But can they both run at the same time?
We know that OG PS4 has an ARM CPU on the southbridge and 256MB of RAM. This processor gets activated in rest mode only.
Whenever the AMD APU is activated (i.e. PSN downloads), the ARM CPU is shut down. Am I getting this wrong?
My understanding is that you cannot have both running at the same time... it's one or the other.
Even the PS4 Pro which is more powerful (I assume the ARM CPU has been upgraded as well, since the southbridge RAM is 4 times larger) uses the APU to handle PSN downloads (you can hear the fan kicking in).
Sony had promised to fix this in a more powerful PS4, but they didn't, which is weird.
The ARM CPU seems to be fast enough to handle downloads:
https://fail0verflow.com/blog/2018/ps4-aeolia/
To sum it up, it seems that it's not possible to have an ARM CPU to handle OS functions while the game is running on the x86 CPU and thus having full access to 8 Ryzen cores.
I'd love to be wrong about it (who doesn't want more CPU horsepower for video games?), but I can still see Sony dedicating at least 1 Ryzen core for OS functions.
ps: That AMD project seems to be dead (not sure if it has anything to do with the ARM CPU on PS4).