OS device controller

Controller points:

• Status Register: Inform the CPU of the status of the current device, such as: working, completed
• Command Register: CPU sends commands to devices
• Data Register (Data Register): CPU transfers data to IO

I/O device points:

• Block Device: store data in fixed blocks, each block has its own address, such as: hard disk, USB
• Character Device (Character Device): Send or receive character streams in units of characters, character devices are not addressable, such as: mouse

Block device: data is large, generally has a data buffer

• CPU writes data to the controller: put a batch of data in the buffer and send it to the device
• The CPU reads data from the controller: a batch of data is stored in the buffer, and then copied to the memory
• Purpose: Reduce frequent transmission of equipment

Communication method between CPU and register/data buffer:

• Port I/O: Assign I/O ports to control registers, and operate these registers through instructions
• Memory-mapped I/O: Map control registers into memory space, read and write data buffers