This is called "bus master" mode, but for no particular reason people continue to refer to this mode as "DMA" even though the old DMA controller is long gone. The idea behind memory mapping is that a device will be. Memory-mapped I/O uses the same mechanism as memory to communicate with the processor, but not the system's RAM. Not exactly, which is why the diagram in the question doesn't quite depict memory-mapped I/O. So it's possible for, say, a RAID controller card to move any data it likes to or from the host at any time it likes. So basically you access the device controller registers through memory. Because the I/O address is the same, the DMA controller is doing the exact same operations as a CPU would, but a little more efficiently and allowing some freedom to keep running in the background (though possibly not for long as it can't talk to memory).įast-forward to the days of PCI, and the bus protocols got a lot smarter: any device can initiate a transfer. IO mapped I/O In this method separate address space is given to IO devices. This was a piece of hardware that sat up by the CPU and initiated transfers to move data from a device's I/O address to memory, or vice versa. memory can also be performed on peripherals.
using System using System.IO. A compromise solution was invented: the DMA controller. The following example opens a memory-mapped file named ImgA that has already been created from a file on disk (as shown in the example for the CreateFromFile(String) method). In order to move data from devices to host memory autonomously, there was no support in the ISA bus protocol for devices to initiate transfers.
The simple way to access data was to execute lots of CPU instructions to transfer data one word at a time from an I/O address to a memory address (sometimes known as "bit-banging.") In this video, i have explained Memory Mapped IO and IO Mapped IO in 8085 Microprocessor by following outlines:0. Most devices used I/O space for both the control interface and the bulk data-transfer interface. These were two different address spaces, accessed with different bus protocol and different CPU instructions, but able to talk over the same plug-in card slot. Since others have already answered the question, I'll just add a little bit of history.īack in the old days, on x86 (PC) hardware, there was only I/O space and memory space.
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