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Issue #894: trap on floating-point ops with reserved rounding modes

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David Harris 2024-07-25 06:59:58 -07:00
parent b7fb786749
commit 337e40ac1b
1 changed files with 5 additions and 2 deletions
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7
src/fpu/fctrl.sv
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@ -81,6 +81,7 @@ module fctrl import cvw::*; #(parameter cvw_t P) (
logic [1:0] Fmt, Fmt2; // format - before possible reduction
logic SupportedFmt; // is the format supported
logic SupportedFmt2; // is the source format supported for fp -> fp
logic SupportedRM; // is the rounding mode supported
logic FCvtIntD, FCvtIntM; // convert to integer operation
logic ZfaD; // Zfa variants of instructions
logic ZfaFRoundNXD; // Zfa froundnx instruction
@ -93,14 +94,16 @@ module fctrl import cvw::*; #(parameter cvw_t P) (
(Fmt == 2'b10 & P.ZFH_SUPPORTED) | (Fmt == 2'b11 & P.Q_SUPPORTED));
assign SupportedFmt2 = (Fmt2 == 2'b00 | (Fmt2 == 2'b01 & P.D_SUPPORTED) |
(Fmt2 == 2'b10 & P.ZFH_SUPPORTED) | (Fmt2 == 2'b11 & P.Q_SUPPORTED));
// rounding modes 5 and 6 are reserved. Rounding mode 7 is dynamic, and is reserved if FRM is 5, 6, or 7
assign SupportedRM = ~(Funct3D == 3'b101 | Funct3D == 3'b110 | (Funct3D == 3'b111 & (FRM_REGW == 3'b101 | FRM_REGW == 3'b110 | FRM_REGW == 3'b111)));
// decode the instruction
// FRegWrite_FWriteInt_FResSel_PostProcSel_FOpCtrl_FDivStart_IllegalFPUInstr_FCvtInt_Zfa_FroundNX
always_comb
if (STATUS_FS == 2'b00) // FPU instructions are illegal when FPU is disabled
ControlsD = `FCTRLW'b0_0_00_00_000_0_1_0_0_0;
else if (OpD != 7'b0000111 & OpD != 7'b0100111 & ~SupportedFmt)
ControlsD = `FCTRLW'b0_0_00_00_000_0_1_0_0_0; // for anything other than loads and stores, check for supported format
else if (OpD != 7'b0000111 & OpD != 7'b0100111 & (~SupportedFmt | ~SupportedRM))
ControlsD = `FCTRLW'b0_0_00_00_000_0_1_0_0_0; // for anything other than loads and stores, check for supported format and rounding mode
else begin
ControlsD = `FCTRLW'b0_0_00_00_000_0_1_0_0_0; // default: non-implemented instruction
/* verilator lint_off CASEINCOMPLETE */ // default value above has priority so no other default needed