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3 Commits (b3b28044f85dab40252fec47ad3e4624dc58930f)

Author SHA1 Message Date
Benjamin Herrenschmidt 6aadad5a75 spi: Add booting from flash to litedram init 
It will look for an ELF binary at the flash offset specified
for the board (currently 0x300000 on Arty but that could be
changed).

Note: litedram is regenerated in order to rebuild the init code,
which was done using a newer version of litedram from LiteX.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Benjamin Herrenschmidt 573b6b4bc4 soc: Rework interconnect 
This changes the SoC interconnect such that the main 64-bit wishbone out
of the processor is first split between only 3 slaves (BRAM, DRAM and a
general "IO" bus) instead of all the slaves in the SoC.

The IO bus leg is then latched and down-converted to 32 bits data width,
before going through a second address decoder for the various IO devices.

This significantly reduces routing and timing pressure on the main bus,
allowing to get rid of frequent timing violations when synthetizing on
small'ish FPGAs such as the Artix-7 35T found on the original Arty board.

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