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Merge pull request #1438 from YosysHQ/eddie/xilinx_dsp_comments

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Add notes and comments for xilinx_dsp
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Eddie Hung 2019-10-08 10:53:30 -07:00 • committed by GitHub
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14
passes/pmgen/xilinx_dsp.cc
View file

@ -609,8 +609,13 @@ struct XilinxDspPass : public Pass {
extra_args(args, argidx, design);
for (auto module : design->selected_modules()) {
// Experimental feature: pack $add/$sub cells with
// (* use_dsp48="simd" *) into DSP48E1's using its
// SIMD feature
xilinx_simd_pack(module, module->selected_cells());
// Match for all features ([ABDMP][12]?REG, pre-adder,
// post-adder, pattern detector, etc.) except for CREG
{
xilinx_dsp_pm pm(module, module->selected_cells());
pm.run_xilinx_dsp_pack(xilinx_dsp_pack);
@ -619,14 +624,17 @@ struct XilinxDspPass : public Pass {
// is no guarantee that the cell ordering corresponds
// to the "expected" case (i.e. the order in which
// they appear in the source) thus the possiblity
// existed that a register got packed as CREG into a
// existed that a register got packed as a CREG into a
// downstream DSP that should have otherwise been a
// PREG of an upstream DSP that had not been pattern
// matched yet
// PREG of an upstream DSP that had not been visited
// yet
{
xilinx_dsp_CREG_pm pm(module, module->selected_cells());
pm.run_xilinx_dsp_packC(xilinx_dsp_packC);
}
// Lastly, identify and utilise PCOUT -> PCIN,
// ACOUT -> ACIN, and BCOUT-> BCIN dedicated cascade
// chains
{
xilinx_dsp_cascade_pm pm(module, module->selected_cells());
pm.run_xilinx_dsp_cascade();

188
passes/pmgen/xilinx_dsp.pmg
View file

@ -1,3 +1,57 @@
// This file describes the main pattern matcher setup (of three total) that
// forms the `xilinx_dsp` pass described in xilinx_dsp.cc
// At a high level, it works as follows:
// ( 1) Starting from a DSP48E1 cell
// ( 2) Match the driver of the 'A' input to a possible $dff cell (ADREG)
// (attached to at most two $mux cells that implement clock-enable or
// reset functionality, using a subpattern discussed below)
// If ADREG matched, treat 'A' input as input of ADREG
// ( 3) Match the driver of the 'A' and 'D' inputs for a possible $add cell
// (pre-adder)
// ( 4) If pre-adder was present, find match 'A' input for A2REG
// If pre-adder was not present, move ADREG to A2REG
// If A2REG, then match 'A' input for A1REG
// ( 5) Match 'B' input for B2REG
// If B2REG, then match 'B' input for B1REG
// ( 6) Match 'D' input for DREG
// ( 7) Match 'P' output that exclusively drives an MREG
// ( 8) Match 'P' output that exclusively drives one of two inputs to an $add
// cell (post-adder).
// The other input to the adder is assumed to come in from the 'C' input
// (note: 'P' -> 'C' connections that exist for accumulators are
// recognised in xilinx_dsp.cc).
// ( 9) Match 'P' output that exclusively drives a PREG
// (10) If post-adder and PREG both present, match for a $mux cell driving
// the 'C' input, where one of the $mux's inputs is the PREG output.
// This indicates an accumulator situation, and one where a $mux exists
// to override the accumulated value:
// +--------------------------------+
// | ____ |
// +--| \ |
// |$mux|-+ |
// 'C' ---|____/ | |
// | /-------\ +----+ |
// +----+ +-| post- |___|PREG|---+ 'P'
// |MREG|------ | adder | +----+
// +----+ \-------/
// (11) If PREG present, match for a greater-than-or-equal $ge cell attached
// to the 'P' output where it is compared to a constant that is a
// power-of-2: e.g. `assign overflow = (PREG >= 2**40);`
// In this scenario, the pattern detector functionality of a DSP48E1 can
// to implement this function
// Notes:
// - The intention of this pattern matcher is for it to be compatible with
// DSP48E1 cells inferred from multiply operations by Yosys, as well as for
// user instantiations that may already contain the cells being packed...
// (though the latter is currently untested)
// - Since the $dff-with-optional-clock-enable-or-reset-mux pattern is used
// for each *REG match, it has been factored out into two subpatterns:
// in_dffe and out_dffe located at the bottom of this file.
// - Matching for pattern detector features is currently incomplete. For
// example, matching for underflow as well as overflow detection is
// possible, as would auto-reset, enabling saturated arithmetic, detecting
// custom patterns, etc.
pattern xilinx_dsp_pack
state <SigBit> clock
@ -5,12 +59,11 @@ state <SigSpec> sigA sigB sigC sigD sigM sigP
state <IdString> postAddAB postAddMuxAB
state <bool> ffA1cepol ffA2cepol ffADcepol ffB1cepol ffB2cepol ffDcepol ffMcepol ffPcepol
state <bool> ffArstpol ffADrstpol ffBrstpol ffDrstpol ffMrstpol ffPrstpol
state <Cell*> ffAD ffADcemux ffADrstmux ffA1 ffA1cemux ffA1rstmux ffA2 ffA2cemux ffA2rstmux
state <Cell*> ffB1 ffB1cemux ffB1rstmux ffB2 ffB2cemux ffB2rstmux
state <Cell*> ffD ffDcemux ffDrstmux ffM ffMcemux ffMrstmux ffP ffPcemux ffPrstmux
// subpattern
// Variables used for subpatterns
state <SigSpec> argQ argD
state <bool> ffcepol ffrstpol
state <int> ffoffset
@ -19,6 +72,7 @@ udata <SigBit> dffclock
udata <Cell*> dff dffcemux dffrstmux
udata <bool> dffcepol dffrstpol
// (1) Starting from a DSP48E1 cell
match dsp
select dsp->type.in(\DSP48E1)
endmatch
@ -50,17 +104,21 @@ code sigA sigB sigC sigD sigM clock
sigM.append(P[i]);
}
log_assert(nusers(P.extract_end(i)) <= 1);
// This sigM could have no users if downstream sinks (e.g. $add) is
// narrower than $mul result, for example
if (sigM.empty())
reject;
}
else
sigM = P;
// This sigM could have no users if downstream $add
// is narrower than $mul result, for example
if (sigM.empty())
reject;
clock = port(dsp, \CLK, SigBit());
endcode
// (2) Match the driver of the 'A' input to a possible $dff cell (ADREG)
// (attached to at most two $mux cells that implement clock-enable or
// reset functionality, using a subpattern discussed above)
// If matched, treat 'A' input as input of ADREG
code argQ ffAD ffADcemux ffADrstmux ffADcepol ffADrstpol sigA clock
if (param(dsp, \ADREG).as_int() == 0) {
argQ = sigA;
@ -81,6 +139,8 @@ code argQ ffAD ffADcemux ffADrstmux ffADcepol ffADrstpol sigA clock
}
endcode
// (3) Match the driver of the 'A' and 'D' inputs for a possible $add cell
// (pre-adder)
match preAdd
if sigD.empty() || sigD.is_fully_zero()
// Ensure that preAdder not already used
@ -106,11 +166,12 @@ code sigA sigD
if (preAdd) {
sigA = port(preAdd, \A);
sigD = port(preAdd, \B);
if (GetSize(sigA) < GetSize(sigD))
std::swap(sigA, sigD);
}
endcode
// (4) If pre-adder was present, find match 'A' input for A2REG
// If pre-adder was not present, move ADREG to A2REG
// Then match 'A' input for A1REG
code argQ ffAD ffADcemux ffADrstmux ffADcepol ffADrstpol sigA clock ffA2 ffA2cemux ffA2rstmux ffA2cepol ffArstpol ffA1 ffA1cemux ffA1rstmux ffA1cepol
// Only search for ffA2 if there was a pre-adder
// (otherwise ffA2 would have been matched as ffAD)
@ -173,6 +234,8 @@ ffA1_end: ;
}
endcode
// (5) Match 'B' input for B2REG
// If B2REG, then match 'B' input for B1REG
code argQ ffB2 ffB2cemux ffB2rstmux ffB2cepol ffBrstpol sigB clock ffB1 ffB1cemux ffB1rstmux ffB1cepol
if (param(dsp, \BREG).as_int() == 0) {
argQ = sigB;
@ -222,6 +285,7 @@ ffB1_end: ;
}
endcode
// (6) Match 'D' input for DREG
code argQ ffD ffDcemux ffDrstmux ffDcepol ffDrstpol sigD clock
if (param(dsp, \DREG).as_int() == 0) {
argQ = sigD;
@ -242,6 +306,7 @@ code argQ ffD ffDcemux ffDrstmux ffDcepol ffDrstpol sigD clock
}
endcode
// (7) Match 'P' output that exclusively drives an MREG
code argD ffM ffMcemux ffMrstmux ffMcepol ffMrstpol sigM sigP clock
if (param(dsp, \MREG).as_int() == 0 && nusers(sigM) == 2) {
argD = sigM;
@ -263,6 +328,11 @@ code argD ffM ffMcemux ffMrstmux ffMcepol ffMrstpol sigM sigP clock
sigP = sigM;
endcode
// (8) Match 'P' output that exclusively drives one of two inputs to an $add
// cell (post-adder).
// The other input to the adder is assumed to come in from the 'C' input
// (note: 'P' -> 'C' connections that exist for accumulators are
// recognised in xilinx_dsp.cc).
match postAdd
// Ensure that Z mux is not already used
if port(dsp, \OPMODE, SigSpec()).extract(4,3).is_fully_zero()
@ -291,6 +361,7 @@ code sigC sigP
}
endcode
// (9) Match 'P' output that exclusively drives a PREG
code argD ffP ffPcemux ffPrstmux ffPcepol ffPrstpol sigP clock
if (param(dsp, \PREG).as_int() == 0) {
int users = 2;
@ -316,6 +387,19 @@ code argD ffP ffPcemux ffPrstmux ffPcepol ffPrstpol sigP clock
}
endcode
// (10) If post-adder and PREG both present, match for a $mux cell driving
// the 'C' input, where one of the $mux's inputs is the PREG output.
// This indicates an accumulator situation, and one where a $mux exists
// to override the accumulated value:
// +--------------------------------+
// | ____ |
// +--| \ |
// |$mux|-+ |
// 'C' ---|____/ | |
// | /-------\ +----+ |
// +----+ +-| post- |___|PREG|---+ 'P'
// |MREG|------ | adder | +----+
// +----+ \-------/
match postAddMux
if postAdd
if ffP
@ -333,6 +417,11 @@ code sigC
sigC = port(postAddMux, postAddMuxAB == \A ? \B : \A);
endcode
// (11) If PREG present, match for a greater-than-or-equal $ge cell attached to
// the 'P' output where it is compared to a constant that is a power-of-2:
// e.g. `assign overflow = (PREG >= 2**40);`
// In this scenario, the pattern detector functionality of a DSP48E1 can
// to implement this function
match overflow
if ffP
if param(dsp, \USE_PATTERN_DETECT, Const("NO_PATDET")).decode_string() == "NO_PATDET"
@ -351,22 +440,45 @@ endcode
// #######################
// Subpattern for matching against input registers, based on knowledge of the
// 'Q' input. Typically, identifying registers with clock-enable and reset
// capability would be a task would be handled by other Yosys passes such as
// dff2dffe, but since DSP inference happens much before this, these patterns
// have to be manually identified.
// At a high level:
// (1) Starting from a $dff cell that (partially or fully) drives the given
// 'Q' argument
// (2) Match for a $mux cell implementing synchronous reset semantics ---
// one that exclusively drives the 'D' input of the $dff, with one of its
// $mux inputs being fully zero
// (3) Match for a $mux cell implement clock enable semantics --- one that
// exclusively drives the 'D' input of the $dff (or the other input of
// the reset $mux) and where one of this $mux's inputs is connected to
// the 'Q' output of the $dff
subpattern in_dffe
arg argD argQ clock
code
dff = nullptr;
for (auto c : argQ.chunks()) {
for (const auto &c : argQ.chunks()) {
// Abandon matches when 'Q' is a constant
if (!c.wire)
reject;
// Abandon matches when 'Q' has the keep attribute set
if (c.wire->get_bool_attribute(\keep))
reject;
Const init = c.wire->attributes.at(\init, State::Sx);
if (!init.is_fully_undef() && !init.is_fully_zero())
// Abandon matches when 'Q' has a non-zero init attribute set
// (not supported by DSP48E1)
Const init = c.wire->attributes.at(\init, Const());
if (!init.empty())
for (auto b : init.extract(c.offset, c.width))
if (b != State::Sx && b != State::S0)
reject;
}
endcode
// (1) Starting from a $dff cell that (partially or fully) drives the given
// 'Q' argument
match ff
select ff->type.in($dff)
// DSP48E1 does not support clock inversion
@ -379,14 +491,12 @@ match ff
filter GetSize(port(ff, \Q)) >= offset + GetSize(argQ)
filter port(ff, \Q).extract(offset, GetSize(argQ)) == argQ
filter clock == SigBit() || port(ff, \CLK) == clock
set ffoffset offset
endmatch
code argQ argD
{
if (clock != SigBit() && port(ff, \CLK) != clock)
reject;
SigSpec Q = port(ff, \Q);
dff = ff;
dffclock = port(ff, \CLK);
@ -398,9 +508,11 @@ code argQ argD
// has two (ff, ffrstmux) users
if (nusers(dffD) > 2)
argD = SigSpec();
}
endcode
// (2) Match for a $mux cell implementing synchronous reset semantics ---
// exclusively drives the 'D' input of the $dff, with one of the $mux
// inputs being fully zero
match ffrstmux
if !argD.empty()
select ffrstmux->type.in($mux)
@ -432,6 +544,10 @@ code argD
dffrstmux = nullptr;
endcode
// (3) Match for a $mux cell implement clock enable semantics --- one that
// exclusively drives the 'D' input of the $dff (or the other input of
// the reset $mux) and where one of this $mux's inputs is connected to
// the 'Q' output of the $dff
match ffcemux
if !argD.empty()
select ffcemux->type.in($mux)
@ -456,16 +572,32 @@ endcode
// #######################
// Subpattern for matching against output registers, based on knowledge of the
// 'D' input.
// At a high level:
// (1) Starting from an optional $mux cell that implements clock enable
// semantics --- one where the given 'D' argument (partially or fully)
// drives one of its two inputs
// (2) Starting from, or continuing onto, another optional $mux cell that
// implements synchronous reset semantics --- one where the given 'D'
// argument (or the clock enable $mux output) drives one of its two inputs
// and where the other input is fully zero
// (3) Match for a $dff cell (whose 'D' input is the 'D' argument, or the
// output of the previous clock enable or reset $mux cells)
subpattern out_dffe
arg argD argQ clock
code
dff = nullptr;
for (auto c : argD.chunks())
// Abandon matches when 'D' has the keep attribute set
if (c.wire->get_bool_attribute(\keep))
reject;
endcode
// (1) Starting from an optional $mux cell that implements clock enable
// semantics --- one where the given 'D' argument (partially or fully)
// drives one of its two inputs
match ffcemux
select ffcemux->type.in($mux)
// ffcemux output must have two users: ffcemux and ff.D
@ -504,6 +636,10 @@ code argD argQ
}
endcode
// (2) Starting from, or continuing onto, another optional $mux cell that
// implements synchronous reset semantics --- one where the given 'D'
// argument (or the clock enable $mux output) drives one of its two inputs
// and where the other input is fully zero
match ffrstmux
select ffrstmux->type.in($mux)
// ffrstmux output must have two users: ffrstmux and ff.D
@ -542,6 +678,8 @@ code argD argQ
}
endcode
// (3) Match for a $dff cell (whose 'D' input is the 'D' argument, or the
// output of the previous clock enable or reset $mux cells)
match ff
select ff->type.in($dff)
// DSP48E1 does not support clock inversion
@ -558,14 +696,12 @@ match ff
// Check that FF.Q is connected to CE-mux
filter !ffcemux || port(ff, \Q).extract(offset, GetSize(argQ)) == argQ
filter clock == SigBit() || port(ff, \CLK) == clock
set ffoffset offset
endmatch
code argQ
if (ff) {
if (clock != SigBit() && port(ff, \CLK) != clock)
reject;
SigSpec D = port(ff, \D);
SigSpec Q = port(ff, \Q);
if (!ffcemux) {
@ -573,17 +709,17 @@ code argQ
argQ.replace(D, Q);
}
// Abandon matches when 'Q' has a non-zero init attribute set
// (not supported by DSP48E1)
for (auto c : argQ.chunks()) {
Const init = c.wire->attributes.at(\init, State::Sx);
if (!init.is_fully_undef() && !init.is_fully_zero())
Const init = c.wire->attributes.at(\init, Const());
if (!init.empty())
for (auto b : init.extract(c.offset, c.width))
if (b != State::Sx && b != State::S0)
reject;
}
dff = ff;
dffQ = argQ;
dffclock = port(ff, \CLK);
}
// No enable/reset mux possible without flop
else if (dffcemux || dffrstmux)
reject;
endcode

79
passes/pmgen/xilinx_dsp_CREG.pmg
View file

@ -1,3 +1,26 @@
// This file describes the second of three pattern matcher setups that
// forms the `xilinx_dsp` pass described in xilinx_dsp.cc
// At a high level, it works as follows:
// (1) Starting from a DSP48E1 cell that (a) doesn't have a CREG already,
// and (b) uses the 'C' port
// (2) Match the driver of the 'C' input to a possible $dff cell (CREG)
// (attached to at most two $mux cells that implement clock-enable or
// reset functionality, using a subpattern discussed below)
// Notes:
// - Running CREG packing after xilinx_dsp_pack is necessary since there is no
// guarantee that the cell ordering corresponds to the "expected" case (i.e.
// the order in which they appear in the source) thus the possiblity existed
// that a register got packed as a CREG into a downstream DSP that should
// have otherwise been a PREG of an upstream DSP that had not been visited
// yet
// - The reason this is separated out from the xilinx_dsp.pmg file is
// for efficiency --- each *.pmg file creates a class of the same basename,
// which when constructed, creates a custom database tailored to the
// pattern(s) contained within. Since the pattern in this file must be
// executed after the pattern contained in xilinx_dsp.pmg, it is necessary
// to reconstruct this database. Separating the two patterns into
// independent files causes two smaller, more specific, databases.
pattern xilinx_dsp_packC
udata <std::function<SigSpec(const SigSpec&)>> unextend
@ -6,7 +29,7 @@ state <SigSpec> sigC sigP
state <bool> ffCcepol ffCrstpol
state <Cell*> ffC ffCcemux ffCrstmux
// subpattern
// Variables used for subpatterns
state <SigSpec> argQ argD
state <bool> ffcepol ffrstpol
state <int> ffoffset
@ -15,13 +38,15 @@ udata <SigBit> dffclock
udata <Cell*> dff dffcemux dffrstmux
udata <bool> dffcepol dffrstpol
// (1) Starting from a DSP48E1 cell that (a) doesn't have a CREG already,
// and (b) uses the 'C' port
match dsp
select dsp->type.in(\DSP48E1)
select param(dsp, \CREG, 1).as_int() == 0
select nusers(port(dsp, \C, SigSpec())) > 1
endmatch
code argQ ffC ffCcemux ffCrstmux ffCcepol ffCrstpol sigC sigP clock
code sigC sigP clock
unextend = [](const SigSpec &sig) {
int i;
for (i = GetSize(sig)-1; i > 0; i--)
@ -48,11 +73,13 @@ code argQ ffC ffCcemux ffCrstmux ffCcepol ffCrstpol sigC sigP clock
else
sigP = P;
if (sigC == sigP)
reject;
clock = port(dsp, \CLK, SigBit());
endcode
// (2) Match the driver of the 'C' input to a possible $dff cell (CREG)
// (attached to at most two $mux cells that implement clock-enable or
// reset functionality, using the in_dffe subpattern)
code argQ ffC ffCcemux ffCrstmux ffCcepol ffCrstpol sigC clock
argQ = sigC;
subpattern(in_dffe);
if (dff) {
@ -77,22 +104,44 @@ endcode
// #######################
// Subpattern for matching against input registers, based on knowledge of the
// 'Q' input. Typically, identifying registers with clock-enable and reset
// capability would be a task would be handled by other Yosys passes such as
// dff2dffe, but since DSP inference happens much before this, these patterns
// have to be manually identified.
// At a high level:
// (1) Starting from a $dff cell that (partially or fully) drives the given
// 'Q' argument
// (2) Match for a $mux cell implementing synchronous reset semantics ---
// one that exclusively drives the 'D' input of the $dff, with one of its
// $mux inputs being fully zero
// (3) Match for a $mux cell implement clock enable semantics --- one that
// exclusively drives the 'D' input of the $dff (or the other input of
// the reset $mux) and where one of this $mux's inputs is connected to
// the 'Q' output of the $dff
subpattern in_dffe
arg argD argQ clock
code
dff = nullptr;
for (auto c : argQ.chunks()) {
for (const auto &c : argQ.chunks()) {
// Abandon matches when 'Q' is a constant
if (!c.wire)
reject;
// Abandon matches when 'Q' has the keep attribute set
if (c.wire->get_bool_attribute(\keep))
reject;
Const init = c.wire->attributes.at(\init, State::Sx);
if (!init.is_fully_undef() && !init.is_fully_zero())
// Abandon matches when 'Q' has a non-zero init attribute set
// (not supported by DSP48E1)
Const init = c.wire->attributes.at(\init, Const());
for (auto b : init.extract(c.offset, c.width))
if (b != State::Sx && b != State::S0)
reject;
}
endcode
// (1) Starting from a $dff cell that (partially or fully) drives the given
// 'Q' argument
match ff
select ff->type.in($dff)
// DSP48E1 does not support clock inversion
@ -105,14 +154,12 @@ match ff
filter GetSize(port(ff, \Q)) >= offset + GetSize(argQ)
filter port(ff, \Q).extract(offset, GetSize(argQ)) == argQ
filter clock == SigBit() || port(ff, \CLK) == clock
set ffoffset offset
endmatch
code argQ argD
{
if (clock != SigBit() && port(ff, \CLK) != clock)
reject;
SigSpec Q = port(ff, \Q);
dff = ff;
dffclock = port(ff, \CLK);
@ -124,9 +171,11 @@ code argQ argD
// has two (ff, ffrstmux) users
if (nusers(dffD) > 2)
argD = SigSpec();
}
endcode
// (2) Match for a $mux cell implementing synchronous reset semantics ---
// exclusively drives the 'D' input of the $dff, with one of the $mux
// inputs being fully zero
match ffrstmux
if !argD.empty()
select ffrstmux->type.in($mux)
@ -158,6 +207,10 @@ code argD
dffrstmux = nullptr;
endcode
// (3) Match for a $mux cell implement clock enable semantics --- one that
// exclusively drives the 'D' input of the $dff (or the other input of
// the reset $mux) and where one of this $mux's inputs is connected to
// the 'Q' output of the $dff
match ffcemux
if !argD.empty()
select ffcemux->type.in($mux)

113
passes/pmgen/xilinx_dsp_cascade.pmg
View file

@ -1,3 +1,46 @@
// This file describes the third of three pattern matcher setups that
// forms the `xilinx_dsp` pass described in xilinx_dsp.cc
// At a high level, it works as follows:
// (1) Starting from a DSP48E1 cell that (a) has the Z multiplexer
// (controlled by OPMODE[6:4]) set to zero and (b) doesn't already
// use the 'PCOUT' port
// (2.1) Match another DSP48E1 cell that (a) does not have the CREG enabled,
// (b) has its Z multiplexer output set to the 'C' port, which is
// driven by the 'P' output of the previous DSP cell, and (c) has its
// 'PCIN' port unused
// (2.2) Same as (2.1) but with the 'C' port driven by the 'P' output of the
// previous DSP cell right-shifted by 17 bits
// (3) For this subequent DSP48E1 match (i.e. PCOUT -> PCIN cascade exists)
// if (a) the previous DSP48E1 uses either the A2REG or A1REG, (b) this
// DSP48 does not use A2REG nor A1REG, (c) this DSP48E1 does not already
// have an ACOUT -> ACIN cascade, (d) the previous DSP does not already
// use its ACOUT port, then examine if an ACOUT -> ACIN cascade
// opportunity exists by matching for a $dff-with-optional-clock-enable-
// or-reset and checking that the 'D' input of this register is the same
// as the 'A' input of the previous DSP
// (4) Same as (3) but for BCOUT -> BCIN cascade
// (5) Recursively go to (2.1) until no more matches possible, keeping track
// of the longest possible chain found
// (6) The longest chain is then divided into chunks of no more than
// MAX_DSP_CASCADE in length (to prevent long cascades that exceed the
// height of a DSP column) with each DSP in each chunk being rewritten
// to use [ABP]COUT -> [ABP]CIN cascading as appropriate
// Notes:
// - Currently, [AB]COUT -> [AB]COUT cascades (3 or 4) are only considered
// if a PCOUT -> PCIN cascade is (2.1 or 2.2) first identified; this need
// not be the case --- [AB] cascades can exist independently of a P cascade
// (though all three cascades must come from the same DSP). This situation
// is not handled currently.
// - In addition, [AB]COUT -> [AB]COUT cascades (3 or 4) are currently
// conservative in that they examine the situation where (a) the previous
// DSP has [AB]2REG or [AB]1REG enabled, (b) that the downstream DSP has no
// registers enabled, and (c) that there exists only one additional register
// between the upstream and downstream DSPs. This can certainly be relaxed
// to identify situations ranging from (i) neither DSP uses any registers,
// to (ii) upstream DSP has 2 registers, downstream DSP has 2 registers, and
// there exists a further 2 registers between them. This remains a TODO
// item.
pattern xilinx_dsp_cascade
udata <std::function<SigSpec(const SigSpec&)>> unextend
@ -6,7 +49,7 @@ state <Cell*> next
state <SigSpec> clock
state <int> AREG BREG
// subpattern
// Variables used for subpatterns
state <SigSpec> argQ argD
state <bool> ffcepol ffrstpol
state <int> ffoffset
@ -19,12 +62,19 @@ code
#define MAX_DSP_CASCADE 20
endcode
// (1) Starting from a DSP48E1 cell that (a) has the Z multiplexer
// (controlled by OPMODE[6:4]) set to zero and (b) doesn't already
// use the 'PCOUT' port
match first
select first->type.in(\DSP48E1)
select port(first, \OPMODE, Const(0, 7)).extract(4,3) == Const::from_string("000")
select nusers(port(first, \PCOUT, SigSpec())) <= 1
endmatch
// (6) The longest chain is then divided into chunks of no more than
// MAX_DSP_CASCADE in length (to prevent long cascades that exceed the
// height of a DSP column) with each DSP in each chunk being rewritten
// to use [ABP]COUT -> [ABP]CIN cascading as appropriate
code
longest_chain.clear();
chain.emplace_back(first, -1, -1, -1);
@ -106,6 +156,10 @@ subpattern tail
arg first
arg next
// (2.1) Match another DSP48E1 cell that (a) does not have the CREG enabled,
// (b) has its Z multiplexer output set to the 'C' port, which is
// driven by the 'P' output of the previous DSP cell, and (c) has its
// 'PCIN' port unused
match nextP
select nextP->type.in(\DSP48E1)
select !param(nextP, \CREG, State::S1).as_bool()
@ -116,6 +170,8 @@ match nextP
semioptional
endmatch
// (2.2) Same as (2.1) but with the 'C' port driven by the 'P' output of the
// previous DSP cell right-shifted by 17 bits
match nextP_shift17
if !nextP
select nextP_shift17->type.in(\DSP48E1)
@ -145,6 +201,14 @@ code next
}
endcode
// (3) For this subequent DSP48E1 match (i.e. PCOUT -> PCIN cascade exists)
// if (a) the previous DSP48E1 uses either the A2REG or A1REG, (b) this
// DSP48 does not use A2REG nor A1REG, (c) this DSP48E1 does not already
// have an ACOUT -> ACIN cascade, (d) the previous DSP does not already
// use its ACOUT port, then examine if an ACOUT -> ACIN cascade
// opportunity exists by matching for a $dff-with-optional-clock-enable-
// or-reset and checking that the 'D' input of this register is the same
// as the 'A' input of the previous DSP
code argQ clock AREG
AREG = -1;
if (next) {
@ -152,7 +216,6 @@ code argQ clock AREG
if (param(prev, \AREG, 2).as_int() > 0 &&
param(next, \AREG, 2).as_int() > 0 &&
param(next, \A_INPUT, Const("DIRECT")).decode_string() == "DIRECT" &&
port(next, \ACIN, SigSpec()).is_fully_zero() &&
nusers(port(prev, \ACOUT, SigSpec())) <= 1) {
argQ = unextend(port(next, \A));
clock = port(prev, \CLK);
@ -174,6 +237,7 @@ reject_AREG: ;
}
endcode
// (4) Same as (3) but for BCOUT -> BCIN cascade
code argQ clock BREG
BREG = -1;
if (next) {
@ -203,13 +267,14 @@ reject_BREG: ;
}
endcode
// (5) Recursively go to (2.1) until no more matches possible, recording the
// longest possible chain
code
if (next) {
chain.emplace_back(next, nextP_shift17 ? 17 : nextP ? 0 : -1, AREG, BREG);
SigSpec sigC = unextend(port(next, \C));
// TODO: Cannot use 'reject' since semioptional
if (nextP_shift17) {
if (GetSize(sigC)+17 <= GetSize(port(std::get<0>(chain.back()), \P)) &&
port(std::get<0>(chain.back()), \P).extract(17, GetSize(sigC)) != sigC)
@ -232,22 +297,44 @@ endcode
// #######################
// Subpattern for matching against input registers, based on knowledge of the
// 'Q' input. Typically, identifying registers with clock-enable and reset
// capability would be a task would be handled by other Yosys passes such as
// dff2dffe, but since DSP inference happens much before this, these patterns
// have to be manually identified.
// At a high level:
// (1) Starting from a $dff cell that (partially or fully) drives the given
// 'Q' argument
// (2) Match for a $mux cell implementing synchronous reset semantics ---
// one that exclusively drives the 'D' input of the $dff, with one of its
// $mux inputs being fully zero
// (3) Match for a $mux cell implement clock enable semantics --- one that
// exclusively drives the 'D' input of the $dff (or the other input of
// the reset $mux) and where one of this $mux's inputs is connected to
// the 'Q' output of the $dff
subpattern in_dffe
arg argD argQ clock
code
dff = nullptr;
for (auto c : argQ.chunks()) {
for (const auto &c : argQ.chunks()) {
// Abandon matches when 'Q' is a constant
if (!c.wire)
reject;
// Abandon matches when 'Q' has the keep attribute set
if (c.wire->get_bool_attribute(\keep))
reject;
Const init = c.wire->attributes.at(\init, State::Sx);
if (!init.is_fully_undef() && !init.is_fully_zero())
// Abandon matches when 'Q' has a non-zero init attribute set
// (not supported by DSP48E1)
Const init = c.wire->attributes.at(\init, Const());
for (auto b : init.extract(c.offset, c.width))
if (b != State::Sx && b != State::S0)
reject;
}
endcode
// (1) Starting from a $dff cell that (partially or fully) drives the given
// 'Q' argument
match ff
select ff->type.in($dff)
// DSP48E1 does not support clock inversion
@ -260,14 +347,12 @@ match ff
filter GetSize(port(ff, \Q)) >= offset + GetSize(argQ)
filter port(ff, \Q).extract(offset, GetSize(argQ)) == argQ
filter clock == SigBit() || port(ff, \CLK) == clock
set ffoffset offset
endmatch
code argQ argD
{
if (clock != SigBit() && port(ff, \CLK) != clock)
reject;
SigSpec Q = port(ff, \Q);
dff = ff;
dffclock = port(ff, \CLK);
@ -279,9 +364,11 @@ code argQ argD
// has two (ff, ffrstmux) users
if (nusers(dffD) > 2)
argD = SigSpec();
}
endcode
// (2) Match for a $mux cell implementing synchronous reset semantics ---
// exclusively drives the 'D' input of the $dff, with one of the $mux
// inputs being fully zero
match ffrstmux
if !argD.empty()
select ffrstmux->type.in($mux)
@ -313,6 +400,10 @@ code argD
dffrstmux = nullptr;
endcode
// (3) Match for a $mux cell implement clock enable semantics --- one that
// exclusively drives the 'D' input of the $dff (or the other input of
// the reset $mux) and where one of this $mux's inputs is connected to
// the 'Q' output of the $dff
match ffcemux
if !argD.empty()
select ffcemux->type.in($mux)

6
techlibs/xilinx/synth_xilinx.cc
View file

@ -342,7 +342,11 @@ struct SynthXilinxPass : public ScriptPass
if (check_label("map_dsp", "(skip if '-nodsp')")) {
if (!nodsp || help_mode) {
// NB: Xilinx multipliers are signed only
run("techmap -map +/mul2dsp.v -map +/xilinx/dsp_map.v -D DSP_A_MAXWIDTH=25 -D DSP_A_MAXWIDTH_PARTIAL=18 -D DSP_B_MAXWIDTH=18 "
run("techmap -map +/mul2dsp.v -map +/xilinx/dsp_map.v -D DSP_A_MAXWIDTH=25 "
"-D DSP_A_MAXWIDTH_PARTIAL=18 -D DSP_B_MAXWIDTH=18 " // Partial multipliers are intentionally
// limited to 18x18 in order to take
// advantage of the (PCOUT << 17) -> PCIN
// dedicated cascade chain capability
"-D DSP_A_MINWIDTH=2 -D DSP_B_MINWIDTH=2 " // Blocks Nx1 multipliers
"-D DSP_Y_MINWIDTH=9 " // UG901 suggests small multiplies are those 4x4 and smaller
"-D DSP_SIGNEDONLY=1 -D DSP_NAME=$__MUL25X18");