| 1 | ; Project name : Assembly Library |
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| 2 | ; Description : Delay functions. |
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| 3 | |
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| 4 | ; Section containing code |
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| 5 | SECTION .text |
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| 6 | |
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| 7 | ;-------------------------------------------------------------------- |
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| 8 | ; Mimimun delays (without fetching) with some CPU architectures: |
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| 9 | ; 8088/8086: 17 cycles for jump + 5 cycles for last comparison |
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| 10 | ; 286: 10 cycles for jump + 4 cycles for last comparison |
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| 11 | ; 386: 13 cycles for jump + ? cycles for last comparison |
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| 12 | ; 486: 7 cycles for jump + 6 cycles for last comparison |
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| 13 | ; |
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| 14 | ; DELAY_WITH_LOOP_INSTRUCTION |
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| 15 | ; Parameters |
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| 16 | ; CX: Loop iterations (0 is maximum delay with 65536 iterations) |
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| 17 | ; Returns: |
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| 18 | ; Nothing |
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| 19 | ; Corrupts registers: |
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| 20 | ; CX |
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| 21 | ;-------------------------------------------------------------------- |
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| 22 | %macro DELAY_WITH_LOOP_INSTRUCTION 0 |
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| 23 | %%StartOfLoop: |
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| 24 | loop %%StartOfLoop |
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| 25 | %endmacro |
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| 26 | |
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| 27 | |
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| 28 | ;-------------------------------------------------------------------- |
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| 29 | ; Delay is always at least one millisecond since |
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| 30 | ; RTC resolution is 977 microsecs. |
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| 31 | ; |
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| 32 | ; Delay_MicrosecondsFromAX |
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| 33 | ; Parameters: |
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| 34 | ; AX: Number of microsecs to wait |
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| 35 | ; Returns: |
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| 36 | ; Nothing |
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| 37 | ; Corrupts registers: |
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| 38 | ; AX |
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| 39 | ;-------------------------------------------------------------------- |
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| 40 | ALIGN JUMP_ALIGN |
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| 41 | Delay_MicrosecondsFromAX: |
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| 42 | push dx |
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| 43 | push cx |
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| 44 | |
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| 45 | xor cx, cx |
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| 46 | xchg dx, ax ; Microsecs now in CX:DX |
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| 47 | mov ah, EVENT_WAIT ; Event Wait |
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| 48 | int BIOS_SYSTEM_INTERRUPT_15h |
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| 49 | sti ; XT BIOSes return with interrupt disabled |
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| 50 | |
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| 51 | pop cx |
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| 52 | pop dx |
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| 53 | mov ax, 1 ; Prepare to wait 1 timer tick |
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| 54 | jc SHORT Delay_TimerTicksFromAX ; Event Wait was unsupported or busy |
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| 55 | ret |
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| 56 | |
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| 57 | |
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| 58 | ;-------------------------------------------------------------------- |
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| 59 | ; First tick might take 0...54.9 ms and remaining ticks |
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| 60 | ; will occur at 54.9 ms intervals. |
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| 61 | ; |
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| 62 | ; Delay_TimerTicksFromAX |
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| 63 | ; Parameters: |
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| 64 | ; AX: Number of timer ticks to wait |
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| 65 | ; Returns: |
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| 66 | ; Nothing |
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| 67 | ; Corrupts registers: |
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| 68 | ; AX |
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| 69 | ;-------------------------------------------------------------------- |
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| 70 | ALIGN JUMP_ALIGN |
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| 71 | Delay_TimerTicksFromAX: |
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| 72 | push dx |
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| 73 | |
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| 74 | sti ; Make sure that interrupts are enabled |
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| 75 | xchg dx, ax |
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| 76 | call TimerTicks_ReadFromBdaToAX |
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| 77 | add dx, ax ; DX = end time |
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| 78 | .WaitLoop: |
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| 79 | call TimerTicks_ReadFromBdaToAX |
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| 80 | cmp ax, dx |
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| 81 | jb SHORT .WaitLoop ; Loop until end time is reached |
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| 82 | |
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| 83 | pop dx |
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| 84 | ret |
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