The original CSR registers ordering (big: MSB on lower addresses) is not convenient
when the SoC is interfaced with a real OS (for example as a PCIe add-on board or
with a CPU running Linux).
With this, the original ordering is kept as default (big), but it can now be switched
to little to avoid software workarounds in drivers and should probably be in the future
the default for PCIe/Linux SoCs.
This is needed to support memory regions up to 4GB in size (currently
limited to 2GB, or 0x8000_0000).
FIXME: CI complains about assertions re. axi_lite.address_width in
relationship to len(wishbone.adr) and wishbone_adr_shift, which
seems to be a problem on the 32bit (vexriscv?) CPU used for CI,
but seems to work fine on Rocket.
Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
foo
CSR write is only done if wishbone.sel != 0. This should avoid the need for 64-bit
CSR alignment on 64-bit CPUs since a 64-bit Wishbone write access targeting only the
32-bit LSB or MSB will be splitted in 2x32-bit accesses: one with sel=0xf, one with sel=0.
- do the CSR alignment update only if CPU is not CPUNone.
- revert PointToPoint interconnect when 1 master and 1 slave since this will
break others use cases and will prevent mapping slave to a specific location.
It's probably better to let the synthesis tools optimize the 1:1 mapping directly.
- add with_soc_interconnect parameter to add_sdram that defaults to True. When
set to False, only the LiteDRAMCore will be instantiated and interconnect with
the SoC will not be added.
This should also improve Wishbone timings.
Tested on iCEBreaker:
./icebreaker.py --cpu-type=None --uart-name=uartbone --csr-csv=csr.csv --build --flash
With the following script:
#!/usr/bin/env python3
import sys
from litex import RemoteClient
wb = RemoteClient()
wb.open()
# # #
print("scratch: 0x{:08x}".format(wb.regs.ctrl_scratch.read()))
errors = 0
for i in range(2):
for j in range(32):
wb.write(wb.mems.sram.base + 4*j, i + j)
for j in range(32):
if wb.read(wb.mems.sram.base + 4*j) != (i + j):
errors += 1
print("sram errors: {:d}".format(errors))
# # #
wb.close()
