It turns out the Chisel C++ backend can't emit correct initialization
code for a 128 bit wide NastiROM. Rather than trying to fix Chisel, I'm
just going to hack up the backup memory port Verilog harness a bit more
to make it work.
Note that the backup memory port Verilog already couldn't take arbitrary
parameters for MIF_*, so it's not like we're losing any flexibility
here.
The backup memory port doesn't work on multi-channel configurations, it
just screws up the Nasti tag bits. This patch always instantiates a
single-channel backup memory port, which relies on the memory channel
selector to only enable a single memory channel when the backup memory
port is enabled. There are some assertions to make sure this happens,
as otherwise memory gets silently corrupted.
While this is a bit of a hack, the backup memory port will be going away
soon so I don't want to spend a whole lot of time fixing it. The
generated hardware is actually very similar: we used to elaborate a
Nasti arbiter inside the backup memory support, now there's one outside
of it instead.
We need this to work for our chip, and it's not been tested in a long
time in upstream -- it didn't even used to build since the Nasti
conversion. This makes a few changes:
* Rather than calling the backup memory port parameters MEM_*, it calls
them MIF_* (to match the MIT* paramater objects). A new name was
necessary because the Nasti stuff is now dumped as MEM_*, which has
similar names but incompatible values.
* p(MIFDataBits) was changed back to 128, as otherwise the backup
memory port doesn't work (it only send half a TileLink transaction).
64 also causes readmemh to bail out, but changing the elf2hex parameters
works around that.
* A configuration was added that enabled the backup memory port in the
tester. While this is kind of an awkward way to do it, I want to
make sure I can start testing this regularly and this makes it easy to
integrate.
We used to just be writing the SCR anyway, but now that the SCR maps are
automatically defined VCS will detect the missing SCR and bail out when
compiling test harness code. This patch just doesn't write the HTIF SCR when
there isn't one.
We're building a chip with 8 memory channels. Since this will require a
complicated test setup we want to also be able to bring up the chip with fewer
memory channels. This commit adds a SCR that controls the number of active
memory channels on a chip. Toggling this SCR will scramble memory and drop
Nasti messages, so it's only possible to change while the chip is booting.
By default this just adds a 1-bit SCR, which essentially no extra logic.
When multiple memory channel configurations are enabled at elaboration time, a
NastiMemoryInterconnect is generated for each channel configuration. The
number of outstanding misses is increased to coorespond to the maximum number
of banks per memory channel (added as a parameter), which I believe is
necessary to avoid deadlock in the memory system.
A configuration is added that supports 8 memory channels but has only 1 enabled
by default.
This uses the new SCRFile changes to generate a header file containing a list
of all the SCRs in a core to remove the magic constant "63" (the HTIF clock
divider control register) and replace it with a generated number (which is
still 63).
