CompuServe Messages

Ariel, Well, as it turns out, there is an element of truth in both statements. You can indeedDMA directly into GVP's 32 bit memory, but they recommend against it. The reason for this is that the '030 has both an instruction and a data cache, (as opposed to the '020, which has only an instruction cache) and the problem arises from data changing in memory while the processor has that same data in its own cache. When the CPU has control of the data, it always knows when its cache is invalid, but external devices are a different matter. There are two ways around this. The first is to turn off the data cache (I don't know if you can turn it off separately from the instruction cache or not). The drawback to this method is that there is a considerable performance hit. The second method is to use the Mask parameter in the mountlist to exclude the 32 bit memory from DMA. This turns out (according to GVP) to be the best solution, since the processor is VERY fast, and programmed IO to 32 bit memory is as fast or faster than DMA to it (bearing in mind the limitations of the hard disk hardware). Take it for what it's worth. I would have to play with one for a while to see for myself. -larry