clock_enable version has worse sound in some games

[sorgelig]

Listen the "Street of Rage 2" title song. In old jt12 version that percussion sound is perfect. In new version it's has high "hiss" instead of and lost its original a-la cymbals sound.

[sorgelig]

it turned out this famous phinc_VI

reg [19:0] phinc_VI; // expanded to 20-bit widht, as per @ElectronAsh's advice

if i change it to 16, then it start to sound as before. So, i'm confusing by this. 20 bits look correct but 17bits sounds better.

[jotego]

I don't hear a difference with 16/20 bits change. Maybe the culprit is different.

[sorgelig]

In messenger you told opposite. So do you hear or not?

[jotego]

Now that we have fixed the timers (and other things) do you still hear problems related to phinc_VI? Note that is is sized as [19:0] in the #28 commit.

[gyurco]

Just tried with the latest version: https://github.com/jotego/jt12/commit/4741953a0b27b1f89a82c0be057839ba3effdda7 Golden Axe, Afterburner are very bad. Music is recognizable, but with very strange instruments. Percussion is just some hissing noise.

This is the jt12 instantiation in the fpgagen version I'm using: https://github.com/gyurco/fpgagen/blob/90391948dc2df65fe7bf401fe329cf7f1400a04d/src/virtual_toplevel.vhd#L784

Strange, after loading something which has proper music, then loading e.g. Golden Axe again, it has better music (but still with some wrong instruments).

[gyurco]

Load Lemmings, start the game, allow the music to start, then load Golden Axe, and it is much better then :) But still sounds worse than the old.

[gyurco]

The version from MiSTer with the FIFO is ok however. Seems an SCFIFO would be enough there.

[jotego]

I don't want to add the FIFO to the code because it deviates from original hardware in a fundamental level. FIFO is required because of different system-level timing of FPGAgen with respect to real Megadrive. @sorgelig is it easy to move the FIFO out of JT12?

[sorgelig]

Yes, it's possible. I plan to do this later.

[gyurco]

I've implemented an external FIFO, but didn't solve the problem. Then I checked other changes in MiSTer Alexey's repo (hehe), and found out that the opram initialization is guilty. So using ram[x] = { ~7'd0, 37'd0 }; solves the bad sounds in MiST, too. Unfortunatlely I don't know how to implement it correctly for Xilinx. The app note says use ISE 13.2 or 18k RAM type.

[sorgelig]

FIFO is moved out of jt12

[jotego]

clock_enable branch is now better than master. Merged in release 0.4