Chapter 3 of the "Basic Input/Output" course covers essential concepts related to how computer systems interact with input/output (I/O) devices. This chapter delves into different methods of accessing these devices, the role of I/O interfaces, and their implications on system design.
1. **Accessing I/O Devices**
- In a computer system, various components communicate through an interconnection network, which includes both memory and I/O devices.
- The concepts of addressing space and memory access are applicable to I/O devices as well. Each device must have addressable locations that can be accessed using Load and Store instructions.
- These locations are implemented as I/O registers, allowing data transfer between the CPU, memory, and I/O devices.
2. **Memory-mapped I/O**
- In this approach, I/O devices and memory share the same address space, meaning that no special commands are needed for I/O operations. Instead, I/O operations resemble memory reads and writes.
- For instance, an instruction like "Load R2, DATAIN" loads the contents of the DATAIN register (an input device) into register R2, while "Store R2, DATAOUT" stores the content of R2 into the DATAOUT register (an output device).
- The advantage of memory-mapped I/O is its simplicity, as any instruction capable of accessing memory can handle I/O transfers. However, it consumes valuable memory address space, which could be used for other purposes.
3. **Separated I/O (Isolated I/O)**
- In contrast to memory-mapped I/O, separated I/O uses distinct address spaces for I/O devices. Special I/O instructions like IN and OUT are employed for data transfers.
- This approach reduces the number of address lines required by I/O devices, making them simpler. Nevertheless, a separate I/O address space doesn't always imply physically separate address lines.
4. **I/O Device Interface**
- To cope with the diversity of I/O devices, their varying data rates, formats, and speeds, an I/O device interface acts as a mediator between the device and the interconnection network.
- The interface facilitates data transfer and the exchange of status and control information, typically including data, status, and control registers that can be accessed via Load and Store instructions.
- The interface plays a crucial role in overcoming the speed difference between the CPU and I/O devices, ensuring smooth communication and synchronization.
In summary, the chapter focuses on two main methods of accessing I/O devices – memory-mapped and separated I/O – each with its advantages and disadvantages. It also highlights the importance of I/O device interfaces in managing the complexity of connecting different peripherals to the system. Understanding these fundamentals is vital for designing efficient computer systems that can effectively interact with a wide range of input and output devices.
