HERA: the Haverford Educational RISC Architecture

HERA, the Haverford Educational RISC Architecture, is a single architecture that can span the needs of a wide variety of upper-level undergraduate applied CS courses. It is powerful enough to introduce assembly language programming in Principles of Programming Languages and serve as a target for compilers in Compiler Design, yet simple enough to be built as a student project in Principles of Computer Organization (using, for example, Jeffery P. Hansen's tkgate simulator). It has been used to support hardware/software co-design labs in our course on Operating Systems.

The use of a single simplified architecture and a familiar development environment minimizes the overhead of introducing new architectures or simulation tools, giving us more time to focus on the material we want to discuss. Students also seem to find a certain satisfaction from building, in their undergraduate courses, an entire system from the level of AND, OR, and NOT gates up through a high-level language. The HERA system was presented (by Dave W) in a poster session (not reviewed) at SIGCSE '05 and a paper (reviewed) at CCSCE '06; more details about the educational uses of HERA can be found in the CCSCE paper.

The specification of HERA version 2.2.3 is available in either Full detail or as a Quick Reference; these can now be purchased purchased as a paperback book (the quick reference is printed in a small font on the back cover) from lulu.com. This version of the specification meets the needs of our current courses; I expect future revisions to consist of minor clarifications to the documentation, and bug fixes for tools (the HERA-C simulator, the standard library for tiger, and the Hassem assembler). The list of differences among various version numbers is also available.

The HERA-C simulator is designed to make most features of HERA assembly language available in a standard C or C++ development environment. It consists of a collection of macros that are named after HERA instructions, so that a HERA program can be compiled and debugged in a C/C++ environment like this. The current HERA-C simulator files, for HERA 2.2.3, are available as a gzipped tar file that includes the Hassem files for the tiger standard library, a list of fundamental design limitations of HERA-C (README.flaws), and a few other things.

The "Hassem" assembler is currently in "beta-test" stage and can be obtained by email request to Dave W.

I would like to thank all the students who worked with earlier version of this system for their patience, and especially Todd Miller (HC '01) for his work on HERA-C. The documentation for Version 2 of HERA was written with TeXmacs.