Original code by Chris Weber 1998 (Aminet). Updated and enhanced by SpeedGeek 2015.
A2091ToFast copies the A2091/A590 ROM code into Fast memory similar to the CPU FastROM command but does not require an MMU. This allows it to work with many other CPUs which don't have an MMU or free the MMU to perform other tasks. More importantly, it can speed up the execution of the SCSI driver code by SEVERAL HUNDRED percent!
Note: Zorro2 Fast memory and Zorro2 ROMs operate at the same bus speed so there is no benefit to using A2091ToFast on a "Bog Standard" 7 MHz 68000. However, unlike the Zorro2 ROMs the Zorro2 Fast memory can be cached so the L2 cache on some 68000 accelerators (or the L1 cache on 68020+ accelerators) may still realize some benefit.
I've uploaded RSCP images showing PIO speed on my system is now a little faster than original DMA speed (and much faster than ROM based PIO speed). Enjoy!
P.S. If I were AndyLandy I would not be surprised it's possible to squeeze a few more drops of performance from our trusty old C= SCSI controllers!
P.P.S. Another thread will posted on EAB to satisfy non-Amibay member download issues.