ElBrunzy wrote on 2021-05-06, 04:08:
Hi OPLx, I'm preparing my computer to receive the SAAYM. I'm so glad it's happening and soon I'll be able to listen to my favorite arcade music on original hardware thanks to the SAAYM and SBVGM, I can barely believe it! The card has a bit more onboard configuration than I expected, I did some research and found a great documentation TexElec wrote which proved being very helpful but I wanted to have your advice on the card setup since SBVGM will be it's main usage, maybe I'll try to run some CMS game on it.
I'm pretty sure SBVGM dont use YM2151's IRQ, I read that some arcade board might use it for some reason, am I right to assume SBVGM does not ? I'm less certain about IO ChRdy for the SAA1099, but since it seem to be conflict-free I'll leave it on, do you have anything to say about it ? IO port 210h seem like a nice default so I'll leave it here. From the card literature I think it's a no brainer for me to let the SAA1099 clock to it's default 7.16mhz settings, but the text is less clear about the other synth. Since for me the YM2151 is the pièce de résistance of the card and I have everything to learn about it I would highly appreciate to know what you think about that 3.58mhz/4mhz switch.
SBVGM doesn't use any of the YM2151's IRQs. The IRQs were generally used by the arcade machine (or computer) that ran the game. Most cases this IRQ was used for the music playback interrupt. I'm still not sure what IO ChRdy triggers on the PC (I need to find out more one of these days), but SBVGM doesn't use this either.
The reason why there are two clock settings is because the SAAYM was keeping in mind the Commander X16 which originally was going to have one YM2151 (at 4MHz), one SAA1099 (at 8MHz), and a VERA (an FPGA) that handles sound (and other operations). The recent specification for the Commander X16 has removed the SAA1099 since VERA's sound can more or less do what the SAA1099 does.
Depending on what you want to do, you can leave the SAAYM at address 210h. That way any software that uses the Game Blaster or Creative Music System cards will find it. I would also leave the clock setting for the YM2151 at 3.58MHz. SBVGM assumes that this is the clock speed that the YM2151 is running at.
Depending on how your system is set up, you can leave the IRQ at 5 and the IO ChRdy jumpers connected. From my tests the YM2151 on the SAAYM does correctly trigger the IRQ it's been configured for. I hope there will be more software for the SAAYM since the YM2151 is a pretty nice FM chip and having the YM2151's internal timers available for use opens up some interesting things on PC.