CTL's idea of "HAL" is ridiculously overrated. For "HAL" read "PCI Interface". It's not a whole HAL for the OS. Way, way from it. There's a whole shedload of ways to accelerate RISC OS anyway - a simple hook in to the horizontal line-draw routine primitive (which I believe ViewFinder may do??) will accelerate all PLOT and Draw module operations massively. Same for sprites - you just write a new module that provides the same API but talks to your accelerated hardware. Don't underestimate how modular RISC OS already is in many areas!