allenjbaum
commented
2 years ago Sorry to have to pile on here. I think you're too close to this, so you're not explaining things that are obvious to you. This doc says: Part of the socket standard is the fact that the root CS exists at 0x3000. Which socket standard is this? IS this a proposed platform spec standard? This doc doesn't actually say that mconfigptr is a CSR - that should be clear.
From this example I think that there is
- some kind of ROM on the motherboard (at address 0x3000) that points back to each daughtercard, and
- another on each daughtercard that points to a ROM on each socket, and that contains the CS for that socket (it could be inside the socket, or external). At least, that's how I interpret it (while acknowledging my superpower of finding a different explanation for whatever someone describes). Since I would expect that all sockets could be identical, that means that - at the socket, the address decoding would be ignoring bits 21:20 (assuming 2 daughter cards), and bits 17:16 when routing to the ROM.
Alternately, there could be a ROM on the motherboard that contains all of the CSes, and it ignores all irrelevant address bits to keep it small.
But, in the former case: what happens when someone tries to follow the breadcrumbs to some socket, and that socket isn't even plugged in? (a bus error?). In the latter case: the ROM is accessible - but the socket isn't populated. How is that discovered?
timsifive
Also slight reorganisation to (hopefully) make more sense.