A7800 - the Atari 7800 Emulator

RevEng · November 17, 2021

Ah, now I get what you're saying... no, 32 unique inputs isn't possible with that method, since you need to stick to the original actions for the mapping. So you'd need a custom controller driver for that.

In your proposed controller, you'd get ghosting from simultaneous button presses. I take it that's not a problem for your planned use-case?

+Karl G · November 17, 2021

No, I think you can do all of the combinations depending on how you overlap the mappings for each of the 5 inputs. I'll have to play around with it, though. I was wondering why the Atari keyboard controllers only had 12 buttons and used the paddle lines when you could have 31 possible input combinations (not counting all off as one of them) with the normal joystick inputs.

I'm not sure what you mean by "ghosting", and I don't know if there's a hardware reason that I'm unaware of what would explain why this wouldn't work for a real controller. Obviously though it would have to be used with something specifically written for it on the software side.

RevEng · November 17, 2021

Ghosting is the term used when simultaneous key-presses aren't registered correctly. e.g. if button 1 is pressed and activates left+up, and button 2 is simultaneously pressed and activates right+up, it will be interpreted as an entirely different button that's represented by left+up+right.

The atari keypads use a different scheme, with the keypad rows being detected by the joystick directions, and the columns being selected by paddle lines. This is closer to regular keyboard wiring, and less prone to ghosting.

+Karl G · November 17, 2021

Okay, so I thought I'd try my hand at adding a new controller driver to a7800. I figured it could mostly be a clone of the vcs joystick driver with different defaults. I found the files in src/devices/bus/a7800_ctrl, made copies of joystick.cpp and joystick.h, edited them changing names appropriately, and added an entry to ctrl.cpp. Now, I can't figure out where the actual driver code is. grep has not been my friend. If you have a chance, could you please point me in the right direction? ?

RevEng · November 18, 2021

The driver is mostly in the slotted device, like the one you copied - e.g. the a7800_joy_r() routine controls what gets returned on a joystick port read, but the joystick one you picked as a basis is pretty mundane, so it's not very instructive. Have a look at a7800_joy_r() in the trackball driver, or something else that gets a bit more involved.

+Karl G · November 18, 2021

Thanks. I'm not seeing where I can define symbols needed for my new device. When I compile I get:

Compiling src/devices/bus/a7800_ctrl/minikeyboard.cpp...
In file included from ../../../../../src/devices/bus/a7800_ctrl/minikeyboard.cpp:10:
In file included from ../../../../../src/devices/bus/a7800_ctrl/minikeyboard.h:14:
../../../../../src/devices/bus/a7800_ctrl/ctrl.h:127:1: warning: 'const' qualifier on reference type 'device_type' (aka 'const emu::detail::device_type_impl &') has no effect [-Wignored-qualifiers]
DECLARE_DEVICE_TYPE(A7800_CONTROL_PORT, a7800_control_port_device)
^
/Users/kdgarris/Downloads/a7800-4.0/build/projects/sdl/mame/gmake-osx/../../../../../src/emu/device.h:236:22: note: expanded from macro 'DECLARE_DEVICE_TYPE'
                extern device_type const Type; \
                                   ^
In file included from ../../../../../src/devices/bus/a7800_ctrl/minikeyboard.cpp:10:
../../../../../src/devices/bus/a7800_ctrl/minikeyboard.h:47:1: warning: 'const' qualifier on reference type 'device_type' (aka 'const emu::detail::device_type_impl &') has no effect [-Wignored-qualifiers]
DECLARE_DEVICE_TYPE(A7800_MINIKEYBOARD, a7800_minikeyboard_device)
^
/Users/kdgarris/Downloads/a7800-4.0/build/projects/sdl/mame/gmake-osx/../../../../../src/emu/device.h:236:22: note: expanded from macro 'DECLARE_DEVICE_TYPE'
                extern device_type const Type; \
                                   ^
../../../../../src/devices/bus/a7800_ctrl/minikeyboard.cpp:18:1: warning: 'const' qualifier on reference type 'device_type' (aka 'const emu::detail::device_type_impl &') has no effect [-Wignored-qualifiers]
DEFINE_DEVICE_TYPE(A7800_MINIKEYBOARD, a7800_minikeyboard_device, "a7800_minikeyboard", "mini keyboard controller")
^
/Users/kdgarris/Downloads/a7800-4.0/build/projects/sdl/mame/gmake-osx/../../../../../src/emu/device.h:251:15: note: expanded from macro 'DEFINE_DEVICE_TYPE'
                device_type const Type = device_creator<Class, (Class##_device_traits::shortname), (Class##_device_traits::fullname), (Class##_device_traits::source)>; \
                            ^
../../../../../src/devices/bus/a7800_ctrl/minikeyboard.cpp:39:9: error: use of undeclared identifier 'construct_ioport_a7800_minikeyboard'; did you mean 'construct_ioport_a7800_joystick'?
        return INPUT_PORTS_NAME( a7800_minikeyboard );
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
               construct_ioport_a7800_joystick
/Users/kdgarris/Downloads/a7800-4.0/build/projects/sdl/mame/gmake-osx/../../../../../src/emu/ioport.h:1582:33: note: expanded from macro 'INPUT_PORTS_NAME'
#define INPUT_PORTS_NAME(_name) construct_ioport_##_name
                                ^
<scratch space>:13:1: note: expanded from here
construct_ioport_a7800_minikeyboard
^
../../../../../src/devices/bus/a7800_ctrl/minikeyboard.cpp:21:8: note: 'construct_ioport_a7800_joystick' declared here
static INPUT_PORTS_START( a7800_joystick )
       ^
/Users/kdgarris/Downloads/a7800-4.0/build/projects/sdl/mame/gmake-osx/../../../../../src/emu/ioport.h:1586:16: note: expanded from macro 'INPUT_PORTS_START'
ATTR_COLD void INPUT_PORTS_NAME(_name)(device_t &owner, ioport_list &portlist, std::string &errorbuf) \
               ^
/Users/kdgarris/Downloads/a7800-4.0/build/projects/sdl/mame/gmake-osx/../../../../../src/emu/ioport.h:1582:33: note: expanded from macro 'INPUT_PORTS_NAME'
#define INPUT_PORTS_NAME(_name) construct_ioport_##_name
                                ^
<scratch space>:12:1: note: expanded from here
construct_ioport_a7800_joystick
^
3 warnings and 1 error generated.
make[2]: *** [../../../../osx_clang/obj/x64/Release/src/devices/bus/a7800_ctrl/minikeyboard.o] Error 1
make[1]: *** [optional] Error 2
make: *** [macosx_x64] Error 2

minikeyboard.cpp

minikeyboard.h

ctrl.cpp

RevEng · November 19, 2021

Try changing this...

static INPUT_PORTS_START( a7800_joystick )

...to this...

static INPUT_PORTS_START( a7800_minikeyboard )

+Karl G · November 19, 2021

10 hours ago, RevEng said:
Try changing this...
static INPUT_PORTS_START( a7800_joystick )
...to this...
static INPUT_PORTS_START( a7800_minikeyboard )

D'oh! I missed that. Thanks again!

+Karl G · November 30, 2021

Edit: Nevermind. I needed to set the "set softresetpause off" option in 7800basic to avoid this.

Okay, so in the process of developing my MAME driver for the not-yet-existent minikeyboard controller, I believe I have discovered a bug or limitation in the emulator. While my driver exposes it, I have also reproduced it with the trakball driver. The tiny test program which is attached demonstrates it.

What happens is when a7800 registers joystick right, joystick left, and joystick down input all at the same time, it also triggers the reset switch. This is normally impossible with a joystick controller, of course, but the trackball driver can register these inputs all at once.

The attached demo program simply changes the background color every frame where it detects the reset button is pressed. To test it, load it in a7800, hit tab, go to Controller Selection, and choose cx22 trakball as the controller for the first port, then reset the emulator to have the setting take effect. If reset is never detected, the background should remain white. If it is detected, the background colors should change as you move your mouse.

Could anyone test this to confirm this issue for me? Thanks in advance. ?

ControllerReset.78b

ControllerReset.78b.a78

RevEng · December 1, 2021

Pretty sure you're triggering the 7800basic soft-reset/pause code. 7800basic implements these via impossible joystick directions. This code is disabled compile-time if the game uses a 7800basic controller driver that can generate these directions.

It looks like I need to update the manual with this. (I've posted about it a few times in the forums, including the 7800basic thread.)

+Karl G · December 1, 2021

2 minutes ago, RevEng said:

Pretty sure you're triggering the 7800basic soft-reset/pause code. 7800basic implements these via impossible joystick directions. This code is disabled compile-time if the game uses a 7800basic controller driver that can generate these directions.

It looks like I need to update the manual with this. (I've posted about it a few times in the forums, including the 7800basic thread.)

Well, that's certainly a relief. Although my sample did set the port to use the trakball to help rule out unrelated issues, so presumably the code should have been disabled in this case?

Anyway, if I know it's likely 7800basic that is causing this behavior, I can look at the code there (since it's much less of a headache than MAME source code). Thanks once again!

RevEng · December 1, 2021

You're welcome. Not sure why it wasn't disabled... I see the conditions in there.

If you're looking to disable this functionality, check std_routines.asm and just search for "soft".

+Karl G · December 1, 2021

16 minutes ago, RevEng said:

Yeah, not sure why it wasn't disabled... I see the conditions in there.

If you're looking to disable this, check std_routines.asm and just search for "soft".

It looks like you have an option for it already. I tried it, and it works for me:

   set softresetpause off

+Karl G · December 1, 2021

I spoke too soon. Some of the soft switch code in there checked for trakball, mouse, or the softresetpause option, but other parts only checked for mouse support to disable it. Here's a patch (diff -buN) that adds those checks for the other parts as well, if you would like it.

soft-switch-fix.patch

RevEng · December 1, 2021

4 hours ago, Karl G said:

I spoke too soon. Some of the soft switch code in there checked for trakball, mouse, or the softresetpause option, but other parts only checked for mouse support to disable it. Here's a patch (diff -buN) that adds those checks for the other parts as well, if you would like it.

soft-switch-fix.patch 1014 B · 1 download

Yeah, that 7800basic option was just to disable the soft-reset acting as a pause, when pause isn't disabled. It sounds complicated, but basically it means the soft-reset button can start a game (reset when pausing is disabled, as it should be during a title screen), and then act as a pause during a game when pause isn't disabled.

I don't actually have a full disable for the soft-switches yet (aside from compiling in a mouse or trackball) but I'll add one in before the next release.

+Karl G · January 7, 2022

Is there a way to change default emulator keybindings that aren't directly related to the 7800? For example, the "P" key pauses emulation (unrelated to the 7800 pause button, to be clear). Googling for MAME seems to indicate that it should be changeable via the GUI, but I don't see a way in a7800 to do that?

I was able to change it via source, but if there's a cleaner way I'd rather do that.

RevEng · January 7, 2022

Yeah, I don't see a way to do it... I suspect when you compile in only a specific mame driver, as we have for a7800, the UI gets limited to the scope of the driver only. A bit weird, but perhaps there are deeper code reasons.

I'm not familiar with the Mame UI code and how I might undo that, so I don't think this will get addressed any time soon.

+Karl G · January 7, 2022

Thanks. Okay; I'm at peace with a source code change to do it so long as I know it's a necessary kludge, and not a matter of me being dumb about it.

Shannon · January 7, 2022

You might be able to re-assign the key using the normal mame interface ( download regular mame ) and then use the resulting .cnf file or whatever it is called with A7800. Plus it might save the trouble of irritating a bunch of people who may not mind having 'p' as pause.

Edited January 7, 2022 by Shannon

Trebor · March 31, 2022

***UPDATE***

A7800 v5.0

What's new?

graphical register updates made mid-scanline are now displayed mid-scanline.
bankset bankswitching support added.
pokey emulation quality improvements.
improved lightgun emulation accuracy.
a7800dev and a7800pdev machine targets added, which display DMA usage per-scanline.
balanced palette brightness and saturation.
pokey@800 added for non-banked, supergame, and bankset formats.
os x build now defaults to opengl video. (bgfx video may not work on recent os x releases)

For all supported OS's (Linux, macOS and Windows) there is a 64-bit (x64) build.

Quick and easy portable install for Windows:

1. Download A7800, unzip to a new/clean preferred location [I.E. C:\A7800].

2. Download A7800_Optional_Files_20220331, unzip to same location as A7800.

Starting Console:

Spoiler

1. Double click A7800.exe.

2. Choose a console (Double click with mouse pointer or highlight with arrow keys and press 'Enter'), either NTSC or PAL with desired console/palette temperature: Cold, Hot, or Warm.

3. Select a console configuration (Double click with mouse pointer or highlight with arrow keys and press 'Enter'): Standard Console, High Score Cartridge, XM Expansion Module.

Selecting ROM:

Spoiler

1. After a system is started, press the ‘Tab’ key.

2. Highlight the option "Load ROM file" with arrow keys and press 'Enter', or double click with mouse pointer.

3. Perform the same respecting the available "cartridge (cart)" slot that appears.

4. Choose a ROM from the displayed "roms" subfolder on the screen; otherwise, navigate to the location of where the ROMs are stored. ROMs should have headers in proper *.a78 format.

Default Mappings:

Spoiler

1. Console: Pause = O; Select = E; Reset = T.

2. Player 1: Up, Down, Left, Right = Arrow Keys; Button 1 = Z; Button 2 = C.

3. Player 2: Up, Down, Left, Right = I, K, J, L; Button 1 = A; Button 2 = D.

Changing Controllers:

Spoiler

1. After a system is started, press the ‘Tab’ key.

2. Highlight the option "Controller Selection" with arrow keys and press 'Enter', or double click with mouse pointer.

3. Change a controller by highlighting it and then press either the left or right arrow key.

4. After a controller is changed, reset the emulator by selecting “Reset”.

***See the included illustrative manual in the download archive for more details and options***

+mksmith · March 31, 2022

Thanks @Trebor and @RevEng for the update to A7800! I know a lot of work has gone into this release so very much appreciate both of you hard work ???

+Propane13 · March 31, 2022

I know I could just try it myself to find out, but... can you tell us a bit more about the DMA usage per scanline feature?

RevEng · April 1, 2022

14 minutes ago, Propane13 said:

I know I could just try it myself to find out, but... can you tell us a bit more about the DMA usage per scanline feature?

I posted a screenshot of it with a brief explanation in the 7800 programming forum.

+TwentySixHundred · April 1, 2022

Yeah POKEY improvements are great, i tested with one of my bankswitch programs that didn't have any sound with v0.4. Works perfectly now. Really cool and makes me want to continue that project again.

Synthpopalooza · April 3, 2022

You've finally convinced me with this release, to throw away ProSystem emulator. So much better sounding.

However, for the near future I will continue cross-developing in Altirra then testing on the new A7800.

Edited April 3, 2022 by Synthpopalooza

A7800 - the Atari 7800 Emulator

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