From 6c5e1234e19159b7577a5e64a7a463142160f7ff Mon Sep 17 00:00:00 2001 From: Eddie Hung Date: Fri, 4 Oct 2019 22:30:14 -0700 Subject: [PATCH] Add comment on why partial multipliers are 18x18 --- techlibs/xilinx/synth_xilinx.cc | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/techlibs/xilinx/synth_xilinx.cc b/techlibs/xilinx/synth_xilinx.cc index 41429b338..4fe287744 100644 --- a/techlibs/xilinx/synth_xilinx.cc +++ b/techlibs/xilinx/synth_xilinx.cc @@ -342,10 +342,14 @@ 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 " - "-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=$__MUL25X18"); + run("techmap -map +/mul2dsp.v -map +/xilinx/dsp_map.v -D DSP_A_MAXWIDTH=25 " + "-D DSP_A_MAXWIDTH_PARTIAL=18 -D DSP_B_MAXWIDTH=18 " // Partial multipliers are intentionally + // limited to 18x18 in order to take + // advantage of the (PCOUT << 17) -> PCIN + // dedicated cascade chain capability + "-D DSP_A_MINWIDTH=2 -D DSP_B_MINWIDTH=2 " // Blocks Nx1 multipliers + "-D DSP_Y_MINWIDTH=9 " // UG901 suggests small multiplies are those 4x4 and smaller + "-D DSP_SIGNEDONLY=1 -D DSP_NAME=$__MUL25X18"); run("select a:mul2dsp"); run("setattr -unset mul2dsp"); run("opt_expr -fine"); -- 2.30.2