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No run time error for out of boundry access to array

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Hi, The following code: module x; bit[1:0] y[]; initial begin y = new[2]; y[0] = 2; y[1] = 3; for (int i=0; i


Originally posted in cdnusers.org by avidan_e
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  • In standard Verilog, out-of-bounds array access is permitted by the HDL language. The value returned is simply 'bx or the unknown value. This is the way that hardware would work, you can index with an invalid address and the hardware will return something, you just don't know what it will be.

    Since you are using an array of 'bit', you won't see an unknown value returned since 'bit' is only 2-state. So instead you see 'b0 as the return value.

    Here's what the SV LRM says in section 5.3.

    If an index expression is out of the address bounds or if any bit in the address is X or Z, then the index shall
    be invalid. The result of reading from an array with an invalid index shall return the default uninitialized
    value for the array element type.


    Originally posted in cdnusers.org by TAM
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  • In standard Verilog, out-of-bounds array access is permitted by the HDL language. The value returned is simply 'bx or the unknown value. This is the way that hardware would work, you can index with an invalid address and the hardware will return something, you just don't know what it will be.

    Since you are using an array of 'bit', you won't see an unknown value returned since 'bit' is only 2-state. So instead you see 'b0 as the return value.

    Here's what the SV LRM says in section 5.3.

    If an index expression is out of the address bounds or if any bit in the address is X or Z, then the index shall
    be invalid. The result of reading from an array with an invalid index shall return the default uninitialized
    value for the array element type.


    Originally posted in cdnusers.org by TAM
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