Determining The Minimum Iteration Interval; Resource Table For Iir Filter - Texas Instruments TMS320C6000 Programmer's Manual

Loop Carry Paths
6.7.4

Determining the Minimum Iteration Interval

Table 6–16. Resource Table for IIR Filter
(a) A side
Unit(s) Instructions
.M1 2 MPYs
.S1 B
.D1 2 LDHs
.L1,.S1, or .D1 ADD & SUB
Total non-.M units
6-80
To determine the minimum iteration interval, you must consider both resources
and data dependency constraints. Based on resources in Table 6–16, the
minimum iteration interval is 2.
Note:
There are six non-.M units available: three on the A side (.S1, .D1, .L1) and
three on the B side (.S2, .D2, .L2). Therefore, to determine resource
constraints, divide the total number of non-.M units used on each side by 3
(3 is the total number of non-.M units available on each side).
Based on non-.M unit resources in Table 6–16, the minimum iteration inter-
val for the IIR filter is 2 because the total non-.M units on the A side is 5 (5
is greater than 1 so you round up to the next whole number). The B side uses
only three non-.M units, so this does not affect the minimum iteration interval,
and no other unit is used more than twice.
Total/Unit
2
1
2
2
5
However, the IIR has a data dependency constraint defined by its loop carry
path. Figure 6–15 shows that if you schedule LDH yi on cycle 0:
The earliest you can schedule MPY p2 is on cycle 5.
The earliest you can schedule ADD s1 is on cycle 7.
SHR yi+1 must be on cycle 8 and STH on cycle 9.
Because the LDH must wait for the STH to be issued, the earliest the the
second iteration can begin is cycle 10.
To determine the minimum loop carry path, add all of the numbers along the
loop paths in the dependency graph. This means that this loop carry path is
10 (5 + 2 + 1 + 1 + 1).
(b) B side
Unit(s) Instructions
.M2 MPY
.S2 SHR
.D2 STH
.L2 or .S2, .D2 ADD
Total non-.M units
3
Total/Unit
1
1
1
1
3