I/O system (i)

The development of the input and output system can be broadly divided into 4 stages
1. Early stages

Characteristics:
1.1 Each IO device has a separate logic circuit and CPU connection.
1.2 The input and output process needs to pass through the CPU, interspersed in the program running process, processing IO when the CPU stop calculation
1.3 The logic control circuit of each IO device is integral to the controller of the CPU, which makes it difficult to increase or decrease
2. Interface module, DMA phase

Characteristics:
The 2.1 interface has a data path and a control path, as a buffer and a string and conversion, the transmission of data at the time of the execution of the interrupt, not completely parallel.
2.2DMA, there is a direct data path between IO device and main memory, and resource utilization is improved.
3 Channel Structure

Large computer in the IO device, data transmission is frequent, using DMA, increase the cost, DMA interface simultaneously access main memory conflict. CPU management of many DMA interfaces can also affect efficiency.
Features: 3.1 can be seen as a processor with special functions. Based on the CPU's IO instruction to start, stop or change the working state, slave CPU of a dedicated processor. IO devices are not directly managed in the processing of input and output CPUs.
4. Stage with IO processor.
4.1 Independent host work, can complete code conversion, format processing, data block monitoring and other operations.

Input/output System composition
IO software
Main tasks: 1 entering a user-written program into the host
2 operation result output
3 Input/output coordination
IO directives are generally divided into:
1. Enter data from IO into the host
2. From the host to the IO device
3. Status Test
4. Form Operation commands
Channel directives: instructions specifically set for the IO system, typically indicate the first address of the data group involved in the transmission, the number of bytes transmitted, and the device code of the equipment.

The channel control word CCW, which can be stored in main memory, is executed by the channel from the primary access.
IO instruction mainly completes the opening and stops the IO device. IO transmission is done by the channel instruction.


IO hardware
Mainly interface and IO devices
One channel can be connected to multiple device controllers.
A device controller can also be connected to multiple devices of the same type.

IO devices and hosts

1.IO Device Encoding method
There are two ways of unifying addressing and not unifying addressing. A unified addressing is the IO address as part of the storage address. Non-uniform programming is to separate the IO address and the storage address, all the IO access must use the proprietary IO instructions.
2. Device addressing
Each device has a device number, which is indicated directly by the Device Code field of the IO instruction.
3. Transfer Mode
Close range, multiple data lines, fast, parallel transmission
Serial transmission, long distance, slow speed

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1 Immediate Response
2 asynchronous work using a response signal contact, one should one answer
3 Synchronous work with synchronous time-mark contact

IO device and host connection mode
Radiant and Bus-type



IO device and host information transfer method
1. Program Query method
The CPU is constantly querying the IO device for readiness. CPU and IO are serial and CPU utilization is not high.
2. Program Interrupt mode
After the CPU starts the IO, it continues to execute its own program when IO is ready to make an interrupt request to the CPU and then the CPU accordingly.
For the CPU to transmit a batch of data, the CPU starts the IO device repeatedly, and the response is interrupted until the data transfer is complete.
3.DMA
There is a data path between main memory and IO device, and main memory and IO Exchange do not occupy CPU

I/O system (i)