11/20/2023 0 Comments Build io device registration![]() Though these days it's actually the LPC bus, but LPC is designed to work like ISA. Parallel port being an old-school ISA device. Of course, any such devices would be directly addressable by the CPU and not "behind" a controller. It's controlled by a single byte in the I/O address space. Simple devices may not need a data, control, and status register. Make it so reads and writes to the same I/O address actually access different registers or functions on the device. Make it so mere access (read or write) to an I/O address causes the device to do something. Hardware can be designed to react in any way the hardware designer wants to read/write requests from the CPU. What you describe in your post is a "typical" scenario, especially if I/O is on a different bus than the CPU (PCI/PCI is a good example) or you are talking to a controller rather than the actual I/O device. The status register contains bits that can be read by the host.The data-out register is written by the host to send output.The data-in register is read by the host to get input.More complex devices (e.g., disks) will have multiple control andĭoes the following quote from Operating System Concepts mean that in a device controller, a IO port has four registers?Īn I/O port typically consists of four registers, called the status,Ĭontrol, data-in, and data-out registers. a status register (readable, for determining device status - in particular, whether it is ready to receive or provide data).a control register (writable, for controlling device operation).a data register (either readable or writable, depending on whether it is an input or output device).Simple controller will have at least 3 addresses (ports) on the bus,Įach corresponding to a register in the controller Do the following two references give different claims on the relations between IO ports and registers in a device controller? What are their relations actually?ĭoes the following quote from mean that in a device controller, there is exactly one IO port for each register, and there is exactly one register for each IO port?Įach I/O device is connected to the I/O bus through a controller.
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