Editing Microassembler (section)

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A '''microassembler''' is a [[computer program]] that helps prepare a [[microcode|microprogram]], called ''firmware'', to control the low level operation of a computer in much the same way an [[Assembly language#Assembler|assembler]] helps prepare higher level code for a [[central processing unit|processor]]. The difference is that the microprogram is usually only developed by the processor manufacturer and works intimately with the [[computer hardware]]. On a microprogrammed computer the microprogram implements the operations of the [[instruction set]] in which any normal program (including both [[application software|application programs]] and [[operating system]]s) is written. 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 [[Central processing unit|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 [[Control store|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 emulation  tools before distribution. Nowadays, microcoding has experienced a revival, since it is possible to correct and optimize the firmware of processing units already manufactured or sold, in order to adapt to specific [[operating system]]s or to fix hardware bugs. However, a commonly usable microassembler for today's CPUs is not available to manipulate the microcode. Knowledge of a processor's microcode is usually considered proprietary information so it is difficult to obtain information about how to modify it.