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Reduced number of cycles required for lower-precision sqrt

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This commit is contained in:
David Harris 2022-09-17 09:55:34 -07:00
parent ac78823f6c
commit b74a68ff0f
2 changed files with 44 additions and 3 deletions
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4
pipelined/src/fpu/fdivsqrt.sv
View File

@ -67,8 +67,8 @@ module fdivsqrt(
.clk, .DivStart(DivStartE), .Xm(XmE), .QeM, .Xe(XeE), .Fmt(FmtE), .Ye(YeE),
.Sqrt(SqrtE), .Ym(YmE), .XZero(XZeroE), .X, .Dpreproc);
fdivsqrtfsm fdivsqrtfsm(
.reset, .XsE, .SqrtE,
.DivBusy, .clk, .DivStart(DivStartE),.StallE, .StallM, .DivDone, .XZeroE, .YZeroE,
.clk, .reset, .FmtE, .XsE, .SqrtE,
.DivBusy, .DivStart(DivStartE),.StallE, .StallM, .DivDone, .XZeroE, .YZeroE,
.XNaNE, .YNaNE,
.XInfE, .YInfE, .EarlyTermShiftE(EarlyTermShiftM), .WZero);
fdivsqrtiter fdivsqrtiter(

43
pipelined/src/fpu/fdivsqrtfsm.sv
View File

@ -33,6 +33,7 @@
module fdivsqrtfsm(
input logic clk,
input logic reset,
input logic [`FMTBITS-1:0] FmtE,
input logic XInfE, YInfE,
input logic XZeroE, YZeroE,
input logic XNaNE, YNaNE,
@ -59,13 +60,53 @@ module fdivsqrtfsm(
// terminate immediately on special cases
assign SpecialCase = XZeroE | (YZeroE&~SqrtE) | XInfE | YInfE | XNaNE | YNaNE | (XsE&SqrtE);
assign cycles = (`DURLEN)'((`DIVN+2+(`LOGR*`DIVCOPIES)-1)/(`LOGR*`DIVCOPIES)+(`RADIX/4));
// DIVN = `NF+3
// NS = NF + 1
// N = NS or NS+2 for div/sqrt.
/* verilator lint_off WIDTH */
logic [`DURLEN+1:0] Nf, fbits; // number of fractional bits
if (`FPSIZES == 1)
assign Nf = `NF;
else if (`FPSIZES == 2)
always_comb
case (FmtE)
1'b0: Nf = `NF1;
1'b1: Nf = `NF;
endcase
else if (`FPSIZES == 3)
always_comb
case (FmtE)
`FMT: Nf = `NF;
`FMT1: Nf = `NF1;
`FMT2: Nf = `NF2;
endcase
else if (`FPSIZES == 4)
always_comb
case(FmtE)
`S_FMT: Nf = `S_NF;
`D_FMT: Nf = `D_NF;
`H_FMT: Nf = `H_NF;
`Q_FMT: Nf = `Q_NF;
endcase
always_comb begin
if (SqrtE) fbits = Nf + 2 + 2; // Nf + two fractional bits for round/guard + 2 for right shift by up to 2
else fbits = Nf + 2 + `LOGR; // Nf + two fractional bits for round/guard + integer bits - try this when placing results in msbs
if (SqrtE) cycles = (fbits + (`LOGR*`DIVCOPIES)-1)/(`LOGR*`DIVCOPIES); // ceiling(fbits / r*k)
else cycles = `FPDUR; // *** line above should work once otfc is used to put results in upper bits
end
/* verilator lint_on WIDTH */
always_ff @(posedge clk) begin
if (reset) begin
state <= #1 IDLE;
end else if (DivStart&~StallE) begin
step <= cycles; // *** this should be adjusted to depend on the precision; sqrt should use one fewer step becasue firststep=1
// $display("Setting Nf = %d fbits %d cycles = %d FmtE %d FPSIZES = %d Q_NF = %d num = %d denom = %d\n", Nf, fbits, cycles, FmtE, `FPSIZES, `Q_NF,
// (fbits +(`LOGR*`DIVCOPIES)-1), (`LOGR*`DIVCOPIES));
if (SpecialCase) state <= #1 DONE;
else state <= #1 BUSY;
end else if (DivDone) begin