Such clock domains will "leak" into the enclosing scope, which is
generally undesirable. Also, this is instructive for a platform
overriding the behavior, since it provides guidance on how to
correctly instantiate platform-specific flops.
I've considered also doing this for MultiReg(), but it is very
challenging in presence of non-reset-less CDC FFs, since Yosys'
$dffsr primitive has separate set and clear inputs, and reshuffling
the reset value for those results in quite a bit of additional logic.
(That said, it might have to be done anyway, precisely because
letting Yosys generate this additional logic might prove too much
for the toolchain to cope with, and again, platform-independent
code should provide guidance to platform-specific code.)
This means that instead of:
with m.Case(0b00):
<body>
with m.Case(0b01):
<body>
it is legal to write:
with m.Case(0b00, 0b01):
<body>
with no change in semantics, and slightly nicer RTLIL or Verilog
output.
Fixes#103.
Do this to make sure all buffers, tristate/differential or not, are
instantiated the exact same way, and are subject to the same set of
toolchain bugs, if any.
Before this commit, in some cases there will be an inverter, which is
not allowed on an FDCE with IOB attribute set to true, as it will
interfere with packing.
This simplifies creation of related signals with nice names during
metaprogramming, e.g.
def make_ff(m, sig):
sig_ff = Signal.like(sig, name_suffix="_ff")
m.d.sync += sig_ff.eq(sig)
return sig_ff
This commit adds a best-effort error for a common mistake of adding
a clock driving the same domain twice, such as a result of
a copy-paste error.
Fixes#27.
The coercion is carefully chosen to accept (other than normal ints)
instances of e.g. np.int64, but reject instances of e.g. float.
See https://stackoverflow.com/a/48940855/254415 for details.
Fixes#93.
This adds the Clock() build DSL element, and adds a resource manager
function add_clock_constraint() that takes a Pin or a Signal.
Note that not all platforms, in particular not any nextpnr platforms
at the moment, can add constraints on arbitrary signals.
Fixes#86.
Right now the device name in the board file is just the option
nextpnr uses, but that's overnormalized and doesn't quite match
the chip names used elsewhere. It is even worse for ECP5 in terms
of mismatch with chip names, and for ECP5 we need to support other
toolchains as well, so let's handle this uniformly everywhere.
The iCE40 programmers are also moved, since they're board-specific.
(It looks like iceprog isn't, but it only works with Lattice
evaluation kits.)
Fixes#80.
This commit:
* moves lists of universally useful imports from `nmigen` to
`nmigen.hdl` and `nmigen.lib`, reimporting them in `nmigen`;
* replaces lots of imports from individual parts of `nmigen.hdl`
with a star import from `nmigen.hdl`;
* replaces imports in tests with what we expect downstream code
to use;
* adds some missing imports in `nmigen.formal`.
Although a dir="oe" pin is generally equivalent to dir="io" pin with
the i* signal(s) disconnected, they are not equivalent, because some
pins may not be able to support input buffers at all, either because
there are no input buffers, or because the input buffers are consumed
by some other resource.
E.g. this can happen on iCE40 when the input buffer is consumed by
a PLL.
Although a dir="oe" pin is generally equivalent to dir="io" pin with
the i* signal(s) disconnected, they are not equivalent, because some
pins may not be able to support input buffers at all, either because
there are no input buffers, or because the input buffers are consumed
by some other resource.
E.g. this can happen on iCE40 when the input buffer is consumed by
a PLL.
This provides an escape hatch for the case where the nMigen platform
code is not flexible enough, and a IO buffer primitive needs to be
instantiated directly.
This markedly differs from oMigen system, which would request
consecutive resources. The difference is deliberate; most resources
are singular, so it does not matter for them, and for resources where
it does matter, which pins are requested should not depend on order
of execution of `platform.request`.
This is necessary because on some platforms, like iCE40, extras
become parameters on an IO primitive, since the constraint file
format is not expressive enough for all of them.
In the simple cases, a Pin record consisting of exactly one field
is equivalent in every way to this single field. In the more complex
case however, it can be used as a record, making the code more robust
such that it works with both bidirectional and unidirectional pins.
