| 1 | ; File name : CgaSnow.inc
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| 2 | ; Project name : AssemblyLibrary
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| 3 | ; Created date : 8.10.2010
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| 4 | ; Last update : 8.10.2010
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| 5 | ; Author : Tomi Tilli
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| 6 | ; Description : Macros for preventing CGA snow.
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| 7 | %ifndef CGASNOW_INC
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| 8 | %define CGASNOW_INC
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| 9 |
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| 10 | ;--------------------------------------------------------------------
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| 11 | ; WAIT_RETRACE_IF_NECESSARY_THEN
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| 12 | ; Parameters:
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| 13 | ; %1: Instruction that accessed CGA memory
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| 14 | ; AL: Character to output
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| 15 | ; AH: Attribute to output (stosw only)
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| 16 | ; DS: BDA segment (zero)
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| 17 | ; ES:SI: Ptr to video memory where to read from (if %1 reads)
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| 18 | ; ES:DI: Ptr to video memory where to output (if %1 writes)
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| 19 | ; Returns:
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| 20 | ; SI, DI: Updated according to instruction
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| 21 | ; Corrupts registers:
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| 22 | ; AX, DX
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| 23 | ;--------------------------------------------------------------------
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| 24 | %macro WAIT_RETRACE_IF_NECESSARY_THEN 1
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| 25 | %ifdef ELIMINATE_CGA_SNOW
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| 26 | %ifidn %1, stosb
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| 27 | call CgaSnow_StosbWithoutCgaSnow
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| 28 | %elifidn %1, stosw
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| 29 | call CgaSnow_StoswWithoutCgaSnow
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| 30 | %elifidn %1, scasb
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| 31 | call CgaSnow_ScasbWithoutCgaSnow
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| 32 | %elifidn %1, rep movsb
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| 33 | call CgaSnow_RepMovsbWithoutCgaSnow
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| 34 | %else
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| 35 | %error "Invalid instruction passed to WAIT_RETRACE_IF_NECESSARY_THEN"
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| 36 | %endif
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| 37 | %else ; No CGA snow prevention
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| 38 | %ifidn %1, rep movsb
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| 39 | eSEG_STR rep, es, movsb
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| 40 | %else
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| 41 | %1 ; Single instruction
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| 42 | %endif
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| 43 | %endif
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| 44 | %endmacro
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| 45 |
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| 46 |
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| 47 | ;--------------------------------------------------------------------
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| 48 | ; WAIT_UNTIL_SAFE_CGA_WRITE
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| 49 | ; Parameters:
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| 50 | ; DX: CGA Status Register Address (3DAh)
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| 51 | ; Returns:
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| 52 | ; Nothing
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| 53 | ; Corrupts registers:
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| 54 | ; AL
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| 55 | ;--------------------------------------------------------------------
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| 56 | %macro WAIT_UNTIL_SAFE_CGA_WRITE 0
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| 57 | %%WaitUntilNotInRetrace:
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| 58 | in al, dx
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| 59 | shr al, 1 ; 1 = Bit 0: A 1 indicates that regen-buffer memory access can be
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| 60 | ; made without interfering with the display. (H or V retrace)
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| 61 | jc SHORT %%WaitUntilNotInRetrace
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| 62 | %%WaitUntilNextRetraceStarts:
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| 63 | in al, dx
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| 64 | shr al, 1
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| 65 | jnc SHORT %%WaitUntilNextRetraceStarts
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| 66 | %endmacro
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| 67 |
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| 68 |
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| 69 | %endif ; CGASNOW_INC
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