Konami's K054539 chip is a PCM sound generator with digital signal processing (DSP) features. You have already seen it in three JT cores compatible with Konami's X-Men, Premier Soccer, and Run and Gun. This chip is not well understood and there is no faithful emulation available for it. Furrtek has published schematics for it, but it is a large chip and hard to understand.
The first beta for Premier Soccer came out with a lot of sound problems. The beta for Run'n Gun was a bit better, but if you played long enough you could eventually run into some noise. There were also some incorrect sounds in the X-Men game.
After 2 or 3 weeks working on it, I have been able to integrate some of the findings from Furrtek's schematics into my jt539 sound module. Now these three games have much better sound, without going into noise loops or playing wrong samples. One of the most interesting features implemented is routing a secondary sound chip through the K054539. This auxiliary input can be connected either to Yamaha chips, using Yamaha encoding, or to a general raw 16-bit stereo sound. Because the chip applies additional gain to the auxiliary signal internally, doing this correctly means that the balance of the different instruments and sound effects becomes correct. Other features that are now implemented correctly are stereo pan effects—including the disabling bit—and the different types of PCM encoding. All these enhancements are not available in emulation as of today.
There is one big aspect still missing, though: DSP effects. These seem to come in two flavours. They can use an external RAM memory, probably to implement echo effects. They can also work without it by feeding back the previous output, maybe for some sort of IIR filter. This is the most obscure feature of the chip and the biggest difference with real hardware at the moment. We will continue working on it, so stay tuned!
Other Updates
Apart from the JT539 sound chip work, the Neo Geo Pocket has got the focus with the new year. We are working on enabling game saves. This is actually needed in order to be able to finish some games, so it is an important feature. As game saves are not common on arcade games, we do not have experience setting this up and we need to learn a lot about how MiSTer and Analogue Pocket deal with this. This work will take another 1–2 weeks to have it ready on MiSTer and then probably another week to have it ready on the Analogue Pocket. Bear with us.
After making the CPU required for Caliber 50, the next item needed in that core is the PCM chip. One much easier than the K054539, though!
The CPS cores still need a bit of re-architecting to guarantee accurate speed under all conditions. This work will require about 1–2 weeks of effort and it may only affect a couple of games, but because this core is very important to the gaming scene we will do it.
About CPS3, I am still at the architecture design step, so I still cannot share anything concrete. The work done for Run'n Gun shows important limits of the SDRAM architecture of the MiSTer. Similarly, the issue I mentioned about CPS accuracy is related to SDRAM congestion too. So I am a bit worried about whether everything will run nicely or not. I need to explore this further.
Thanks to your continuous support, we have decided to hire a new team member to help with schematic extraction. This is a fundamental part of development and has brought up a lot of unknown features in games in the past. It is quite expensive, though, as converting a single PCB may take a full month. We always publish our schematics, so your funding is helping the preservation of actual hardware in the long run too.
Thanks!