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xilinx: Improve flip-flop handling.

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This adds support for infering more kinds of flip-flops:

- FFs with async set/reset and clock enable
- FFs with sync set/reset
- FFs with sync set/reset and clock enable

Some passes have been moved (and some added) in order for dff2dffs to
work correctly.

This gives us complete coverage of Virtex 6+ and Spartan 6 flip-flop
capabilities (though not latch capabilities).  Older FPGAs also support
having both a set and a reset input, which will be handled at a later
data.
This commit is contained in:
Marcin Kościelnicki 2019-11-21 06:30:06 +01:00 • committed by Marcin Kościelnicki
parent 22dd9f107c
commit aff6ad1ce0
8 changed files with 264 additions and 71 deletions
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15
techlibs/xilinx/synth_xilinx.cc
View file

@ -444,6 +444,16 @@ struct SynthXilinxPass : public ScriptPass
}
if (check_label("map_ffram")) {
// Required for dffsr2dff to work.
run("simplemap t:$dff t:$adff t:$mux");
// Needs to be done before opt -mux_bool happens.
run("dffsr2dff");
if (help_mode)
run("dff2dffs [-match-init]", "(-match-init for xc6s only)");
else if (family == "xc6s")
run("dff2dffs -match-init");
else
run("dff2dffs");
if (widemux > 0)
run("opt -fast -mux_bool -undriven -fine"); // Necessary to omit -mux_undef otherwise muxcover
// performs less efficiently
@ -453,14 +463,11 @@ struct SynthXilinxPass : public ScriptPass
}
if (check_label("fine")) {
run("dffsr2dff");
run("dff2dffe");
run("dff2dffe -direct-match $_DFF_* -direct-match $__DFFS_*");
if (help_mode) {
run("simplemap t:$mux", " ('-widemux' only)");
run("muxcover <internal options>, ('-widemux' only)");
}
else if (widemux > 0) {
run("simplemap t:$mux");
constexpr int cost_mux2 = 100;
std::string muxcover_args = stringf(" -nodecode -mux2=%d", cost_mux2);
switch (widemux) {