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🐛 Fix fdiv/fsqrt directed rounding in the legacy divsqrt unit #28

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🐛 Fix fdiv/fsqrt directed rounding in the legacy divsqrt unit #28

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18 changes: 17 additions & 1 deletion src/fpnew_divsqrt_multi.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -278,14 +278,30 @@ module fpnew_divsqrt_multi #(
fpnew_pkg::status_t unit_status, held_status_q;
logic hold_en;

// Translate the fpnew RISC-V roundmode encoding into the legacy PULP
// div_sqrt_top_mvp RM_SI encoding. Nearest-even and truncate agree, but
// round-down and round-up are swapped, and the legacy unit has no
// ties-to-max mode, so map it to nearest-even.
logic [2:0] divsqrt_rm;
always_comb begin
unique case (rnd_mode_q)
fpnew_pkg::RNE: divsqrt_rm = 3'h0;
fpnew_pkg::RTZ: divsqrt_rm = 3'h1;
fpnew_pkg::RDN: divsqrt_rm = 3'h3;
fpnew_pkg::RUP: divsqrt_rm = 3'h2;
fpnew_pkg::RMM: divsqrt_rm = 3'h0;
default: divsqrt_rm = 3'h0;
endcase
end

div_sqrt_top_mvp i_divsqrt_lei (
.Clk_CI ( clk_i ),
.Rst_RBI ( rst_ni ),
.Div_start_SI ( div_valid ),
.Sqrt_start_SI ( sqrt_valid ),
.Operand_a_DI ( divsqrt_operands[0] ),
.Operand_b_DI ( divsqrt_operands[1] ),
.RM_SI ( rnd_mode_q ),
.RM_SI ( divsqrt_rm ),
.Precision_ctl_SI ( '0 ),
.Format_sel_SI ( divsqrt_fmt ),
.Kill_SI ( flush_i ),
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