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[rtl] Make sure decoder also checks bits 26 and 25 for slli, srli, srai

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Previously, these bits were not checked when decoding slli, srli and
srai, causing some illegal instruction encodings not to trigger an
illegal instructions exception.

This resolves lowRISC/Ibex#1018.

Signed-off-by: Pirmin Vogel <vogelpi@lowrisc.org>
This commit is contained in:
Pirmin Vogel 2020-07-16 16:15:51 +02:00
parent 03a8ae70d6
commit 7f9e704f36
1 changed files with 2 additions and 2 deletions
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4
rtl/ibex_decoder.sv
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@ -348,7 +348,7 @@ module ibex_decoder #(
3'b001: begin 3'b001: begin
unique case (instr[31:27]) unique case (instr[31:27])
5'b0_0000: illegal_insn = 1'b0; // slli 5'b0_0000: illegal_insn = (instr[26:25] == 2'b00) ? 1'b0 : 1'b1; // slli
5'b0_0100, // sloi 5'b0_0100, // sloi
5'b0_1001, // sbclri 5'b0_1001, // sbclri
5'b0_0101, // sbseti 5'b0_0101, // sbseti
@ -385,7 +385,7 @@ module ibex_decoder #(
end else begin end else begin
unique case (instr[31:27]) unique case (instr[31:27])
5'b0_0000, // srli 5'b0_0000, // srli
5'b0_1000: illegal_insn = 1'b0; // srai 5'b0_1000: illegal_insn = (instr[26:25] == 2'b00) ? 1'b0 : 1'b1; // srai
5'b0_0100, // sroi 5'b0_0100, // sroi
5'b0_1100, // rori 5'b0_1100, // rori