ISA DMA: Difference between revisions
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(→ISA DMA Background: Yes, this kind of an appendix.) |
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== ISA DMA Background == |
== ISA DMA Background == |
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'''ISA DMA''' (''Industry Standard Architecture Direct Memory Access''), like ISA itself, is an appendix for modern PCs. It is used by the |
'''ISA DMA''' (''Industry Standard Architecture Direct Memory Access''), like ISA itself, is an [https://en.wikipedia.org/wiki/Appendix_(anatomy) appendix] for modern PCs. It is used by the |
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internal floppy disk controller, ISA sound cards, ISA network cards, and parallel ports (if they support ECP mode). Whilst interrupt, keyboard |
internal floppy disk controller, ISA sound cards, ISA network cards, and parallel ports (if they support ECP mode). Whilst interrupt, keyboard |
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and timer interface circuits have obvious and relevant uses, the ISA DMA controller and its programming interface are still well and truly stuck in the |
and timer interface circuits have obvious and relevant uses, the ISA DMA controller and its programming interface are still well and truly stuck in the |
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bus. Real code should separate the two "out 0x4" and "out 0x5" calls with an "out" to some other port. |
bus. Real code should separate the two "out 0x4" and "out 0x5" calls with an "out" to some other port. |
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< |
<source lang="asm"> |
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initialize_floppy_DMA: |
initialize_floppy_DMA: |
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; set DMA channel 2 to transfer data from 0x1000 - 0x33ff in memory |
; set DMA channel 2 to transfer data from 0x1000 - 0x33ff in memory |
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out 0x0a, 0x02 ; unmask DMA channel 2 |
out 0x0a, 0x02 ; unmask DMA channel 2 |
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ret |
ret |
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</source> |
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</syntaxhighlight> |
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Once you have set up your start address and transfer length you do not need to touch it again, if you are using autoinit. Once reading or writing |
Once you have set up your start address and transfer length you do not need to touch it again, if you are using autoinit. Once reading or writing |
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is selected, you don't need to change that, either. To ''change'' selecting reading or writing you use the mode register. |
is selected, you don't need to change that, either. To ''change'' selecting reading or writing you use the mode register. |
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< |
<source lang="asm"> |
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prepare_for_floppy_DMA_write: |
prepare_for_floppy_DMA_write: |
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out 0x0a, 0x06 ; mask DMA channel 2 and 0 (assuming 0 is already masked) |
out 0x0a, 0x06 ; mask DMA channel 2 and 0 (assuming 0 is already masked) |
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out 0x0a, 0x02 ; unmask DMA channel 2 |
out 0x0a, 0x02 ; unmask DMA channel 2 |
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ret |
ret |
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</source> |
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</syntaxhighlight> |
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Some hardware, as well as VirtualPC do not support autoinit. You may want to set the Mode registers to 0x4A and 0x46 in the above routines, instead. |
Some hardware, as well as VirtualPC do not support autoinit. You may want to set the Mode registers to 0x4A and 0x46 in the above routines, instead. |
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