README
¶
Test7800 is an experimental emulator for the Atari 7800. It's not complete and is missing some important features but it plays many of the 7800 ROM files that are available.
It supports a78 files and will emulate regular "flat" ROM files and also "supergame" ROM files. It does not yet emulate the POKEY chip and similar hardware.
The 6502, TIA and RIOT emulation is taken from Gopher2600 and is therefore well tested. The implemenation of the MARIA is new to this project.
Basic Usage
Running the program from the desktop icon will open a file selection dialog. Opening a 7800 ROM will cause the emulation window to open.
Only one-button and two-button joysticks for the first player are supported for now. Also, the keyboard must be used. The cursor keys control the stick and the space bar is the fire button. The 'B' key acts as the second fire button.
A command line debugger is available if the program is run from a terminal. In this case, the ROM file should be specified as part of the command line (eg. test7800 centipede.a76). The debugger will start in a halted state. To run the emulation from this point, type RUN in the terminal.
Pressing Ctrl-C when the emulation is running will cause it to halt and to resume the debugger.
The debugger is currently very basic and missing a lot of features. However, some useful commands include STEP, RESET, CPU, MARIA, DL, DLL, VIDEO, INPTCTRL, RAM7800, RAMRIOT.
A useful option to the program is the -overlay argument. (eg. test7800 -overlay centipede.a76)). This adds an additional overlay to the TV screen, showing the state of the MARIA at each point in the display. The colours in the overlay are as follows
| Colour | Meaning |
|---|---|
| Red | DMA Active |
| Blue | WSYNC Active |
| Green | CPU in Interrupt |
| Orange | CPU in Interrupt (stalling for DMA) |
By default, the NTSC BIOS is used. To select a PAL BIOS use the -tv argument:
test7800 -tv=pal centipede.a76
If you want the emulation to ignore the BIOS startup routine use the -bios argument:
test7800 -bios=false centipede.a76
Limitations and Future
This emulation was developed in order to gain an understanding of the Atari 7800 and so is missing many features. The debugger in particular only exists so that I could more easily debug the emulator itself during development. It probably isn't that useful for ROM development as it currently exists.
The ultimate plan is to combine this 7800 emulation with Gopher2600. However, it is proving to be a convenient stand-alone emulator and so is being released for general consumption. The integration with Gopher2600 will happen but probably not any time soon.
Resources Used
References to "7800 Software Guide" in comments are referring to this wiki page. This wiki is part of a larger set of 7800 related articles: Atari 7800 Development Wiki Home
Atari 7800 Difficulty Switches Guide
Common Emulator Development Issues
Has Anyone Worked on an FPGA Atari 7800?
Acknowledgements
Zachary Scolaro helped with the MARIA emulation, particular to get it off the ground when I wasn't sure about it at all. And Rob Tuccitto has provided much advice and links to information about the 7800 internals. Thanks to both.
Documentation
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There is no documentation for this package.
Source Files
Directories
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| Path | Synopsis |
|---|---|
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Package coprocessor contains the helper functions for cartridge coprocessors.
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Package coprocessor contains the helper functions for cartridge coprocessors. |
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faults
Package faults records memory faults generated by a coprocessor.
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Package faults records memory faults generated by a coprocessor. |
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Package crunched provides the Data interface.
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Package crunched provides the Data interface. |
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arm
Package arm imlplements the ARM7TDMI instruction set as defined in the ARM7TDMI Instruction Set Reference:
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Package arm imlplements the ARM7TDMI instruction set as defined in the ARM7TDMI Instruction Set Reference: |
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arm/architecture
Package architecture defines the Map type that is used to specify the differences in cartridge and ARM archtectures.
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Package architecture defines the Map type that is used to specify the differences in cartridge and ARM archtectures. |
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arm/rng
Package rng contains an implementation of a RNG peripheral found in some ARM CPU packages.
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Package rng contains an implementation of a RNG peripheral found in some ARM CPU packages. |
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arm/timer
Package timer contains implementations of timer peripherals found in the various ARM CPU packages.
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Package timer contains implementations of timer peripherals found in the various ARM CPU packages. |
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cpu
Package cpu emulates the 6507 microprocessor found in the Atari VCS.
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Package cpu emulates the 6507 microprocessor found in the Atari VCS. |
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cpu/execution
Package execution tracks the result of instruction execution on the CPU.
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Package execution tracks the result of instruction execution on the CPU. |
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cpu/instructions
Package instructions defines the table of instruction for the 6507.
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Package instructions defines the table of instruction for the 6507. |
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cpu/instructions/generator
command
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cpu/klaus2m5
Package klaus2m5 contains the various 6502 functional tests as created/maintained by Klaus Dormann.
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Package klaus2m5 contains the various 6502 functional tests as created/maintained by Klaus Dormann. |
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cpu/registers
Package registers implements the three types of registers found in the 6507.
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Package registers implements the three types of registers found in the 6507. |
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cpu/registers/test
Package test contains functions useful for testing CPU registers.
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Package test contains functions useful for testing CPU registers. |
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memory/external/elf
Package ace implements the ELF cartridge mapper.
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Package ace implements the ELF cartridge mapper. |
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tia/audio
Package audio implements the audio generation of the TIA.
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Package audio implements the audio generation of the TIA. |
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tia/audio/mix
Package mix is used to combine two distinct sound sources into either a mono or stereo signal.
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Package mix is used to combine two distinct sound sources into either a mono or stereo signal. |
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Package logger is the central log repository for gopher2600.
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Package logger is the central log repository for gopher2600. |
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Package resources contains functions to prepare paths for test7800 resources.
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Package resources contains functions to prepare paths for test7800 resources. |
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fs
Package fs is an abstraction for OS/filesystem functions that may be missing or require special handling.
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Package fs is an abstraction for OS/filesystem functions that may be missing or require special handling. |
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unique
Package unique contains functions that compose filenames that should be unique on the filesystem.
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Package unique contains functions that compose filenames that should be unique on the filesystem. |
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Package test contains helper functions to remove common boilerplate to make testing easier.
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Package test contains helper functions to remove common boilerplate to make testing easier. |
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Package version provides a version string that can be used to indicate the version number of the project.
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Package version provides a version string that can be used to indicate the version number of the project. |
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httpd
command
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