Before this commit, it was possible to set and get clock constraints
placed on Pin objects. This was not a very good implementation, since
it relied on matching the identity of the provided Pin object to
a previously requested one. The only reason it worked like that is
deficiencies in nextpnr.
Since then, nextpnr has been fixed to allow setting constraints on
arbitrary nets. Correspondingly, backends that are using Synplify
were changed to use [get_nets] instead of [get_ports] in SDC files.
However, in some situations, Synplify does not allow specifying
ports in [get_nets]. (In fact, nextpnr had a similar problem, but
it has also been fixed.)
The simplest way to address this is to refer to the interior net
(after the input buffer), which always works. The only downside
of this is that requesting a clock as a raw pin using
platform.request("clk", dir="-")
and directly applying a constraint to it could fail in some cases.
This is not a significant issue.
Because of YosysHQ/yosys#1390, using a transparent port in AsyncFIFO,
instead of being a no-op (as the semantics of \TRANSPARENT would
require it to be in this case), results in a failure to infer BRAM.
This can be easily avoided by using a non-transparent port instead,
which produces the desirable result with Yosys. It does not affect
the semantics on Xilinx platforms, since the interaction between
the two ports in case of address collision is undefined in either
transparent (WRITE_FIRST) or non-transparent (READ_FIRST) case, and
the data out of the write port is not used at all.
Fixes#172.
This is necessary for consistency, since for transparent read ports,
we currently do not support .en at all (it is fixed at 1) due to
YosysHQ/yosys#760. Before this commit, changing port transparency
would require adding or removing an assignment to .en, which is
confusing and error-prone.
Also, most read ports are always enabled, so this behavior is also
convenient.
Also, replace `bits, sign = x.shape()` with more idiomatic
`width, signed = x.shape()`.
This unifies all properties corresponding to `len(x)` to `x.width`.
(Not all values have a `width` property.)
Fixes#210.
It's not practical to detect tools within the toolchain environment
for various reasons, so just assume the tools are there if the user
says they are.
Before this commit, the tools would be searched outside the toolchain
environment, which of course would always fail for Vivado, ISE, etc.
This obscure functionality was likely only ever used in old MiSoC
code, and doesn't justify the added complexity. It was also not
provided (and could not be reasonably provided) in SyncFIFOBuffered,
which made its utility extremely marginal.
