Dependency Graph Of Iir Filter (With Smaller Loop Carry) - Texas Instruments TMS320C6000 Programmer's Manual

6.7.4.1 Drawing a New Dependency Graph
Figure 6–16. Dependency Graph of IIR Filter (With Smaller Loop Carry)
Although the minimum iteration interval is the greater of the resource limits and
data dependency constraints, an interval of 10 seems slow. Figure 6–16
shows how to improve the performance.
Figure 6–16 shows a new graph with a loop carry path of 4 (2 +1 + 1). because
the MPY p2 instruction can read yi+1 while it is still in a register, you can reduce
the loop carry path by six cycles. LDH yi is no longer in the graph. Instead, you
can issue LDH y[0] once outside the loop. In every iteration after that, the y+1
values written by the SHR instruction are valid y inputs to the MPY instruction.
LDH
xi
5
p0
2
SUB
cntr
1
1
Loop
Note: The shaded numbers show the loop carry path: 2 + 1 + 1 = 4.
Optimizing Assembly Code via Linear Assembly
A side
LDH
xi+1
5
MPY MPY
p1
ADD
2
s0
ADD
1
s1
1
SHR
yi+1
1
B STH
mem
Loop Carry Paths
B side
MPY
p2
2
1
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