Altera Nios II C2H Compiler - Manual (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.