Circular Buffer With Amode - Texas Instruments TMS320C28x Reference Manual

Indirect Addressing Modes
Figure 5−2. Circular Buffer with AMODE = 1
Top of buffer
Bottom of buffer
Example(s):
; Calculate FIR filter (X[N] = data array, C[N] = coefficientv array):
MOVW DP,#Xindex
MOVL XAR6,#X
MOV @AH,#N
MOV AL,@Xindex
MOVL XAR1,@ACC
MOVL XAR7,#C
SPM −4
ZAPA
RPT #N−1
||QMACL P,*+XAR6[AR1%++],*XAR7++
ADDL ACC,P << PM
MOV @Xindex,AR1
MOVL @Sum,ACC
5-24
31
XAR1 0 0 0 9
Buffer size =
9 + 1 = 10
31
XAR6 003F8010
XAR6 + XAR1[15:0] = 3F8010h
0x0000
XAR1[15:0] increments until
it matches XAR1[31:16]
XAR6 + XAR1[15:0] = 3F8010h + 0009h
Matches
XAR1[31:16]
; Load DP with page address of Xindex
; Load XAR6 with start address of X array
; Load AH with size of array X (N)
; Load AL with current circular index
; Load parameters into XAR1
; Load XAR7 with start address of C array
; 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 AR1 into current X index
; Store result into sum
16 15 0
0 0 0 0
Buffer index
0