Altera Nios II C2H Compiler Uživatelský manuál stáhnout pdf (Strana 46)

3–6 9.1 Altera Corporation

Nios II C2H Compiler User Guide November 2009

One-to-One C-to-Hardware Mapping

The fundamental iteration statement for the C2H Compiler is the do loop,

which evaluates its condition at the end of each iteration. See section

“Loop Pipelining” on page 3–42 for information about loop state

machines and scheduling.

Selection Statements

A selection statement (if-else, case, switch, and ?:) translates to a

multiplexer in hardware. The structure of the hardware depends on the

type of statement, as described in the following sections.

if Statement

An if-else statement translates to three elements in hardware:

■ Logic to perform all operations in the then block

■ Logic to perform all operations in the else block

■ Selection logic that determines which result to use

The results of each element are registered, and the registered signals feed

a multiplexer.

If the if statement has both a then and an else block, the operations for

both blocks execute in parallel. When all operations have completed, the

multiplexer selects which value propagates to subsequent statements,

based on the value of the control expression.

Figure 3–4 shows the circuit that results from the code in Example 3–2.

Example 3–2. If-else Logic

if (foo > bar)

foo += bar;

else

foo *= bar;

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Altera Nios II C2H Compiler Uživatelský manuál Strana 46