22 Mar 2016 16:01
|wawa t wrote:|
| i have heard there is a penalty in access to ram when using higher resolutions an probably deeper color modes, because the rtg and the main ram is using the same bus in parallel. the higher the amount of memory needs to be accessed at refresh the higher the penalty. |
is that the case?
Yes, it is. The vampire has a unified memory approach just like the original Amiga. The main difference is that the RAM of the vampire is very fast when compared to the Amiga's chipmem.
| i heard the suggestion to use different/opposite flanks of the clock signal to trigger access main ram (fast?) and rtg ram (chip? vram?), which would virtually decouple bot kind of ram access from each other without the need of using higher frequencies, which is impossible i guess.|
Regardless of how it would be done, one could, of course, add "fastmem" to the vampire, i.e. RAM that is exclusive to the CPU. However, it will have much less effect on the overall performance than with a classic Amiga which is mainly due to the CPU caches (meaning that the CPU can live without memory in many situations) and the relatively lower fraction of mem bandwidth taken by the screen DMA. Hence, it is not really worth it. It would be much better to use the same approach (extra pins or higher transfer clock or whatever) to make the unified RAM faster.