OOOOK, so, some news. Got it almost working !
Here is my tutorial, maybe it can help someone
hardware : W7, UMSA (must work w/ vga to scart cable too), ATi R7 240 1go pcie card, LCD display, CRT display
- install CRTemudriver (read geedorah website to know exactly how)
- if you have 2 screens (my setup : LCD screen attached to the dvi or hdmi, CRT on VGA), make sure on the W7 display panel that CRT is marked as your main display
- launch VMM (included in CRTemudrivers). import this set of modelines (hope these are the good ones, let me know otherwise) : https://www.studio-digi.com/super_custom.ini
uncheck extended display, and make sure the import is made in "STATIC’ (screenshot at the end of this tutorial)
- generate modelines, install modelines. The CRT screen should flick one second, this means the operation was sucessful.
- launch arcade_OSD (also packed w/ CRTemudrivers), and check that 15khz resolutions are available. Make sur to you selected “attach OSD to current monitor” to have the good values.
- get retroarch latest release. unpack. launch once, close. If needed use my retroarch cfg file : https://www.studio-digi.com/retroarch.cfg
- if all work as expected (or, like it worked for me), you should get retroarch with the RGUI interface (not the PS3ish one), fullscreen, at the right resolution.
- go to ui interface, check if the advanced mode is activated
- go to video, then CRTswitch, put it in 15khz mode, 2560, custom freshrate activated.
- now try some emulators, they should almost all work ! (some are not in my case, like 3DO - black screen, Wii/GC works but the gamepad is not, and some other small bugs). Exiting a game or retroarch can sometime break the screen resolution (CTRL alt del + task manager to get off this situation)
Thank you @Alphanu for your incredible work, it’s so amazing to have saturn, DC, megadrive, snes so beautifuly displayed, as we just plugged the real thing on the TV.
Hope this tutorial will help people like me. If it doesn’t work let me know, maybe I missed a step or the custom res file is not the good one (made so many tests…)