G1-ATA Devices

[SWAT]

I don't know why, I'm not have GDEMU for check it.
ISO images in from CD loader, are run almost directly, I'm just change LBA. Try images with a sector size more than 2048 (CDI or GDI with BIN tracks), they will be run with full syscall emulation, as in all other loaders with any formats.

The KallistiOS have support ISO9660 filesystem only with PIO reading for GD-ROM, so you can test speed only in PIO mode for now on GDEMU.

BTW, on settings page you change checkbox for DMA support or not? This may be a problem.
Maybe GDEMU works in PIO mode as in DMA (call interrupts or something). Try game that works in DMA now, for example DOA2, Sonic Adventure 2, Power Stone 2...