Use Of Microprogramming Research Articles

A microcode-based environment for noninvasive performance analysis

We have developed an environment which allows us to collect data for performance analysis by modifying the microcode of a VAX 8600. This use of microprogramming permits data to be collected with minimal system perturbation (i.e. the data is almost as good as that obtained with a hardware monitor) but at the cost and with the ease of use of a software simulator. In this paper we describe the environment that we have developed and present two examples of its use. The first example, procedure call instrumentation, illustrates a technique for gathering data on how certain architectural features are used. The second example, instruction tracing, illustrates a technique for collecting data that can then be used in trace—driven simulation.

A microprogramming language at register transfer level

The main purpose of our study is the development of software tools to aid in user microprogramming and the use of microprogramming to improve the performance of computer systems. Our main tool is the register transfer language REGTRAL. Its design objectives (minimal prerequisite hardware knowledge, readable and structured microprograms) are discussed and its main features and implementation method are described. In addition, REGTRAL microprograms are storage independent due to the automatic storage allocation process. A number of applications, some already implemented, some still in the planning stage, show the efficient use of user microprogramming and the usefulness of the REGTRAL language in this area. Finally REGTRAL is emphasized to be easily adaptable and extensible and various high-level extensions are proposed.

An approach to firmware engineering

Although microprogramming has only been a research topic for the past 10 years, the concept is nearly as old as computers. 1 Wilkes originally defined microprogramming as a systematic and orderly approach to the design of the control section of a computer. Rather than using an ad hoc approach with counters and decoders to generate control signals, Wilkes proposed that the control be organized as a matrix. This memory like approach to control remained largely of academic interest until the late 1950s. The first large-scale microprogrammed computer was the IBM 7950 in 1961. However, it was the introduction of the IBM SystemJ360 line (with all but the largest system microprogrammed) that revived interest in microprogramming. The advance in speed and the reduction in cost of read-only memory (ROM) technology transformed microprogramming from an academic concept of mild theoretical interest to a practical approach to the design of commercial computers. 2 IBM was able to offer several internally different models with the same instruction set in order to provide a spectrum of cost and speed through the use of microprogramming. With the success of the 360, several microprogrammed computers were and are being built. In the late 60' s some manufacturers made microprogramming available to the users. Nearly all computer manufacturers have at least one computer implemented via microprogramming, and the expanding list of manufacturers that provide user microprogrammable computers include Burroughs (E 1700), Control Data Corporaton (Cyber-17), Data General (Eclipse), Digital Equipment Corporation (PDP-11160) and Hewlett Packard (HP-21MX). This has expanded the potential domain of microprogrammers from computer architects to systems and applications programmers. While microprogramming and ordinary programming have existed for almost the same amount of time, little of the considerable research in programming languages and methodologies has impacted the microprogramming field. Unfortunately, the following statement is a fairly accurate description of the state of the microprogramming: 3

Special Feature: Nanoprogramming vs. Microprogramming

Vertical microprogramming (or, as others say, functional microprogramming or firmware) was introduced in contrast with Wilkes' microprogramming (generally called horizontal or structural microprogramming), and has greatly enhanced the use of microprogramming in control design and implementation. As applied today, the former technique is not yet a way of designing control structures, but an additional software level whose implications in the system are not well clarified.

On the use of ‘top stack sets’ for the storage management of a paged stack machine

The development of a storage management scheme for MEMBERS, an emulated stack machine incorporating a virtual store and paging, is described. The approach used employs an analogue of the ‘working set’ concept of Denning. Information contained in the activation stack for each process is used to indentify a ‘Top Stack Set’ for the process. The set of all the top stack sets defines the pages that are held in main storage. The architecture of the MEMBERS machine incorporates an activation stack in which pointers can be distinguised from other data. The basic programming language for the machine is designed to encourage a modular structure for programs, so that activation records in the stack for the recently entered procedures contain pointers to an approximation of the working set. The use of microprogramming for the implementation of the storage management system is also discussed and some preliminary estimates of its performance are given.

MEMBERS - a Microprogrammed Experimental Machine with a Basic Executive for Real-time Systems

The aims and methods of a project investigating the direct interpretation of a high level language and operating system by microprogram on a small machine are outlined. Some features of the language specifically designed for interpretation by microprogram are described in the context of other related work. Some factors involved in the use of microprogramming as a system development method are discussed.

MEMBERS--A Microprogrammed Experimental Machine with a Basic Executive for Real-time Systems

The aims and methods of a project investigating the direct interpretation of a high level language and operating system by microprogram on a small machine are outlined. Some features of the language specifically designed for interpretation by microprogram are described in the context of other related work. Some factors involved in the use of microprogramming as a system development method are discussed.

Programming systems and languages 1965-1975

In spite of impressive gains by PL/I, Fortran and Cobol remain the languages in which most of the world's production programs are written and will remain so into the foreseeable future. There is a great deal of theoretical interest in Algol 68 and in extensible languages, but so far at least they have had little practical impact. Problem-oriented languages may very well become the most important language development area in the next five to ten years. In the operating system area all major computer manufacturers set out to produce very ambitious multiprogramming systems, and they all ran into similar problems. A number of university projects, though not directly comparable to those of the manufacturers, have contributed greatly to a better understanding of operating system principles. Important trends include the increased interest in the development of system measurement and evaluation techniques, and increased use of microprogramming for some programming system functions.

Some Notes on Speeding Up Certain Loops by Software, Firmware, and Hardware Means

Some ways of speeding up certain loops by software, firmware, and hardware means are discussed in this note. The importance of the inner loop calculation is emphasized and a simple, though as yet unused, programming technique is presented whereby the inner loop time may be reduced by approximately 20 percent. The general problem of a program with many loops is then considered and a method is indicated for obtaining the maximum speedup by means of the technique described earlier. Turning to firmware, it is shown how, by altering the normal algorithm used for the inner loop calculation, a very substantial speedup can be achieved with the use of microprogramming (above and beyond the savings in instruction decoding time). Finally, a means is considered whereby a computer can alter its own hardware, so as to achieve a speedup of several orders for loops in which the resolution of decision tables accounts for a significant portion of the iteration time.

A Study in Microprogrammed Processors: A Medium Sized Microprogrammed Processor

A frame of reference is established for evaluating the various philosophies or approaches to the microprogramming of control logic. Three new measures for analyzing microprogramming philosophies are introduced: monophase versus polyphase, parallel versus serial, and versus encode. The terms monophase, polyphase refer to how long the microinstruction is valid. Parallel, serial refer to the method used to determine the next instruction to be executed. Encode, little encode refor to the degree of encoding in the microinstruction word. The relative merits of the extremes of these new measures are discussed. Then an example of the use of microprogramming for control logic is explored; specifically Univac's C/SP Processor is microprogrammed. It is then shown that this processor would have a cost and performance comparable with the actual C/SP version now being tested which uses conventional control logic. Moreover, it would have the flexibility and simplicity inherent in microprogramming.

Optimization Strategies for Microprograms

With increased use of microprogramming in present computer systems, the need arises to automate the checking and optimization of microcode. This paper reviews the optimization objectives, characterizes microprogranis, and discusses the machine structure. A translator from machine code to microcode appears feasible and is described. Some compiler techniques are reviewed and adapted to improve microprograms by studying operational interaction. Microprogram characteristics permit additional methods to reduce the computation effort. The techniques are integrated into a scheme implemented for optimizing a simulated machine.