Text flickering on Gaiares titelscreen

[Former user]

Original [issue 134](https://code.google.com/p/genplus-gx/issues/detail?id=134) created by gora.patrick on 2010-11-06T07:10:06.000Z:

What steps will reproduce the problem? boot up the game Gaiares and wait for the titescreen to appear

What is the expected output? What do you see instead? titlescreen with non flickering text

What version of the emulator are you using (official, SVN revision,...)? 1.40

Please provide any additional information below (Video settings, Console region,...) 480p, PAL machine

[Former user]

Comment # 1 originally posted by ekeeke31 on 2010-11-06T10:49:28.000Z:

Indeed, just tested on real hardware and it does not flicker like that (well, for me, only the bottom text is flickering in genesis plus, the rest is fine).

[Former user]

Comment # 2 originally posted by gora.patrick on 2010-11-06T11:06:24.000Z:

yeah, only the bottom text is flickering for me as well, not the whole screen.

[Former user]

Comment # 3 originally posted by ekeeke31 on 2010-11-06T17:09:21.000Z:

Ok, I figured this one. This is a little bit technical so it's only for those interested in Genesis emulation, really.

It happens in any emulators that does not handle DMA access line-by-line (as on real hardware). When a DMA is triggered, most emulators perform all the writes immediately then lock the CPU during the DMA access time. On real hardware, only a fixed number of writes is allowed per line of display so the writes are not done "immediately".

This works fine as most games does not do DMA during active display and when they do, they do not try to modify the active display with the DMA writes.

This game however does this: every 10-12 frames, it clears the plane that holds the text bottom area then fill it again, using two consecutive DMA operation. This is their method used for displaying the blinking "Press START" text. However, the first DMA is triggered during active display and if you process all the writes immediately, the bottom text will not be displayed. On real hardware, the writes that clears the bottom area are delayed and would actually be processed AFTER this area has been displayed, so you don't get any flickering.

I knew I was not emulated it accurately but as now game seemed to require igt, I left that for later. I guess it's time to improve the accuracy level again, let's hope it does not break any games.

[Former user]

Comment # 4 originally posted by ekeeke31 on 2010-12-04T17:24:30.000Z: