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Commentary (#2290).

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Wilson Snyder 2020-04-28 18:46:59 -04:00
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@ -5271,17 +5271,21 @@ be accessing with a /*verilator public*/ comment before the closing
semicolon. Then scope into the C++ class to read the value of the signal, semicolon. Then scope into the C++ class to read the value of the signal,
as you would any other member variable. as you would any other member variable.
Signals are the smallest of 8-bit chars, 16-bit shorts, 32-bit longs, or Signals are the smallest of 8-bit unsigned chars (equivalent to uint8_t),
64-bit long longs that fits the width of the signal. Generally, you can 16-bit unsigned shorts (uint16_t), 32-bit unsigned longs (uint32_t), or
use just uint32_t's for 1 to 32 bits, or vluint64_t for 1 to 64 bits, and 64-bit unsigned long longs (uint64_t) that fits the width of the signal.
the compiler will properly up-convert smaller entities. Generally, you can use just uint32_t's for 1 to 32 bits, or vluint64_t for
1 to 64 bits, and the compiler will properly up-convert smaller entities.
Note even signed ports are declared as unsigned; you must sign extend
yourself to the appropriate signal width.
Signals wider than 64 bits are stored as an array of 32-bit uint32_t's. Signals wider than 64 bits are stored as an array of 32-bit uint32_t's.
Thus to read bits 31:0, access signal[0], and for bits 63:32, access Thus to read bits 31:0, access signal[0], and for bits 63:32, access
signal[1]. Unused bits (for example bit numbers 65-96 of a 65-bit vector) signal[1]. Unused bits (for example bit numbers 65-96 of a 65-bit vector)
will always be zero. if you change the value you must make sure to pack will always be zero. If you change the value you must make sure to pack
zeros in the unused bits or core-dumps may result. (Because Verilator zeros in the unused bits or core-dumps may result, because Verilator strips
strips array bound checks where it believes them to be unnecessary.) array bound checks where it believes them to be unnecessary to improve
performance.
In the SYSTEMC example above, if you had in our.v: In the SYSTEMC example above, if you had in our.v: