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>
The current code has the possibility that we could set reg_addr
or reg_ctrl and then increment reg_addr in the same cycle, resulting
in some long timing paths. Rearrange the code to make it clear
that we are not trying to add an auto-increment to data from
outside the module; in any given cycle we either set one of
reg_addr and reg_ctrl, or we possibly increment reg_addr.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Since the condition setting got moved to writeback, execute2 does
nothing aside from wasting a cycle. This removes it.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This makes the exts[bhw] instructions do the sign extension in the
writeback stage using the sign-extension logic there instead of
having unique sign extension logic in execute1. This requires
passing the data length and sign extend flag from decode2 down
through execute1 and execute2 and into writeback. As a side bonus
we reduce the number of values in insn_type_t by two.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Benjamin Herrenschmidt
Michael Neuling
Paul Mackerras