmp CgaSnow_Stosb
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45 | %elifidn %1, stosw
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46 | jmp CgaSnow_Stosw
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47 | %elifidn %1, rep movsb
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48 | jmp CgaSnow_RepMovsb
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49 | %else
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50 | %error "Invalid instruction passed to JMP_WAIT_FOR_RETRACE_IF_NECESSARY_THEN"
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51 | %endif
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52 | %else ; No CGA snow prevention
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53 | %ifidn %1, rep movsb
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54 | eSEG_STR rep, es, movsb
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55 | ret
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56 | %else
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57 | %1 ; Single instruction
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58 | ret
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59 | %endif
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60 | %endif
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61 | %endmacro
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62 |
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63 |
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64 | ;--------------------------------------------------------------------
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65 | ; WAIT_UNTIL_SAFE_CGA_WRITE
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66 | ; Parameters:
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67 | ; DX: CGA Status Register Address (3DAh)
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68 | ; Returns:
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69 | ; Nothing
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70 | ; Corrupts registers:
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71 | ; AL
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72 | ;--------------------------------------------------------------------
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73 | %macro WAIT_UNTIL_SAFE_CGA_WRITE 0
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74 | %%WaitUntilNotInRetrace:
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75 | in al, dx
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76 | shr al, 1 ; 1 = Bit 0: A 1 indicates that regen-buffer memory access can be
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77 | ; made without interfering with the display. (H or V retrace)
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78 | jc SHORT %%WaitUntilNotInRetrace
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79 | %%WaitUntilNextRetraceStarts:
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80 | in al, dx
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81 | shr al, 1
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82 | jnc SHORT %%WaitUntilNextRetraceStarts
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83 | %endmacro
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84 |
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85 |
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86 | %endif ; CGASNOW_INC
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