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| author | Eddie Hung <eddie@fpgeh.com> | 2019-10-04 22:30:14 -0700 |
|---|---|---|
| committer | Eddie Hung <eddie@fpgeh.com> | 2019-10-04 22:31:04 -0700 |
| commit | 6c5e1234e19159b7577a5e64a7a463142160f7ff (patch) | |
| tree | 8980ae678afd809e06004e157d8e6220e52d05d9 /techlibs | |
| parent | 792cd31052d32d661a995df0c46f5cb9f27b566b (diff) | |
| download | yosys-6c5e1234e19159b7577a5e64a7a463142160f7ff.tar.gz yosys-6c5e1234e19159b7577a5e64a7a463142160f7ff.tar.bz2 yosys-6c5e1234e19159b7577a5e64a7a463142160f7ff.zip | |
Add comment on why partial multipliers are 18x18
Diffstat (limited to 'techlibs')
| -rw-r--r-- | techlibs/xilinx/synth_xilinx.cc | 12 |
1 files 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"); |