CHANNEL CONTROL SYSTEM HAVING DEVICE CONTROL BLOCK AND CORRESPONDING DEVICE CONTROL WORD WITH CHANNEL COMMAND PART AND I/O COMMAND PART 5
This is a continuation of copending application Ser. No. 07/078,886 filed on July 29, 1987 now abandoned.
BACKGROUND OF THE INVENTION ]Q
1. Field of the Invention
The present invention is related to a channel unit control system in a data processing system and, more particularly, to a channel control system that is connectable to any intelligent I/O controller with changes only 15 in software.
2. Description of the Related Art
A data processing system usually consists of a central processing unit (CPU), a main storage unit, one or more channel units, I/O (input/output) devices and I/O con- 20 trailers provided between the channel units and the I/O devices.
Conventional channel units are roughly classified into two types. The first type is for relatively low intelligence and low speed devices in which the channel unit 25 itself interprets I/O commands. The I/O commands are issued by software in the CPU to designate a specific I/O device to do a specific operation and directly controls the I/O device. Therefore, the structure and/or control program of a first type channel unit is special- 30 ized for a specific I/O device and cannot control other kinds of I/O devices. If a new I/O device, especially one with higher or enhanced intelligence, is added to the data processing system, a new channel unit must be developed. In addition, new software which utilizes the 35 newly defined I/O commands must be developed, too.
The second type of channel unit is for relatively high intelligence I/O devices and operates with the aid of I/O controllers. A channel unit of the second type transfers an I/O command from software to the I/O 40 controller as it is, without interpreting the contents thereof, and then the I/O controller interprets the transferred command and informs the channel unit of the necessity for a data transfer and the direction thereof. The second type of channel unit is more flexible than 45 the first type and can handle greater varieties of I/O devices and I/O controllers, because the channel unit itself does not use the contents of I/O commands and leaves precise control of the I/O device to the I/O controller. 50
The second type, however, still has a disadvantage in that each channel unit is, in reality, limited in what kind of I/O device can be connected thereto. For example, a channel unit for a sequential access device, i.e., magnetic tape unit, cannot be used for a direct access de- 55 vice, i.e., magnetic disk unit. This is because the I/O command format is different for each kind of I/O device and thus, each channel unit must be designed to be able to handle the specific command format. Thus, if a certain system having only a magnetic tape file unit is 60 required to enhance its performance by introducing a magnetic disk file unit, a new channel unit also must be introduced or newly developed.
As an alternative, a channel unit may be designed to handle multiple command formats, but will require a 65 large amount of hardware at considerable cost and additional information will be required to identify the command format of the I/O command.
Furthermore, the second type of channel unit has another problem in that the data transfer can be prepared only after the controller informs the channel unit of necessary information, and therefore the data transfer speed is limited.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a general-purpose channel unit which, without changing any function thereof, can be connected to various types of I/O devices or I/O controllers thereof.
Another object of the present invention is to provide a general-purpose channel unit which can control t/O devices or I/O controllers without conscious of the contents of I/O commands.
Yet another object of the present invention is to provide a general-purpose channel unit which can be informed of information, which is necessary to carry out the operation of the I/O command, independently from the I/O command itself.
Still another object of the present invention is to provide a general-purpose channel unit which can perform data transfer in high speed.
To achieve the foregoing and other objects of the present invention and in accordance with the purpose of the invention, there is provided a general-purpose channel control system in which a channel command of a format being common to different types of I/O devices is sent to the channel unit together with the I/O command whose format may be different depending on the type of the I/O device.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of the data processing system where the present invention is applied;
FIG. 2 is an explanatory diagram of flows of commands and status information in the present invention;
FIG. 3 is an exemplary format of an I/O command in the present invention;
FIG. 4 is a flowchart of the channel operation in the present invention;
FIG. 5 is a flowchart of the controller operation in the present invention;
FIG. 6 is a block diagram of an I/O controller in the present invention;
FIG. 7 is a format for an end status in the present invention; and
FIG. 8 is a format for a sense byte in the present invention.
DESCRIPTION OF THE PREFERRED
FIG. 1 illustrates a system configuration of the present invention including: a central processing unit or CPU 1; a main storage unit (MSU) 2; channel unit 3; a general-purpose interface 12, such as an RS232C or IEEE 488 link, etc.; I/O controllers 13-0 to 13-m; and I/O devices 11-0 to 11-n. Each controller can be connected with a plurality of I/O devices. In MSU 2, there are provided command regions 21 for channel and I/O commands and status regions 22 for various status information.
The channel unit 3 includes: a bus controller 31 for controlling the system bus 4 between the CPU 1 and the channel unit 3; a direct memory access controller (DMAC) 32; a memory address register (MA) and a byte count register (BC) 33; a data buffer (BF) 34; channel control registers (CCR) 35 for storing various con