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Implement mstatush as hardwired-0, as required by priv-1.12

This commit is contained in:
Luke Wren 2021-07-23 21:52:01 +01:00
parent 2ae30183aa
commit 279e4b4f29
1 changed files with 8 additions and 3 deletions
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11
hdl/hazard3_csr.v
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@ -115,6 +115,7 @@ localparam MHARTID = 12'hf14; // Hardware thread ID.
// Machine Trap Setup (RW)
localparam MSTATUS = 12'h300; // Machine status register.
localparam MSTATUSH = 12'h310; // As of priv-1.12 this must be present even if tied 0.
localparam MISA = 12'h301; // ISA and extensions
localparam MEDELEG = 12'h302; // Machine exception delegation register.
localparam MIDELEG = 12'h303; // Machine interrupt delegation register.
@ -625,9 +626,13 @@ always @ (*) begin
};
end
// MSTATUSH is not implemented (permitted when all fields would be tied to
// zero -- those fields being MBE and SBE, which are zero because we are
// pure little-endian.)
// MSTATUSH is all zeroes (fields are MBE and SBE, which are zero because
// we are pure little-endian.) Prior to priv-1.12 MSTATUSH could be left
// unimplemented in this case, but now it must be decoded even if
// hardwired to 0.
MSTATUSH: if (CSR_M_MANDATORY || CSR_M_TRAP) begin
decode_match = 1'b1;
end
// MEDELEG, MIDELEG should not exist for M-only implementations. Will raise
// illegal instruction exception if accessed.