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authorClifford Wolf <clifford@clifford.at>2014-09-02 23:21:59 +0200
committerClifford Wolf <clifford@clifford.at>2014-09-02 23:21:59 +0200
commit635b922afeabea8c69ac4e749881b10aeda7448b (patch)
treebce3fc8ace4bd5f0bc40c429ec38b8bd1e097af6 /techlibs
parentf1869667cac35e897c0531c05074f3c77bfa5db9 (diff)
Undef-related fixes in simlib $alu model
Diffstat (limited to 'techlibs')
-rw-r--r--techlibs/common/simlib.v9
1 files changed, 6 insertions, 3 deletions
diff --git a/techlibs/common/simlib.v b/techlibs/common/simlib.v
index 09ffa9a6..61215f59 100644
--- a/techlibs/common/simlib.v
+++ b/techlibs/common/simlib.v
@@ -492,8 +492,11 @@ generate
end
endgenerate
+// this is 'x' if Y and CO should be all 'x', and '0' otherwise
+wire y_co_undef = ^{A, A, B, B, CI, CI, BI, BI};
+
assign X = AA ^ BB;
-assign Y = AA + BB + CI;
+assign Y = (AA + BB + CI) ^ {Y_WIDTH{y_co_undef}};
function get_carry;
input a, b, c;
@@ -502,9 +505,9 @@ endfunction
genvar i;
generate
- assign CO[0] = get_carry(AA[0], BB[0], CI);
+ assign CO[0] = get_carry(AA[0], BB[0], CI) ^ y_co_undef;
for (i = 1; i < Y_WIDTH; i = i+1) begin:BLOCK3
- assign CO[i] = get_carry(AA[i], BB[i], CO[i-1]);
+ assign CO[i] = get_carry(AA[i], BB[i], CO[i-1]) ^ y_co_undef;
end
endgenerate