Altera Nios II C2H Compiler Manual de usuario descargar pdf (Pagina 107)

Altera Corporation 9.1 4–13

November 2009 Nios II C2H Compiler User Guide

Understanding the C2H View

Figure 4–5. CRC Dependency Graph

Since the critical path does not involve the pointer data the only

operations are on local scalar types and a read operation from the array

table. The calculation of lut_addr only depends on the scalar critical

loop variable crc, while the calculation of crc depends on a memory

reference to critical loop array variable table.

Each time the C2H accelerator finishes calculating the value of crc for

loop iteration n, it can start calculating crc for iteration n+1. On the same

clock cycle, it can also start calculating the value of lut_addr for

iteration n+2. This means that the accelerator always gets a one-loop head

start on calculating lut_addr. Thus, although the accelerator requires

lut_addr to calculate crc, lut_addr does not limit the loop speed,

because it is always ready as soon as crc is.

The report shows that the critical path is either 0--->6, or 6--->11.

Since the C2H Compiler pipelines the logic contained in loops, multiple

states are active concurrently. Figure 4–6 represents the pipelined timing

of Example 4–2 on page 4–10. Notice that since the assignment of crc is

the critical path, the accelerator begins each execution of that statement as

crc=(crc>>8)^table[lut_addr];

lut_addr=(

crc&0xFF)^*data++; lut_addr=(crc&0xFF)^*data++;

1 2 ... 102 103 104 105 106 107 108 109 110 111 112 ... 137 138

Sin comentarios

Altera Nios II C2H Compiler Manual de usuario Pagina 107