diff options
Diffstat (limited to 'passes/pmgen/xilinx_dsp.pmg')
| -rw-r--r-- | passes/pmgen/xilinx_dsp.pmg | 214 |
1 files changed, 175 insertions, 39 deletions
diff --git a/passes/pmgen/xilinx_dsp.pmg b/passes/pmgen/xilinx_dsp.pmg index 4e174e753..604aa222b 100644 --- a/passes/pmgen/xilinx_dsp.pmg +++ b/passes/pmgen/xilinx_dsp.pmg @@ -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()) - reject; + // 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 @@ -558,32 +696,30 @@ 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) { - argQ = argD; - argQ.replace(D, Q); - } - - for (auto c : argQ.chunks()) { - Const init = c.wire->attributes.at(\init, State::Sx); - if (!init.is_fully_undef() && !init.is_fully_zero()) - reject; - } + SigSpec D = port(ff, \D); + SigSpec Q = port(ff, \Q); + if (!ffcemux) { + argQ = argD; + argQ.replace(D, Q); + } - dff = ff; - dffQ = argQ; - dffclock = port(ff, \CLK); + // 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, Const()); + if (!init.empty()) + for (auto b : init.extract(c.offset, c.width)) + if (b != State::Sx && b != State::S0) + reject; } - // No enable/reset mux possible without flop - else if (dffcemux || dffrstmux) - reject; + + dff = ff; + dffQ = argQ; + dffclock = port(ff, \CLK); endcode |