Commit Graph

8 Commits (d2ca625b3b9c98de607b2a56f8428c70ab343891)

Author SHA1 Message Date
Benjamin Herrenschmidt d415e5544a fetch/icache: Fit icache in BRAM
The goal is to have the icache fit in BRAM by latching the output
into a register. In order to avoid timing issues , we need to give
the BRAM a full cycle on reads, and thus we souce the BRAM address
directly from fetch1 latched NIA.

(Note: This will be problematic if/when we want to hash the address,
we'll probably be better off having fetch1 latch a fully hashed address
along with the normal one, so the icache can use the former to address
the BRAM and pass the latter along)

One difficulty is that we cannot really stall the icache without adding
more combo logic that would break the "one full cycle" BRAM model. This
means that on stalls from decode, by the time we stall fetch1, it has
already gone to the next address, which the icache is already latching.

We work around this by having a "stash" buffer in fetch2 that will stash
away the icache output on a stall, and override the output of the icache
with the content of the stash buffer when unstalling.

This requires a rewrite of the stop/step debug logic as well. We now
do most of the hard work in fetch1 which makes more sense.

Note: Vivado is still not inferring an built-in output register for the
BRAMs. I don't want to add another cycle... I don't fully understand why
it wouldn't be able to treat current_row as such but clearly it won't. At
least the timing seems good enough now for 100Mhz, possibly more.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 3589f92d5a fetch1: Simplify a bit
There is no need to have two different state records

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 8af2b004c3 Simplify fetch1
Do the +4 in a single place. This shouldn't cause any difference
in behaviour as these are sequential variable assignments.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 3a6fcc09d4 Reformat fetch1
No code change

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 98f0994698 Add core debug module
This module adds some simple core controls:

  reset, stop, start, step

along with icache clear and reading the NIA and core
status bits

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org
5 years ago
Anton Blanchard d52046104f Add a default value for RESET_ADDRESS
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Anton Blanchard 92a7152370 Rework pipeline, add stall and flush signals
This adds stall and flush signals to the pipeline.

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago
Anton Blanchard 5a29cb4699 Initial import of microwatt
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
5 years ago