“They use just the instruction set and make their own microarchitecture.”
Is that really the case? My understanding is that while, yes, they make their own microarchitectures, they rely heavily on IP from ARM to make that happen
Do they write their own instruction decoders, FPUs, etc? I thought they started with the reference designs for a core and then tweaked them to their liking, some companies tweaking more than others
All of the main cores are ARM reference designs. Qualcomm does add proprietary IP, but it is more oriented around their strengths, like integrating their 5G modem into the die, which is something that none of the other big chip manufacturers can do at the moment (to my knowledge)
All of those companies except Amazon have shipped ARM CPU cores fully designed in-house, yes. But all except Apple and NVIDIA have since completely dropped their custom core design, and NVIDIA goes back and forth.
Qualcomm did buy Nuvia though, so they might yet come back with something new.
As uluyol corrected me, most of these seem to se ARM cores today. Few years back Samsung and Qualcomm had their own architectures. But the fact remains, if they have architecture license, ARM can't control them too much.
If they have an architecture license, they can make their own implementations of the ISA.
Certainly, they may choose to derive their implementations from ARM's designs (or use them wholesale), but the license allows them to make their own.
That said, in the mobile space, AIUI only Apple and ARM are nowadays developing their own implementations. In the HPC space, there are others (Fujitsu, Marvell, etc).
(ARM also sells more limited licenses which only allow their cores to be used.)
Is that really the case? My understanding is that while, yes, they make their own microarchitectures, they rely heavily on IP from ARM to make that happen
Do they write their own instruction decoders, FPUs, etc? I thought they started with the reference designs for a core and then tweaked them to their liking, some companies tweaking more than others
A peek inside Qualcomm’s upcoming chips, for example: https://www.anandtech.com/show/17091/qualcomm-announces-snap...
All of the main cores are ARM reference designs. Qualcomm does add proprietary IP, but it is more oriented around their strengths, like integrating their 5G modem into the die, which is something that none of the other big chip manufacturers can do at the moment (to my knowledge)