Electrical computers and digital processing systems: interprogra – Device driver communication
Reexamination Certificate
1999-03-26
2004-07-20
An, Meng-Al T. (Department: 2126)
Electrical computers and digital processing systems: interprogra
Device driver communication
C719S328000
Reexamination Certificate
active
06766519
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to interfaces used by programs to control and respond to components of a computer system and more specifically to the interfaces used by programs to control and respond to hardware environments.
2. Description of the Prior Art
When all is said and done, what a computer program does is control and respond to hardware devices. When a user types a character on the keyboard, the program executing on the computer system responds to the input from the keyboard hardware by causing the computer system to execute instructions which in turn cause the display terminal to display the typed character. Because the computer program controls and responds to hardware devices, the instructions in the program vary depending on the kinds of hardware devices being used.
One example of this is the form of the instructions themselves: each kind of computer has a set of instructions defined for it, and a program which is to execute on that kind of computer must be written using that set of instructions. Another example is the kinds of peripheral devices in the computer system. A peripheral device is a device such as a keyboard, a display, a disk drive, or a printer that works with the computer but is separate from it. A program written for a system with one kind peripheral device will not work on a system that uses a different kind of peripheral device, even though both systems have a computer that executes the same instruction set. For example, a program written for one kind of keyboard will not work with another kind of keyboard.
From early on, programmers have taken measures to decrease the dependence of their programs on hardware. The general technique for doing this has been for the programs to deal with the hardware in logical rather than physical terms to the greatest extent possible. The problems posed by the different instruction sets employed by various computer systems have been solved by writing the programs in high-level languages, which deal in logical operations such as assignment of a value to a variable or branching according to the value of a variable rather than in the physical operations performed by a given computer system's instruction set. A compiler program then automatically translates the program written in the high-level language into an equivalent program written in the given computer's instruction set.
Compilers have not, however, been able to solve the problem of dealing with differing peripheral devices. That problem is dealt with at present by the computer system's operating system. An operating system is a computer program that manages the hardware making up a computer system and presents the hardware to the applications programmer as a set of generic entities. The applications programmer thus writes code for a generic keyboard, display, or file system and the operating system deals with the peculiarities of the system's actual keyboards, displays, and file systems. For example, from the point of view of the applications programmer, a keyboard is simply a source of character codes, and the operating system provides the applications programmer with a generic keyboard that is exactly that, while itself dealing with the peculiarities of the particular keyboards being used in the computer system.
FIG. 1
shows a typical computer system
101
. Computer system
101
includes a processor
103
, memory
111
, and a number of peripheral devices
105
(
0
. . . n). Processor
103
and peripheral devices
105
(
0
. . . n) are coupled to memory
111
by bus
109
, and can thus read data
112
from and write data
112
to memory
111
. Processor
103
further reads instructions
114
from programs stored in memory
111
and executes them. Where the program involves peripheral devices, processor
103
responds to the instructions relevant to the peripheral devices by sending control signals to them. When something happens in a peripheral device that requires intervention of processor
103
, the peripheral device sends an interrupt to processor
103
. In response to the interrupt, processor
103
executes code in memory
111
. For example, when a user strikes a key on a keyboard, an interrupt results whose associated code may cause processor
103
to put the character received from the keyboard into a predetermined location in memory for later use by a program that displays characters on a display device.
The programs in memory
111
include one or more applications programs
123
, operating system
117
, and BIOS
113
, a low-level program that provides basic I/O services to operating system
117
. BIOS
113
, processor
103
and peripheral devices
105
(
0
. . . n) make up hardware environment
102
of system
101
. The makers of hardware environment
102
generally provide a BIOS
113
suited for the environment they are providing.
Operating system
117
makes it possible for applications program
123
to ignore the peculiarities of peripheral devices
105
(
0
. . . n) and of the interrupts they provide to processor
103
. Operating system
117
presents an operating system interface
121
to applications program
123
in which the facilities of computer system
101
appear as generic devices. Thus, a peripheral device
105
(
i
) which is a keyboard appears to application program
123
simply as a source of characters. Operating system
117
is made up of hardware environment-independent code and data
118
, which is not affected by the peculiarities of hardware environment
102
, and hardware-dependent code and data
119
, which is. Two important components of hardware-dependent code and data
119
are device drivers
120
and interrupt handlers
122
. A device driver is a program whose code is dependent on the peculiarities of a given peripheral device
105
(
i
), typically because it controls peripheral device
105
(
i
). An interrupt handler is code which processor
103
executes in response to an interrupt from a given peripheral device
105
(
i
). As one would expect, this code is also dependent on the peculiarities of the given peripheral device.
Compilers and operating systems together have made it possible for applications programs to be portable, that is, an application program written for a given operating system can be recompiled to run on any computer system that uses the operating system. However, as one would expect from the role of the operating system in dealing with the hardware environment, operating systems are not portable. Even after the code for an operating system has been recompiled so that it is made up of instructions belonging to processor
103
's instruction set, the hardware-dependent code and data
119
must be rewritten to deal with the new hardware environment
102
. This process of rewriting the hardware-dependent code and data is termed porting the operating system to the hardware environment. Porting an operating system is difficult, slow, and requires an extensive knowledge of both the new hardware environment
102
and at least the hardware-dependent code and data portion of the operating system.
What is needed is a technique which permits many hardware environments to be presented to the operating system by means of a single generic interface, thereby making it possible to replace the hardware environment-dependent code in the operating system with code that is dependent on the single generic interface, rather than a particular hardware environment. It is an object of the present invention to provide such a technique.
SUMMARY OF THE INVENTION
The invention provides a generic interface layer which executes in a hardware environment and in turn provides a generic interface to the hardware environment to a program such as an operating system that uses the generic interface layer to control and respond to the hardware environment. As mentioned above, the hardware environment includes a number of devices and produces a number of different kinds of interrupts.
The generic interface layer is made up of executable code including driver
Bong Paul A.
Burriss Michael Lee
Huff Jerry W.
Worth, III Stephen Gardner
An Meng-Al T.
EMC Corporation
Ho The Thanh
Nelson Gordon E.
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