Commit Graph

18 Commits (c0c00d05bc6adc2223d00222262002c811f360c4)

Author SHA1 Message Date
Raptor Engineering Development Team fcb783a0fb Extend LiteDRAM VHDL wrapper to allow more than one clock line
This is necessary for the upcoming Arctic Tern system enablement,
since Arctic Tern uses two DRAM devices and a separate clock line
is routed to each device.  LiteX handles this behavior correctly,
therefore we assume other hardware exists that uses a similar
DRAM clock design.

Updates from Mikey to fix some compile issues.

Signed-off-by: Timothy Pearson <tpearson@raptorengineering.com>
Signed-off-by: Michael Neuling <mikey@neuling.org>
3 years ago
Paul Mackerras ca4eb46aea Make wishbone addresses be in units of doublewords or words
This makes the 64-bit wishbone buses have the address expressed in
units of doublewords (64 bits), and similarly for the 32-bit buses the
address is in units of words (32 bits).  This is to comply with the
wishbone spec.  Previously the addresses on the wishbone buses were in
units of bytes regardless of the bus data width, which is not correct
and caused problems with interfacing with externally-generated logic.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
3 years ago
Benjamin Herrenschmidt bedc9c0085 litedram: l2: Add a few comments about litedram behaviour
litedram ignores a couple of signals of his "pseudo-axi" port,
this adds a bit of documentation around it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt 02abb135a8 litedram: l2: Add support for more geometries
Make the DRAM data lines and user port width configurable, also
don't hard wire dependency on the wishbone data width.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt 1441b2a859 litedram: l2: Latency improvements
This implements in the L2 cache the feature already in the L1s
allowing a request to be completed before the end of a refill
using partial line valid bits, and starting a refill from the
row of the first miss on that line instead of the beginning of
the line.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt 15467fe536 litedram: L2 use latched refill_index
Not a huge difference since wb_req is itself a latch but
may as well

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt 05bbbf0772 litedram: Pipeline store acks in L2
There is a long timing path to generate the ack signal from
the L2 cache as it's fully combinational for stores, including
signals coming from litedram.

Instead, pipeline the store acks. This will introduce a cycle
latency but should improve timing. Also the core will eventually
be smart enough not to wait for store acks to complete them anyway.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt b58ff724f6 litedram: Add stash buffer to the L2 cache wishbone interface
This breaks the long stall signal coming back to the processor
and helps improve overall timing.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt b23fd6c5f1 litedram: Defer clearing of tags & valids to improve timing
Currently, there's a huge mux gathering the output of all the PLRUs
to select the victim way on cache miss. This is fed combinationally
into the clearing of the valid and tags.

In order to help timing, let's store it instead and perform the
clearing on the next cycle. The L2 doesn't respond to requests
when not in IDLE state so this should have no negative effects.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt a93d9e77c9 litedram: Remove remnants of riscv-inits
We still had some wires bringing an extra serial port out of
litedram for the built-in riscv processor. This is all gone now
so take them out.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt b0e15f2fb5 litedram: Make the L2 twice as tall
This increases the number of L2 lines from 32 to 64. The BRAM usage is the
same as they were only half used. There's an increase in LUTs and registers
due to the extra tags and valid bits, but none of it should be in a
space constrained or critical timing path.

We could make it wider instead (256 bytes lines) which would reduce usage
instead, but this increases the latency by 8 cycles. Something to consider
once the L2 is capable of early response on miss and starting reloads
from any point in a line.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt 599fad117b litedram: Remove old "VexRiscV" based initializations
Support for this has bitrotted and would require refactoring of L2 to
be brought back. It's also not really needed anymore now that we ship
pre-generated litedram and that LiteX supports what we do.

So take it out, which simplifies some of the scripts as well. This also
fixes up CSR alignment the sim model.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt 6828e93113 litedram: Test bench
The test bench test simple access forms for now, it's a starting point
but it already helped find/fix a bug.

Includes a litedram update to be able to operate the sim model without
inits.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt a3857aac94 litedram: Add an L2 cache with store queue
This adds a cache between the wishbone and litedram with the following
features (at this point, it's still evolving)

  - 128 bytes line width in order to have a reasonable amount of
litedram pipelining on the 128-bit wide data port.

  - Configurable geometry otherwise

  - Stores are acked immediately on wishbone whether hit or miss
(minus a 2 cycles delay if there's a previous load response in the
way) and sent to LiteDRAM via 8 entries (configurable) store queue

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt bf1b98b958 litedram: Add support for booting without BRAM
This adds an option to disable the main BRAM and instead copy a
payload stashed along with the init code in the secondary BRAM
into DRAM and boot from there

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt 6fe077910b litedram: Add simulation support
This adds a simulated litedram model along with the necessary
Makefile gunk to verilate it and wrap it for use by ghdl.

The core_dram_tb test bench is a variant of core_tb with
LiteDRAM simulated. It's not built by default, an explicit

make core_dram_tb

is necessary as to not require verilator to be installed for
the normal build process (also it's slow'ish).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
4 years ago
Benjamin Herrenschmidt 12f36b4a35 litedram: Split the init memory from the main wrapper
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago
Benjamin Herrenschmidt 982cf166dd litedram: Add basic support for LiteX LiteDRAM
This comes in two parts:

 - A generator script which uses LiteX to generate litedram cores
along with their init files for various boards (currently Arty and
Nexys-video). This comes with configs for arty and nexys_video.

 - A fusesoc "generator" which uses pre-generated litedram cores

The generation process is manual on purpose. This include pre-generated
cores for the two above boards.

This is done so that one doesn't have to install LiteX to build
microwatt. In addition, the generator script or wrapper vhdl tend to
break when LiteX changes significantly which happens.

This is still rather standalone and hasn't been plumbed into the SoC
or the FPGA toplevel files yet.

At this point LiteDRAM self-initializes using a built-in VexRiscv
"Minimum" core obtained from LiteX and included in this commit. There
is some plumbing to generate and cores that are initialized by Microwatt
directly but this isn't working yet and so isn't enabled yet.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
5 years ago