FCEUX PPU timing issue

FCEUX PPU timing issue
by Eugene.S on 2016-10-05 (#180509)

Real hardware and accurate emulators, like mesen/punes/nintendulator/nestopia
shows this timing roms values exactly as this screenshots:

Tepples overclock demo ROM
240pee, cpu speed

But cycles/line and cpu speed shows a bit lower values on FCEUX.
RockNES and BizHawk had same issue, but it's fixed for now.

Zepper wrote:

"Probably the test ROM uses sprite zero hit, or overflow, to measure the timing. The only change was to avoid the sprites to evaluate on pre-render scanline."

Is this sprite evaluation bug?

Re: FCEUX PPU timing issue
by tepples on 2016-10-05 (#180523)

Yes.

The overclock test measures time between sprite overflow and sprite 0 in CPU cycles. Because FCEUX's sprite evaluation timing isn't perfect, the time between sprite overflow and sprite 0 differs from the authentic PPU.

Re: FCEUX PPU timing issue
by Zepper on 2016-10-05 (#180524)

@Eugene.S
Care to provide the link of my quoted post? I'm not finding it.

Re: FCEUX PPU timing issue
by Eugene.S on 2016-10-06 (#180539)

Zepper, it's here:

BTW, i've posted it to bugtracker, but really doubt anyone fix it.
Which games (in theory) may be affected by this bug?
Or this bug manifest only on timing roms, so don't need care about fix it?

Re: FCEUX PPU timing issue
by Zepper on 2016-10-06 (#180545)

Oh, it was a private message. :shock: