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 : 11.10.2010 |
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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_Stosb |
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28 | %elifidn %1, stosw |
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29 | call CgaSnow_Stosw |
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30 | %elifidn %1, rep movsb |
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31 | call CgaSnow_RepMovsb |
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32 | %else |
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33 | %error "Invalid instruction passed to WAIT_RETRACE_IF_NECESSARY_THEN" |
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34 | %endif |
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35 | %else ; No CGA snow prevention |
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36 | %ifidn %1, rep movsb |
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37 | eSEG_STR rep, es, movsb |
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38 | %else |
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39 | %1 ; Single instruction |
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40 | %endif |
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41 | %endif |
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42 | %endmacro |
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43 | |
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44 | |
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45 | ;-------------------------------------------------------------------- |
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46 | ; WAIT_UNTIL_SAFE_CGA_WRITE |
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47 | ; Parameters: |
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48 | ; DX: CGA Status Register Address (3DAh) |
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49 | ; Returns: |
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50 | ; Nothing |
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51 | ; Corrupts registers: |
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52 | ; AL |
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53 | ;-------------------------------------------------------------------- |
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54 | %macro WAIT_UNTIL_SAFE_CGA_WRITE 0 |
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55 | %%WaitUntilNotInRetrace: |
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56 | in al, dx |
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57 | shr al, 1 ; 1 = Bit 0: A 1 indicates that regen-buffer memory access can be |
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58 | ; made without interfering with the display. (H or V retrace) |
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59 | jc SHORT %%WaitUntilNotInRetrace |
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60 | %%WaitUntilNextRetraceStarts: |
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61 | in al, dx |
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62 | shr al, 1 |
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63 | jnc SHORT %%WaitUntilNextRetraceStarts |
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64 | %endmacro |
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65 | |
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66 | |
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67 | %endif ; CGASNOW_INC |
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