> I feel noMMU might give better performance. I suppose this greatly depends on the chip available and the application you want to do.
Regarding the processor chip, with most brands the MMU and non-MMU chips will differ in much more than just the MMU-ness: different clock frequency, different memory interfaces and of course different price. I use the NIOS CPU (soft-core embedded in an Altera FPGA). Here I found that, while the maximum clock frequency allowable (and thus calculation speed) is not greatly affected, the average memory access seems to take about the double count of clock cycles (with cache enabled !). This might be caused partly by the fact that (other than with ARM) the cache seems to use physical addresses instead of virtual. But this is turn avoids the need to flush the cache with any task switch (that is what the ARM system does). So with many task switches the NIOS concept seems to be better, while the ARM concept might be faster with fewer task switches (and thus does appear better with DMIPS tests). Regarding software, the MMU does cost performance when tasks are switches (especially if cache flushing is necessary), but it might help to avoid some complexity in other areas. Within the FPGA, the MMU does introduce considerable additional coast in terms of needed gates and internal memory blocks. -Michael _______________________________________________ uClinux-dev mailing list uClinux-dev@uclinux.org http://mailman.uclinux.org/mailman/listinfo/uclinux-dev This message was resent by uclinux-dev@uclinux.org To unsubscribe see: http://mailman.uclinux.org/mailman/options/uclinux-dev
