Microassembler
Encyclopedia
A microassembler is a computer program
that helps prepare a microprogram
to control the low level operation of a computer in much the same way an assembler helps prepare higher level code for a processor
. The difference is that the microprogram is usually only developed by the processor manufacturer and works intimately with the hardware. The microprogram defines the instruction set
any normal program (including both application programs
and operating system
s) is written in. The use of a microprogram allows the manufacturer to fix certain mistakes, including working around hardware
design errors, without modifying the hardware. Another means of employing microassembler-generated microprograms is in allowing the same hardware to run different instruction set
s. After it is assembled, the microprogram is then loaded to a control store
to become part of the logic of a CPU
's control unit
.
Some microassemblers are more generalized and are not targeted at a single computer architecture. For example, through the use of macro-assembler-like capabilities, Digital Equipment Corporation
used their MICRO2 microassembler for a very wide range of computer architectures and implementations.
If a given computer implementation supports a writeable control store
, the microassembler is usually provided to customers as a means of writing customized microcode.
In the process of microcode
assembly it is helpful to verify the microprogram with emulating tools before distribution. Nowadays, microcoding experience a revival, since it is possible to correct and optimize the firmware (i.e. the microcode) of processing units sold, in order for adaptation to operating systems or for bug fixing means. However, a commonly usable microassembler for today's CPUs is not available to manipulate the microcode. Unfortunately, it is difficult to obtain open knowledge about changing the microcode because of intellectual property reasons.
How microcode can be assembled with a microassembler to control a CPU with own created machine codes on
microprogramming basis, can be understood and simulated with e-learning
tools like Mikrocodesimulator
MikroSim
on a didactial point of view.
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
that helps prepare a microprogram
Microcode
Microcode is a layer of hardware-level instructions and/or data structures involved in the implementation of higher level machine code instructions in many computers and other processors; it resides in special high-speed memory and translates machine instructions into sequences of detailed...
to control the low level operation of a computer in much the same way an assembler helps prepare higher level code for a processor
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
. The difference is that the microprogram is usually only developed by the processor manufacturer and works intimately with the hardware. The microprogram defines the instruction set
Instruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
any normal program (including both application programs
Application software
Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...
and operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s) is written in. The use of a microprogram allows the manufacturer to fix certain mistakes, including working around hardware
Hardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....
design errors, without modifying the hardware. Another means of employing microassembler-generated microprograms is in allowing the same hardware to run different instruction set
Instruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
s. After it is assembled, the microprogram is then loaded to a control store
Control store
A control store is the part of a CPU's control unit that stores the CPU's microprogram. It is usually accessed by a microsequencer. Early control stores were implemented as a diode-array accessed via address decoders, a form of read-only memory. This tradition dates back to the program timing...
to become part of the logic of a CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
's control unit
Control unit
A control unit in general is a central part of the machinery that controls its operation, provided that a piece of machinery is complex and organized enough to contain any such unit. One domain in which the term is specifically used is the area of computer design...
.
Some microassemblers are more generalized and are not targeted at a single computer architecture. For example, through the use of macro-assembler-like capabilities, Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
used their MICRO2 microassembler for a very wide range of computer architectures and implementations.
If a given computer implementation supports a writeable control store
Control store
A control store is the part of a CPU's control unit that stores the CPU's microprogram. It is usually accessed by a microsequencer. Early control stores were implemented as a diode-array accessed via address decoders, a form of read-only memory. This tradition dates back to the program timing...
, the microassembler is usually provided to customers as a means of writing customized microcode.
In the process of microcode
Microcode
Microcode is a layer of hardware-level instructions and/or data structures involved in the implementation of higher level machine code instructions in many computers and other processors; it resides in special high-speed memory and translates machine instructions into sequences of detailed...
assembly it is helpful to verify the microprogram with emulating tools before distribution. Nowadays, microcoding experience a revival, since it is possible to correct and optimize the firmware (i.e. the microcode) of processing units sold, in order for adaptation to operating systems or for bug fixing means. However, a commonly usable microassembler for today's CPUs is not available to manipulate the microcode. Unfortunately, it is difficult to obtain open knowledge about changing the microcode because of intellectual property reasons.
How microcode can be assembled with a microassembler to control a CPU with own created machine codes on
microprogramming basis, can be understood and simulated with e-learning
E-learning
E-learning comprises all forms of electronically supported learning and teaching. The information and communication systems, whether networked learning or not, serve as specific media to implement the learning process...
tools like Mikrocodesimulator
MikroSim
MikroSim
The program MikroSim is an educational software for hardware-non-specific explanation of the general functioning and behaviour of a virtual processor, running on the operating system Microsoft Windows...
on a didactial point of view.