Consecutive accesses from the same master shouldn't need an IDLE
cycle. Completely remove the IDLE state and switch master when
the bus is idle, but stay on the last selected one between cycles.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Stores only need a single cycle, so we can ack them early if there
isn't an older ack already in the pipeline
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This replaces the simple_ram_behavioural and mw_soc_memory modules
with a common wishbone_bram_wrapper.vhdl that interfaces the
pipelined WB with a lower-level RAM module, along with an FPGA
and a sim variants of the latter.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This adds an output buffer to help with timing and allows the BRAMs
to actually pipeline.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Vivado by default tries to flatten the module hierarchy to improve
placement and timing. However this makes debugging timing issues
really hard as the net names in the timing report can be pretty
bogus.
This adds a generic that can be used to control attributes to stop
vivado from flattening the main core components. The resulting design
will have worst timing overall but it will be easier to understand
what the worst timing path are and address them.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
The CR update currently depends on the complete data formatting
mux chain. This makes it source its inputs from a bit earlier in
the chian, thus improving timing a bit
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This doesn't yet pipeline the block RAM, just generate a valid stall
signal so it's compatible with a pipelined master
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
The generic PIPELINE_DEPTH can be set to 0 to keep it operating
as a non-pipelined slave, or a larger value indicating
the amount of extra cycles between requests and acks.
It will always generate a valid stall signal, so it can be used
in either mode with a pipelined master (but only in non-pipelined
mode with a non-pipelined master).
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
For now ... it reduces the routing pressure on the FPGA
This needs manual adjustment of the address decoder in soc.vhdl, at
least until I can figure out how to deal with std_match
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
# Conflicts:
# soc.vhdl
# Conflicts:
# soc.vhdl
All that needs to be changed now is the size in wishbone_types.vhdl
and the address decoder in soc.vhdl
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
We don't yet have a proper snooper for the icache, so for now make
icbi just flush the whole thing
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
The instruction works by redirecting fetch to nia+4 (hopefully using
the same adder used to generate LR) and doing a backflush. Along with
being single issue, this should guarantee that the next instruction
only gets fetched after the pipe's been emptied.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
We used the variable "way" in the wrong state in the cache when
updating a line valid bit after the end of the wishbone transactions,
we need to use the latched "store_way".
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Clearly separate the 2 stages of load hits, improve naming and
comments, clarify the writeback controls etc...
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Adding lines seems to add only little extra as the BRAMs aren't
full, 2 ways is our current comprimise to limit pressure on small
FPGAs. We could go to 64 lines for a little more, but timing is
becoming a bit too right to my linking on the tags/LRU path of
the icache, so let's leave it at 32 for now.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This makes the BRAMs use an output buffer, introducing an extra
cycle latency. Without this, Vivado won't make timing at 100Mhz.
We stash all the necessary response data in delayed latches, the
extra cycle is NOT a state in the state machine, thus it's fully
pipelined and doesn't involve stalling.
This introduces an extra non-pipelined cycle for loads with update
to avoid collision on the writeback output between the now delayed
load data and the register update. We could avoid it by moving
the register update in the pipeline bubble created by the extra
update state, but it's a bit trickier, so I leave that for a latter
optimization.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This replaces loadstore2 with a dcache
The dcache unit is losely based on the icache one (same basic cache
layout), but has some significant logic additions to deal with stores,
loads with update, non-cachable accesses and other differences due to
operating in the execution part of the pipeline rather than the fetch
part.
The cache is store-through, though a hit with an existing line will
update the line rather than invalidate it.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This might slightly increase the logic in synthesis but avoids
us looking at uninitialized tags when not servicing an active
request
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Few tweaks based on a newcomers experience getting an Arty A7-100 up and running
Forgot to add DCO in initial PR, now corrected.
Signed-off-by: Hugh Blemings <hugh@blemings.org>
The icache_test.bin file was missing. This adds it (along with a python3
script to generate it).
We also add better reporting on errors
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Initialize to 0 forces the mux to have an extra leg fed with zeros.
Instead initialize data_in to one of the mux inputs
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Benjamin Herrenschmidt
Michael Neuling
Paul Mackerras