Circular Buffer With Amode - Texas Instruments TMS320C28x Reference Manual

Indirect Addressing Modes
Figure 5−1. Circular Buffer with AMODE = 0
Example(s):
; Calculate FIR filter (X[N] = data array, C[N] = coefficient array):
MOVW DP,#Xpointer
MOVL XAR6,@Xpointer
MOVL XAR7,#C
MOV @AR1,#N
SPM −4
ZAPA
RPT #N−1
||QMACL P,*AR6%++,*XAR7++
ADDL ACC,P << PM
MOVL @Xpointer,XAR6
MOVL @Sum,ACC
5-22
Top of buffer
Bottom of buffer
; Load DP with page address of Xpointer
; Load XAR6 with current X pointer
; Load XAR7 with start address of C array
; Load AR1 with size of data array N,
; Set product shift mode to ">> 4"
; Zero ACC, P, OVC
; Repeat next instruction N times
; ACC = ACC + P >> 4,
; P = (*AR6%++ * *XAR7++) >> 32
; Final accumulate
; Store XAR6 into current X pointer
; Store result into sum
15
AR1 X X
31
XAR6 X X X X X X
XAR6[7:0] is incremented until it matches AR1[7:0]
31
XAR6 X X X X
8 7 0
0 8
Buffer size = 8 + 1 = 9
8 7 0
0 0
Must be zero
8 7 0
X X 0 8
Matches AR1[7:0]