The instruction set is not as critical as you might think, and ARM has the huge advantage of a lot of working implementations which you can already buy.
Semiconductor design teams don't exactly grow on trees, either. It was over a decade from Apple buying PA Semi whole (https://en.wikipedia.org/wiki/P.A._Semi ) to announcing the M1.
And of course if you're going to do that you already need the rest of the vertically integrated pipeline to build motherboards to put your chips on, peripheral IP to do all the other things other than processing, etc.
I would think USB would be more of a OS issue, though. If a USB driver came as a blob, my Talos II obviously couldn't run it, but otherwise pretty much all USB stuff just works if I have source code for it (Fedora). Page size can ruin your day for some devices -- I have to hack FireWire, for example, because it assumes a 4K page size and Fedora uses 64K pages -- but so far no issues with USB or AMD GPUs.
Optimization is a bigger issue, though autovectorization in compilers is making it less of a problem than it used to be, as well as us nerd pioneers getting things upstreamed.
Although it's one of the "different" things, along with memory model, the page size is the same for Fedora aarch64 if I remember the discussion right.
Is POWER9 compilation generally poor compared with other targets? It didn't seem so to me, apart from a pathological case on one benchmark set which IBM addressed swiftly. They've been supporting GCC for rather a long time.
That used to be the case until https://www.spinics.net/linux/fedora/fedora-kernel/msg12805.... which put aarch64 to 4K. I argue there should be a workstation ppc64le spin that does this, but I understand why Fedora doesn't want to put the releng resources towards a niche audience.
I agree IBM's autovector stuff is quite good in gcc but there's no substitute for hand-rolled assembly sometimes.
Quite. I can't think of any reason other than retrocomputing that someone would want an OpenSPARC.
I think people forget that the economies are different with hardware vs software; because you cannot eradicate the per-unit cost of hardware, paying a small part of that in license fees is not a big deal, especially since it comes with integration support that saves you a lot of non-recurring R&D expense. Whereas in software, being free makes it zero-friction and this has a huge impact on adoption.
Semiconductor design teams don't exactly grow on trees, either. It was over a decade from Apple buying PA Semi whole (https://en.wikipedia.org/wiki/P.A._Semi ) to announcing the M1.
And of course if you're going to do that you already need the rest of the vertically integrated pipeline to build motherboards to put your chips on, peripheral IP to do all the other things other than processing, etc.