Audio Fixes

Development Update

Work still keeps us busy towards the two next big cores: Run'n Gun and CPS3, with these stepping stones

• Add Golfing Greats to JTRIDERS, as it uses the same pseudo 3D chip as Run'n Gun but without a frame buffer

• Fix frame buffer on OutRun for Analogue Pocket users

• 3D chip plus working frame buffer leads to Run'n Gun

• Frame buffer is a requisite for CPS3

As we moved forward with Golfing Greats, including fixing a critical audio problem in MAME, we realised that compared to Run'n Gun, the pseudo 3D chip takes considerably more SDRAM bandwidth. For each pixel on the screen, the chip requires two SDRAM reads carrying a total of 4 bytes. This is due to the tile map being too large to reside inside the FPGA -as it does on Run'n Gun- so it has to stay in the SDRAM. But then the problem is that memory cannot perform at the required speed and only half of the screen gets drawn!

We shifted to a compression mechanism of the tile map data on the fly, so we can reduce it from 1.2MByte to just 128kB while keeping the random access capability. At that size, it can be moved into the FPGA solving the memory speed problem. We are currently working on the implementation of this architecture.

The Run'n Gun core now has working audio and needs the frame buffer as the next step. So attention shifted back to the OutRun problem on Analogue Pocket devices. Some Pocket machines won't display the sprites. This has been an on-and-off problem hard to debug and I had put it off a while ago as it only affected one core. If we are going to need this feature for three cores (Outrun, Run'n Gun and CPS3) it becomes much more relevant. So I resumed working on it. I have discovered some weak points on the current implementation and I distributed some files which the community gracefully tested. But, more work is needed.

Audio Fixes

There were some audio issues noticed by users which I fixed recently. So we have a file update today. These are the fixes:

• Audio was breaking up on Ajax

• Stereo audio implemented on Ajax

• Tora michi PCM sound was too low

• Circus Charlie applause was distorted

Ajax stereo audio is interesting because the schematics show how the left/right panning is achieved but the two channels eventually get merged into a mono amplifier driving a single speaker. So there must be another PCB version where a stereo amplifier is used. The game does use stereo sound effects, at least on the airplane scenes.

Thank you for your support,
JT