| DonFerrari said: Read again. PS4 BC on PS5 is as native as it can get when they put the logic of PS4 into the PS5 silicon. |
No, it's actually the other way around. PS5 silicon was designed keeping in mind it also has to play nice with PS4 silicon. Cerny (more or less casually) mentions this in his talk. AMD (and probably Sony watching over it) had to make sure that the "new transistors" don't run havoc when they see microcode intended for old PS4 hardware. This is a bit difficult to explain as it actually constitutes a huge engineering problem. (What AMD really did I have no clues at all).
As the naive solution, the PS5 could just kill half its CUs and lower the clocks to 800MHz on the gpu side and lower the cpu clocks to maybe 6-700MHz which makes it look like the new PS5 SoC executes with the same speed as the old PS4 SoC. This will not work in many cases as the timings in the new SoC would/could be completely different. If the PS5 runs too fast, all hell could break loose because the old PS4 code was not meant to run that fast (particularly code which used gpu cycles for async compute stuff on the PS4). In that context, the "dumbest PS4 game" is probably the safest bet for full bc, because it doesn't do tricks. My guess is it's the 1% of "tricky games" that constitute 99% of all headaches. Apparently within the 100 most popular games tested, the chosen solution seems to work for almost all of them out of the box.
