"Emulate async read" parameter

[SWAT]

In DreamShell "none" param can be replaced by "true" if used optimized image (ISO or GDI) and IDE device.
If you plays with this value seems you are SD card user? For IDE devices just use DMA with "true async" and optimized images and it should works in most cases.
For SD device you can play with emu async value for more smooth gameplay if game load resources at gameplay. If not, use max value for faster loadings. It also auto disabled if game try load more than 100 sectors in one request, I detect it as "loading state" in game.
For some games better use lowest value, like Shenmue and Crazy taxi better use "1+" for emu async. Slow loadings, but smooth gameplay.

Emu async - is emulating DMA (it's works async) with PIO readings. It's split requested data reading for N sectors (this is emu async value is).
Lowest value - smooth gameplay, but slow loadings.
Highest value - lags in gameplay, but faster loadings.

For CDDA games just use highest value, because this games doesn't load resources at gameplay.

You can’t play some games on the SD card because it's only PIO device, the videos with lags, and it’s also more difficult with CDDA, so I would recommend getting an IDE mod and you forget about emu async and other limitations in most cases.