Computer Hardware User's Guide

Circular Addressing
6-24
Example 6–24. Circular Addressing
*AR0++(5)% ; AR0 = 0 (0 value)
*AR0++(2)% ; AR0 = 5 (1st value)
*AR0– –(3)% ; AR0 = 1 (2nd value)
*AR0++(6)% ; AR0 = 4 (3rd value)
*AR0– –% ; AR0 = 4 (4th value)
*AR0 ; AR0 = 3 (5th value)
Element 0
Element 1
Element 2
Element 3
Element 4
Element 5 (last element)
Last element + 1
0
1
2
3
4
5
6
0
2nd
5th
4th, 3rd
1st
Value Data Address
→
→
→
→
→
Circular addressing is especially useful for the implementation of FIR filters.
Figure 6–8 shows one possible data structure for FIR filters. Note that the ini-
tial value of AR0 points to h(N–1), and the initial value of AR1 points to x(0).
Circular addressing is used in the ’C3x code for the FIR filter shown in
Example 6–25.
Figure 6–8. Data Structure for FIR Filters
h(N–1)
h(N–2)
h(2)
h(1)
h(0)
x(N–1)
x(N–2)
x(2)
x(1)
x(0)
AR0
AR1
Impulse response Input samples
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