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Decoder: avoid setting PC upon illegal JALR instructions

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Without this commit, the PC is still set to a possible wrong jump
target on illegal JALR instructions ultimately causing the wrong PC
being saved to `mepc` during the illegal instruction exception.

This bug has been reported by @taoliug. This commit resolves #170.
This commit is contained in:
Pirmin Vogel 2019-07-18 11:18:40 +01:00
parent 63702b3e75
commit 04f4cd44f6
1 changed files with 3 additions and 2 deletions
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5
rtl/ibex_decoder.sv
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@ -602,9 +602,9 @@ module ibex_decoder #(
end
// make sure illegal instructions detected in the decoder do not propagate from decoder
// into register file, LSU, EX, WB, CSRs
// into register file, LSU, EX, WB, CSRs, PC
// NOTE: instructions can also be detected to be illegal inside the CSRs (upon accesses with
// insufficient privileges), in ID stage (when accessing Reg 16 or higher in RV32E config),
// insufficient privileges), or when accessing non-available registers in RV32E,
// these cases are not handled here
if (illegal_insn) begin
regfile_we = 1'b0;
@ -613,6 +613,7 @@ module ibex_decoder #(
mult_en_o = 1'b0;
div_en_o = 1'b0;
jump_in_dec_o = 1'b0;
jump_set_o = 1'b0;
branch_in_dec_o = 1'b0;
csr_access_o = 1'b0;
end