Wait for VSYNC (VDU 23,0,&C3) not working?

[andrewmolyneux]

Platform: Windows 10 x64 Emulator version: v0.9.2 I've been playing with the emulator with a view to possibly buying a Console8. I wrote a BBC BASIC program to try scrolling the screen using VDU 23,7,m,d,z and I wanted it to be smooth so I added VDU 23,0,&C3 (flip buffer or wait for VSYNC) but it doesn't seem to be waiting for VSYNC. That is, I'd expect the program to take 8 seconds to scroll by a total of 480 pixels at 60 pixels per second, but it completes in well under a second. Have I misunderstood something or is the emulator not implementing the wait for VSYNC?

[andrewmolyneux]

Aha! I discovered *FX 19 is also supposed to wait for VSYNC and that works perfectly, so whatever's going on here presumably isn't an issue with the emulation. Ignore me 😀

[astralaster]

Did you use one of the double buffered modes? If not the swap buffer command might not do anything.

[andrewmolyneux]

I was working off the documentation here which says VDU 23, 0, &C3 “Flip(s) the screen buffer (double-buffered modes only) or wait(s) for VSYNC (all modes)" but I’ve found similar-looking pages elsewhere that don’t mention VSYNC so perhaps that page is just wrong 🤣

[andrewmolyneux]

Oh in fact @astralaster it seems that document is in your repo…

[astralaster]

I will check how it works on real hardware. But this might be a bug in the emulator.

[andrewmolyneux]

I guess if it works on real hardware we can reopen this 😄