AVR small stuff

ASM

jump table

assumed the CPU supports the required commands
all in CSEG :


;executes indexed (R15) procedure
execproc:
	PushY
	PushZ
	Push	R16

	SetZPtr	(jumptable*2)	; word adressing to byte adressing
	lsl	R15		; word adressing to byte adressing
	add	ZL		; add base and offset
	clr	R16
	adc	ZH,R16
	lpm
	mov	YL,R0		; the lsb of the adress to YL
	adiw	ZL,1
	lpm
	mov	YH,R0		; the msb of the adress to YH
	CopyYtoZ		; icall works through Z
	icall			; execute the selected procedure

	pop	R16
	PopZ
	PopY
	ret
	
	

jumptable:
proc0:	.dw	proc0
proc1:	.dw	proc1
proc2:	.dw	proc2
..

proc0:	; the proc0
	..
	ret

proc1:	; the proc1
	..
	ret

proc2:	; the proc2
	..
	ret

less than 10bit to BCD

 assume U1..U3 as R16..R31

; word U2,U3 msb to BCD at Z^ - 2 decimals
;   366 -> 36.60
;   127 -> 12.70
;   37  -> 03.70
;   15  -> 01.50
w2BCD3A:
	PushY
	Push	U1
	push	u2		; preserve input
	push	u3
	mov	YL,U2
	mov	YH,U3
	clr	U1		; loop counter
	ldi	u2,0x64		; 100 per digit
	ldi	u3,0
_w2l1:	inc	u1
	sub	YL,u2
	sbc	YH,u3
	brcc	_w2l1		; subtract until below zero
	add	YL,u2
	adc	YH,u3		; reverse to above zero
	dec	u1
	ori	u1,0x30		; make ASCII
	st	Z+,u1		; store
	clr	U1		; loop counter
_w2l2:	inc	u1
	sbiw	Yl,10		; 10 per digit
	brcc	_w2l2		; subtract until below zero
	adiw	YL,10		; reverse to above zero
	dec	u1
	ori	u1,0x30		; make ASCII
	st	Z+,u1		; store
	ldi	u1,'.'		
	st	Z+,u1		; decimal dot
	mov	u1,yl		; reminder as ones
	ori	u1,0x30
	st	Z+,u1
	ldi	u1,0x30		; append ASCII zero
	st	Z+,u1
	pop	u3
	pop	u2
	pop	U1
	popY
	ret

send byte - no irq, queueable

Sendbyte:	; u1 is byte
	out	UDR,u1
	nop
	nop
sb2:	sbis	USR,UDRE	; wait till out
 	rjmp	sb2
sb3:	sbis	USR,TXC		;wait for last bit out
	rjmp	sb3
	ret

compares as from p14-7

 assumes the compare as cp, cpi, cp16, cpi16, the last two to be seen
 on my macro page, or Appnote 202
 
 cpXX(Rd,Rr)
 BRXX as below

signed

compare			mnemo	cp - para
 Rd >  Rr		BRLT	Rr,Rd (swap)
 Rd >= Rr		BRGE	Rd,Rr
 Rd =  Rr		BREQ	Rd,Rr
 Rd <= Rr		BRGE	Rr,Rd (swap)
 Rd <  Rr		BRLT	Rd,Rr

unsigned

compare			mnemo	cp - para
 Rd >  Rr		BRLO	Rr,Rd (swap)
 Rd >= Rr		BRCC	Rd,Rr
 Rd =  Rr		BREQ	Rd,Rr
 Rd <= Rr		BRSH	Rr,Rd (swap)
 Rd <  Rr		BRLO	Rd,Rr

eg 	'skip if (U1 >= 0x10)' becomes when unsigned byte

	cpi	U1,0x10
	brcc	_next

eg	'skip if (U1 <= 0x10)' becomes when unsigned byte

	ldi	U2,0x10		; cannot be constant compare - use reg
	cp	U2,U1
	brsh	_next

other tricks

addi(byte) = subi(0xFF-byte+1)	; addi does not exist, but subi does

 



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last updated: 1.jan.00










Copyright (99,2001) Ing.Büro R.Tschaggelar