Altera Nios II C2H Compiler Manuel d'utilisateur télécharger pdf (Page 80)

3–40 9.1 Altera Corporation

Nios II C2H Compiler User Guide November 2009

Scheduling

For the purposes of scheduling, the C2H Compiler treats a loop and its

dependencies as a unit. No lines of code past the loop block execute until

the whole loop completes. Figure 3–19 shows the dependency graph for

the function transform_and_hash_matrix(), shown in

Example 3–33.

Example 3–33. Dependency Graph for a Function Containing a Loop

int transform_and_hash_matrix(int *matrix,

int length, int width)

{

int n_words = length * width;

int hash = 1;

int i;

for (i=0; i<n_words; i++)

{

...perform some transform...

hash = ...some hash calculation...

}

return hash;

}

Figure 3–19. Dependency Graph for a Function Containing a Loop

As shown in Figure 3–19, some part of the for loop depends on

n_words, and so the C2H Compiler does not schedule the loop until after

the assignment to n_words completes. The return statement outside

the loop depends on hash, which is assigned inside the loop. As a result,

the C2H Compiler does not schedule the return statement until the loop

completes.

In this case, the state machine for transform_and_hash_matrix()

has three states. However, the state machine does not complete in three

clock cycles, because State 1 consists of a sub-state-machine, which

requires multiple clock cycles to complete.

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Altera Nios II C2H Compiler Manuel d'utilisateur Page 80