Snes9x4d for Miyoo

Snes9x4d for MiyooCFW devices. Should run in both BittBoy and PocketGo, however it is only tested on PocketGo v1.

Usage

Assuming that you're using the latest version of MiyooCFW, go to the releases tab and download the latest version of snes9x4d file. Put this file in sd://emus/snes9x4d, substituting the file that is in there. That's it!

To check if you're running the latest version, open the emulator and press R button to open menu, and check the title. It should be written something like Snes9x4d vYYYY.MM.DD for Miyoo (where YYYY.MM.DD is a date).

Optional: You can overclock your device to either 732MHz or 798MHz to get better performance. To do this press Select when SNES is selected in Emulators menu, select EDIT SNES and adjust CPU Clock to either 702 (default), 732 or 798. Not all devices support all overclock options, so if your device freeze reduce the overclock or return to default.

Options

This emulator has multiple options that can be accessed using Reset button in BittBoy/PocketGo. They may improve performance at the expense of quality. Some of them are described below:

• Transparency (default True): enables/disables transparency effects in games. Disabling it may improve performance, but it may also break some effects in games and even make some of them unplayable because of missing effects
• Full Screen (default False): enables/disables full screen. There is a small performance impact for it, and it also makes the aspect ratio wrong
• Billinear Filtering (default False): enables/disables bilinear filtering. Only makes sense when Full Screen is also True. This makes the image in full screen smoother at the expense of performance
• Frameskip (default Auto): sets frameskipping. It works by skipping some frames, for example assuming a NTSC (USA or Japanese) ROM with 60Hz of refresh rate, setting Frameskip to 60/2 will skip every other frame (rendering only 30 frames per second instead of 60). Auto tries to skip frames as much as necessary to keep full speed
• Auto Frameskip (default Max. 3): defines the maximum frames to skip when Frameskip is set to Auto. You can increase it to allow the game to render faster, at the expense of more stuttering and input lag. My recommendation is to not use a value bigger than Max. 4. For games that need fast reaction times you may want to decrease this value
• Sound Rate (default 32000): sets sound rate. The official sound rate of SNES is ~32000 so this is the minimum recommended value to have a good sound quality, but you may reduce it to improve performance. You can also disable sound by setting this option to off
• Stereo (default False): enables/disables stereo mixing. Disabling it improves performance, but the Mono mixing results in some missing instruments in games

My personal performance tip is to disable Stereo and Transparency. This makes the most performance gains in games where those options doesn't break anything.

Setting Frameskip to Auto is the only current way to have a framerate limit, so it is recommended to always use it. You can adjust the maximum number of frames to skip using Auto Frameskip option. Still, Auto Frameskip does bring some overhead so it may make sense to use fixed Frameskip values sometimes, but keep it in mind that the game can go too fast in areas where there is little going on (for example, game menus).

If you want to play with Sound Rate, 22050 still gives a very good sound, but in my experience it doesn't improve performance that much. 16000 is acceptable and anything below it is better to simply disable sound (that gives much better performance gains).

Setup environment

First, you need to setup a toolchain. This code is tested with:

• https://github.com/steward-fu/miyoo/
• https://github.com/bittboy/buildroot/

The first one is easier to setup since it has some instructions and also the toolchain is pre-built, but it is also based on an older version of GCC (7.3.0) using uclibc.

The second one needs to be compiled from source, but is based on a much newer version of GCC (10.1.0) and also uses musl, a newer implementation of C stdlib.

Assuming that you're going to use https://github.com/bittboy/buildroot/, the first step is to have a Linux environment setup. I used a Debian 9 VM for this.

The only necessary package outside the minimal setup is build-essential and git, so install it first:

$ sudo apt install build-essential git

Afterwards, clone https://github.com/bittboy/buildroot/, and run:

$ cd buildroot
$ make

This will take a while and may need some retries (for example, I had to run make three times to finish the build). After building the toolchain, you should have a output inside buildroot directory.

You need to add the cross-compilers to your PATH. So run:

# In buildroot directory
$ export PATH=$PWD/output/host/bin:$PATH

Bulding

After setting up your environment, run:

$ make

It will generate a binary snes9x4d binary. You can them substitute sd://emus/snes9x4d contents with the ones in the generated directory.

You can build this binary using PGO. To do this, first:

$ make PGO=GENERATE

To generate a binary with instrumentation. Put this in your Miyoo and play a little, but keep in mind that a PGO binary is very slow (so be patient, it is worth it). Afterwards, copy profile directory from sd://emus/snes9x4d to the root of the project and run:

$ make PGO=APPLY

To apply optimizations. A profile.zip file is included with each release with a playthrough of some game, but it may not be updated with master branch. Also, keep in mind that if you want the best performance in your specific game it may be better to generate your playthrough of it.

Porting

While this fork removes support for any other device outside Miyoo (since I don't have the infrastructure to maintain the ports), it should be straightforward to port this code for a new device, specially for a Dingux-like (Linux+SDL) devices.

Each specific device feature is behind compiler-flags so it shouldn't affect compilation for other targets. This port has many code clean-ups, so it should be easier to navigate compared to other snes9x4d ports. Also this port brings some additional optimizations and features not available in other snes9x4d ports, like the color operations code from Snes9x 1.60, bilinear(ish) filtering from PocketSNES, LAGFIX from snes9x2002, etc.

Some tips to port this project to another Dingoo-like device:

• You can start by getting your toolchain working and creating a new Makefile for your device (just make a copy of the original one and change some things)
• Enable/disable some compile toggles (see CCFLAGS in Makefile) according to your device. Some of the compile toggles are described below:
  • SPC700_SHUTDOWN is a speed hack available from Snes9x itself, so it should be safe to enable.
  • FAST_LSB_WORD_ACCESS seems to speed-up the code access to some memory operations. Recommended if your target supports it
  • FAST_ALIGNED_LSB_WORD_ACCESS is a similar to above, but only optimizes aligned memory access. If your target doesn't support the above, this one may work
  • VIDEO_MODE defines some configuration related to video. For now there are 3 pre-defined video modes: 1 for 320x240, 2 for 400x240 and 3 for 480x272. If your device has another resolution, you will need to define a new video mode (check src/sdlmenu/sdlvideo.h file) and a new scaler function (see src/sdlmenu/scaler.cpp)
  • BILINEAR_SCALE is an alternative scale method that has higher quality than the default one (it is slightly more expansive too). For now, it is only available for VIDEO_MODE=1, so if your device uses any other video mode it is better to disable it
  • MIYOO is obviously used only for Miyoo devices, so you shouldn't define it for your own device. But looking where it is used in the code should help you to define your own device-specific code
  • C4_OLD (this is a Makefile flag) use an older version of C(x)4 chip emulation that uses approximations. Probably faster but more inaccurate. Cx4 chip was only used in 2 games: Mega Man X 2 and 3
  • LAGFIX this flag reduces the input lag in one frame (~16ms). Backported from snes9x2002, and you can read more about it here: https://www.libretro.com/index.php/core-progress-snes9x-2002-input-lag-reduced-by-1-2-frames/
  • SNESADVANCE_SPEEDHACKS enables some speedhacks that can be loaded by a special crafted snesadvanced.dat file (there is an example in this repository). Just put this file in ~/.snes9x4d-ng/snesadvanced.dat and load a ROM, if there is an available speedhack it will be automatically applied. My own testing is inconclusive if this brings any benefit in speed, though
• If your device is like Miyoo and doesn't have an standard Dingoo layout, you should define your own custom layout by creating a file src/sdlmenu/<device>.h and mapping the SDL buttons accordingly (see src/sdlmenu/miyoo.h for an example). Afterwards, just import your custom mapping conditionally in src/sdlmenu/sdlmain.cpp and it should work