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xilinx: Treat DSP48E1 as 24x17 unsigned for now (actual behaviour is 25x18 signed)

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Signed-off-by: David Shah <dave@ds0.me>
This commit is contained in:
David Shah 2019-07-16 16:46:41 +01:00
parent 8da4c1ad82
commit 95c8d27b0b
2 changed files with 8 additions and 4 deletions
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6
techlibs/xilinx/synth_xilinx.cc
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@ -284,8 +284,12 @@ struct SynthXilinxPass : public ScriptPass
run("techmap -map +/cmp2lut.v -D LUT_WIDTH=6");
// The actual behaviour of the Xilinx DSP is a signed 25x18 multiply
// Due to current limitations of mul2dsp, we are actually mapping as a 24x17
// unsigned multiply with MSBs set to 1'b0
if (!nodsp || help_mode)
run("techmap -map +/mul2dsp.v -D DSP_A_MAXWIDTH=25 -D DSP_B_MAXWIDTH=18 -D DSP_NAME=$__MUL25X18");
run("techmap -map +/mul2dsp.v -D DSP_A_MAXWIDTH=24 -D DSP_B_MAXWIDTH=17 -D DSP_NAME=$__MUL25X18");
run("alumacc");
run("share");