Altera Nios II C2H Compiler Manuel d'utilisateur télécharger pdf (Page 44)

3–4 9.1 Altera Corporation

Nios II C2H Compiler User Guide November 2009

One-to-One C-to-Hardware Mapping

Pipelined Operations and Assignments

The C2H Compiler always registers the results of the operators listed in

Table 3–3. Some arithmetic operations, such as multiplication, use a large

amount of logic, which creates a significant propagation delay through

the circuit. Calculating these operations in series with other operations in

a single clock cycle would incur unacceptable propagation delays and

significantly reduce the maximum achievable clock frequency (f

MAX

) for

the system. The C2H Compiler pipelines these operations by giving each

its own registered assignment. There are exceptions for cases in which an

operation reduces to trivial logic, as listed in Table 3–3

The general rule "one registered assignment for every = operator" can be

amended to read, "one registered assignment for every = operator or

complex arithmetic operator".

Table 3–3. Complex Arithmetic Operations Pipelined by the C2H Compiler

Operator Description Exceptions

Multiplication Either operand is a constant power of

2, which reduces to left-shift operation

Division Right-hand operand is a constant

power of 2, which reduces to a right-

shift operation

Modulus Right-hand operand is a constant

power of 2, which reduces to a

masking operation

Right bit-wise shift Right-hand side is constant

Left bit-wise shift Right-hand side is constant

1 2 ... 39 40 41 42 43 44 45 46 47 48 49 ... 137 138

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Altera Nios II C2H Compiler Manuel d'utilisateur Page 44