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| ## About | ||
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| Moira is a Motorola 68000 emulator written in C++. The emulator was written with four goals in mind: | ||
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| - A high emulation accuracy, both functionally and temporally | ||
| - A high emulation speed | ||
| - The ability to easily port the code to other platforms | ||
| - The ability to emulate multiple CPU instances simultaneously | ||
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| Moira is the CPU that powers the Amiga emulator vAmiga. It is used there with great success so far. | ||
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| ## History | ||
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| Before I started the vAmiga project in early 2019, I informed myself about the existing Motorola 68k emulators at the time. What I was looking for was a throughly tested emulator with high emulation speed and good code quality. I did find such an emulator in the form of Musashi, written by Karl Stenerud, which is being used successfully in the Mame project for many years now. I had been using Musashi in vAmiga for roughly a year until I realized that it lacks one important feature: Precise inter-instruction timing information. | ||
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| In order to emulate the memory bus of the Amiga with high precision, I needed to know the number of cycles that had elapsed, for example, between the beginning of a command execution and the first or second access of the memory bus. Like most 68k emulators, Musashi only provides the total number of CPU cycles that has been consumed by the execution of a single instruction. Because cycle-exact bus timing is a crucial aspect for Amiga emulation, I came to the conclusion that more sophisticated timing control was needed to bring vAmiga to the next level. | ||
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| My search for a new CPU core had drawn my attention to the Portable68000 emulator and its successor Denise m680x0, both written by "PiCiJi". These emulators offer inter-instruction timing and thus exactly what I needed to take vAmiga to the next level. However, Denise wasn't thoroughly tested back then, but already far superior to portable68000 from a software-architectural point of view. At this point I decided to implement my own CPU based on the three CPU cores I already knew. In fact Musashi, Portable68000 and Denise m680x0 can be considered the intellectual ancestors of my CPU implementation: Moira imitates much of the concepts the three other emulators are based on. Externally, Moira might appear a bit like a clone of Musashi, because it mimics Musashi’s disassembler output down to the last character. Internally, Moira exhibits many similarities with Denise m680x0. For example, it provides exactly the same sync function that is being used by Portable68000 and Denise to count the number elapsed cycles between bus accesses. | ||
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| ## Portability | ||
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| Moira is a C++ application that complies with the C++14 standard and can therefore be compiled on most operating systems and hardware platforms. It was successfully compiled on macOS with clang and on Linux with gcc. | ||
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| ## Accuracy | ||
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| To achieve a high emulation accuracy, I have applied two different test strategies. Firstly, I developed an automated test- runner, which is also part of this repository. After downloading, compiling, and running the code from this repository, the test-runner starts automatically. It iterates over all opcodes, runs Moira and Musashi in parallel, and compares the calculated results afterwards. It executes in an infinite loop and only aborts if a discrepancy between the two CPUs is detected. | ||
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| ``` | ||
| Moira CPU tester. (C) Dirk W. Hoffmann, 2019 - 2020 | ||
| The test program runs Moira agains Musashi with randomly generated data. | ||
| It runs until a bug has been found. | ||
| Round 1 ................ PASSED (Musashi: 0.04s Moira: 0.04s) | ||
| Round 2 ................ PASSED (Musashi: 0.09s Moira: 0.09s) | ||
| Round 3 ................ PASSED (Musashi: 0.14s Moira: 0.14s) | ||
| Round 4 ................ PASSED (Musashi: 0.19s Moira: 0.18s) | ||
| Round 5 ................ PASSED (Musashi: 0.23s Moira: 0.22s) | ||
| ``` | ||
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| I also tested Moira extensively with cputester, a tool written by Toni Wilen which is now part of the Amiga emulator UAE. With cputester you can create a large number of test programs that run on the Amiga platform and test the CPU "from the inside". With cputester I created a large number of test programs that were then executed inside vAmiga. | ||
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| Based on the testing results, all Amiga features of Moira can be considered to be thoroughly tested. Please note that all features that are not used by the Amiga (such as non-autovectored interrupts or the special behaviour of the TAS command) are either unimplemented or untested yet. If you plan to use the emulation core and need these features, please let me know. I am eager to add the yet missing features to the emulator. | ||
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| ## Feature Overview | ||
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| Besides the emulation core Moira comes with an integrated disassembler and a debugger. | ||
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| Its debugging capabilities include setting breakpoints and watchpoints as well as logging the instruction stream. vAmiga makes extensive use of these functions by making them accessible in its CPU inspector panel. It is a nice example of how Moira can be utilized in a real-world application: | ||
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| ## Credits | ||
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| I am grateful to | ||
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| - Karl Stenerud for writing [Musashi](https://github.com/kstenerud/Musashi), | ||
| - „PiCiJi“ for writing [Denise m680x0](https://bitbucket.org/piciji/denise/src/master/emulation/processor) and [Portable68000](https://sourceforge.net/projects/portable68000), | ||
| - Toni Wilen for writing cputester. | ||
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| *Nanos gigantum humeris insidentes*. | ||
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| ## Where to go from here? | ||
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| - [The Moira wiki pages](https://github.com/dirkwhoffmann/Moira/wiki) | ||
| - [vAmiga on GitHub](https://github.com/dirkwhoffmann/vAMIGA) | ||
| <p align="center"> | ||
| <a href = "https://dirkwhoffmann.github.io/Moira"><img src="https://dirkwhoffmann.github.io/Moira/images/redirect.png"></a> | ||
| </p> |