March 2015 Archive


Memory-Mapped I/O
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Memory-Mapped I/O

Each controller has a few registers that are used for communicating with the CPU. By writing into these registers, the operating system can command the device to deliver data, accept data, switch itself on or off, or otherwise perform some action. By reading from these registers,

Direct Memory Access (DMA)
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Direct Memory Access (DMA)

Regardless of whether a CPU does or does not have memory-mapped I/O, it needs to address the device controllers to exchange data with them. The CPU can request data from an I/O controller one byte at a time but doing so wastes the CPU's time, so a different scheme, called

Interrupts Revisited
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Interrupts Revisited

We briefly introduced interrupts in "Handheld Computer Operating Systems" but there is more to be said. In a typical personal computer system, the interrupt structure is as illustrated in Figure 1. At the hardware level, interrupts work as follows. When an I/O device has finished

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