Multiply 16x16 (Signed) array 8bit and then sum all to 3 bytes

main.asm

.macro lock
	push RA
	push RB
	push RC
	push RD
	push RE
	push RF
	push RI
	push RT
.endmacro 
.macro unlock
	pop RT
	pop RI
	pop RF
	pop RE
	pop RD
	pop RC
	pop RB
	pop RA
.endmacro

.def RA = R16
.def RB = R17
.def RC = R18
.def RD = R19
.def RE = R20
.def RF = R21
.def RI = R22
.def RT = R23
.equ A_ADDR = 0x100 // 16 items
.equ B_ADDR = 0x120 // 16 items
.equ MUL_ADDR = 0x140 // 32 items
.equ SUM_ADDR = 0x200 // result 3 Bytes
start:
	ldi RA, HIGH(RAMEND)
	ldi RB, HIGH(RAMEND)
	call LOAD_A
	call LOAD_B
	call MUL_AB
	call SUM_ALL

h: rjmp h

; load a from flash and then store into ram
LOAD_A:
	lock
	ldi ZH, HIGH(DATA_A<<1)
	ldi ZL, LOW(DATA_A<<1)
	ldi XH, HIGH(A_ADDR)
	ldi XL, LOW(A_ADDR)
	ldi RI, 16
LA:
	lpm RC, Z+
	st X+,RC
	dec RI
	brne LA
	unlock
	ret
LOAD_B:
	lock
	ldi ZH, HIGH(DATA_B<<1)
	ldi ZL, LOW(DATA_B<<1)
	ldi XH, HIGH(B_ADDR)
	ldi XL, LOW(B_ADDR)
	ldi RI, 16
LB:
	lpm RC, Z+
	st X+,RC
	dec RI
	brne LB
	unlock
	ret

MUL_AB:
	lock
	ldi RI, 16
	ldi XH, HIGH(A_ADDR)
	ldi XL, LOW(A_ADDR)
	ldi YH, HIGH(B_ADDR)
	ldi YL, LOW(B_ADDR)
	ldi ZH, HIGH(MUL_ADDR)
	ldi ZL, LOW(MUL_ADDR)
LMUL:
	ld RA, X+
	ld RB, Y+
	MULS RA,RB // --> [R1:R0]
	// @   R1 วาง R1 ก่อน
	// @+1 R0 วาง R0 ตาม
	st Z+, R1
	st Z+, R0
	dec RI
	brne LMUL
	unlock
	ret
; sum and store into @SUM_ADDR
SUM_ALL:
	lock
	clr RC
	clr RB
	clr RA
	; [RC:RB:RA] <--
	; [RF:RE:RD] @MUL_ADDR
	ldi RI, 16
	ldi XH, HIGH(MUL_ADDR)
	ldi XL, LOW(MUL_ADDR)
; load to RE(high byte), RD(low byte)
; guess RF
; then RA+RD, RB+RE+c, RC+RF+c
SUML:
	ld RE, X+
	ld RD, X+
	clr RF // init to 0x00

	; guess RF value from RE
	lsl RE
	brcc positive
	negative: ldi RF, 0xFF
	positive: nop 
	; [RF:RE:RD] done
	add RA, RD
	adc RB, RE
	adc RC, RF

	dec RI
	brne SUML
	// store result [RC:RB:RA]
	ldi YH, HIGH(SUM_ADDR)
	ldi YL, LOW(SUM_ADDR)
	st	  Y, RC 
	std Y+1, RB
	std Y+2, RA
	unlock
	ret

// mockup data
.org $777
;DATA_A: .DB -1,-2,-3,-4,-5,-6,-7,10,12,0xF,-11,12,13,14,0xFF
;DATA_B: .DB 1,2,3,-4,-5,-6,-7,10,12,0xF,-11,12,0,0,1
// easy to sum
DATA_A: .DB 0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F
DATA_B: .DB 0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F,0x7F