If an exception occurs while a page-table walk is coincidentally in
progress (e.g., an illegal instruction executes during data TLB refill),
then the processor might enter M-mode. However, the PTW's accesses
should proceed without M privilege, to avoid bypassing PMPs.
Note, the same argument doesn't apply to the nonblocking cache's replay
queues, because those accesses have already been checked against the PMPs.
The cache correctly ignores access exceptions reported on replays,
provided no exceptions were reported on the initial access.
This one's a little invasive. To flush a specific entry from the TLB, you
need to reuse its CAM port. Since the TLB lookup can be on the critical
path, we wish to avoid muxing in another address.
This is simple on the data side, where the datapath already carries rs1 to
the TLB (it's the same path as the AMO address calculation). It's trickier
for the I$, where the TLB lookup address comes from the fetch stage PC.
The trick is to temporarily redirect the PC to rs1, then redirect the PC
again to the instruction after SFENCE.VMA.
Superpages create the possibility that two entries in the TLB may match.
This corresponds to a software bug, but we can't return complete garbage;
we must return either the old translation or the new translation. This
isn't compatible with the Mux1H approach. So, flush the TLB and report
a miss on duplicate entries.
This is simpler, reduces what would have become a critical path in
the commit stage, and will make it easier to support the mbadinst
CSR if it is implemented.
Fundamental new features:
* Added tile package: This package is intended to hold components re-usable across different types of tile. Will be the future location of TL2-RoCC accelerators and new diplomatic versions of intra-tile interfaces.
* Adopted [ModuleName]Params convention: Code base was very inconsistent about what to name case classes that provide parameters to modules. Settled on calling them [ModuleName]Params to distinguish them from config.Parameters and config.Config. So far applied mostly only to case classes defined within rocket and tile.
* Defined RocketTileParams: A nested case class containing case classes for all the components of a tile (L1 caches and core). Allows all such parameters to vary per-tile.
* Defined RocketCoreParams: All the parameters that can be varied per-core.
* Defined L1CacheParams: A trait defining the parameters common to L1 caches, made concrete in different derived case classes.
* Defined RocketTilesKey: A sequence of RocketTileParams, one for every tile to be created.
* Provided HeterogeneousDualCoreConfig: An example of making a heterogeneous chip with two cores, one big and one little.
* Changes to legacy code: ReplacementPolicy moved to package util. L1Metadata moved to package tile. Legacy L2 cache agent removed because it can no longer share the metadata array implementation with the L1. Legacy GroundTests on life support.
Additional changes that got rolled in along the way:
* rocket: Fix critical path through BTB for I$ index bits > pgIdxBits
* coreplex: tiles connected via :=*
* groundtest: updated to use TileParams
* tilelink: cache cork requirements are relaxed to allow more cacheless masters
