avr_200.asm

Collected AVR assembler code samples to learn assembler. I use it in my classes.

;**** A P P L I C A T I O N   N O T E   A V R 2 0 0 ************************
;*
;* Title:		Multiply and Divide Routines
;* Version:		1.1
;* Last updated:	97.07.04
;* Target:		AT90Sxxxx (All AVR Devices)
;*
;* Support E-mail:	[e-mail]
;* 
;* DESCRIPTION
;* This Application Note lists subroutines for the following
;* Muliply/Divide applications:
;*
;* 8x8 bit unsigned
;* 8x8 bit signed
;* 16x16 bit unsigned
;* 16x16 bit signed
;* 8/8 bit unsigned
;* 8/8 bit signed
;* 16/16 bit unsigned
;* 16/16 bit signed
;*
;* All routines are Code Size optimized implementations
;*
;***************************************************************************

.include "1200def.inc"

	rjmp	RESET	;reset handle


;***************************************************************************
;*
;* "mpy8u" - 8x8 Bit Unsigned Multiplication
;*
;* This subroutine multiplies the two register variables mp8u and mc8u.
;* The result is placed in registers m8uH, m8uL
;*  
;* Number of words	:9 + return
;* Number of cycles	:58 + return
;* Low registers used	:None
;* High registers used  :4 (mp8u,mc8u/m8uL,m8uH,mcnt8u)	
;*
;* Note: Result Low byte and the multiplier share the same register.
;* This causes the multiplier to be overwritten by the result.
;*
;***************************************************************************

;***** Subroutine Register Variables

.def	mc8u	=r16		;multiplicand
.def	mp8u	=r17		;multiplier
.def	m8uL	=r17		;result Low byte
.def	m8uH	=r18		;result High byte
.def	mcnt8u	=r19		;loop counter

;***** Code


mpy8u:	clr	m8uH		;clear result High byte
	ldi	mcnt8u,8	;init loop counter
	lsr	mp8u		;rotate multiplier
	
m8u_1:	brcc	m8u_2		;carry set 
	add 	m8uH,mc8u	;   add multiplicand to result High byte
m8u_2:	ror	m8uH		;rotate right result High byte
	ror	m8uL		;rotate right result L byte and multiplier
	dec	mcnt8u		;decrement loop counter
	brne	m8u_1		;if not done, loop more
	ret




;***************************************************************************
;*
;* "mpy8s" - 8x8 Bit Signed Multiplication
;*
;* This subroutine multiplies signed the two register variables mp8s and 
;* mc8s. The result is placed in registers m8sH, m8sL
;* The routine is an implementation of Booth's algorithm. If all 16 bits
;* in the result are needed, avoid calling the routine with
;* -128 ($80) as multiplicand
;*  
;* Number of words	:10 + return
;* Number of cycles	:73 + return
;* Low registers used	:None
;* High registers used  :4 (mc8s,mp8s/m8sL,m8sH,mcnt8s)	
;*
;***************************************************************************

;***** Subroutine Register Variables

.def	mc8s	=r16		;multiplicand
.def	mp8s	=r17		;multiplier
.def	m8sL	=r17		;result Low byte
.def	m8sH	=r18		;result High byte
.def	mcnt8s	=r19		;loop counter

;***** Code

mpy8s:	sub	m8sH,m8sH	;clear result High byte and carry
	ldi	mcnt8s,8	;init loop counter
m8s_1:	brcc	m8s_2		;if carry (previous bit) set
	add	m8sH,mc8s	;    add multiplicand to result High byte
m8s_2:	sbrc	mp8s,0		;if current bit set
	sub	m8sH,mc8s	;    subtract multiplicand from result High
	asr	m8sH		;shift right result High byte
	ror	m8sL		;shift right result L byte and multiplier
	dec	mcnt8s		;decrement loop counter
	brne	m8s_1		;if not done, loop more
	ret



;***************************************************************************
;*
;* "mpy16u" - 16x16 Bit Unsigned Multiplication
;*
;* This subroutine multiplies the two 16-bit register variables 
;* mp16uH:mp16uL and mc16uH:mc16uL.
;* The result is placed in m16u3:m16u2:m16u1:m16u0.
;*  
;* Number of words	:14 + return
;* Number of cycles	:153 + return
;* Low registers used	:None
;* High registers used  :7 (mp16uL,mp16uH,mc16uL/m16u0,mc16uH/m16u1,m16u2,
;*                          m16u3,mcnt16u)	
;*
;***************************************************************************

;***** Subroutine Register Variables

.def	mc16uL	=r16		;multiplicand low byte
.def	mc16uH	=r17		;multiplicand high byte
.def	mp16uL	=r18		;multiplier low byte
.def	mp16uH	=r19		;multiplier high byte
.def	m16u0	=r18		;result byte 0 (LSB)
.def	m16u1	=r19		;result byte 1
.def	m16u2	=r20		;result byte 2
.def	m16u3	=r21		;result byte 3 (MSB)
.def	mcnt16u	=r22		;loop counter

;***** Code

mpy16u:	clr	m16u3		;clear 2 highest bytes of result
	clr	m16u2
	ldi	mcnt16u,16	;init loop counter
	lsr	mp16uH
	ror	mp16uL

m16u_1:	brcc	noad8		;if bit 0 of multiplier set
	add	m16u2,mc16uL	;add multiplicand Low to byte 2 of res
	adc	m16u3,mc16uH	;add multiplicand high to byte 3 of res
noad8:	ror	m16u3		;shift right result byte 3
	ror	m16u2		;rotate right result byte 2
	ror	m16u1		;rotate result byte 1 and multiplier High
	ror	m16u0		;rotate result byte 0 and multiplier Low
	dec	mcnt16u		;decrement loop counter
	brne	m16u_1		;if not done, loop more
	ret



;***************************************************************************
;*
;* "mpy16s" - 16x16 Bit Signed Multiplication
;*
;* This subroutine multiplies signed the two 16-bit register variables 
;* mp16sH:mp16sL and mc16sH:mc16sL.
;* The result is placed in m16s3:m16s2:m16s1:m16s0.
;* The routine is an implementation of Booth's algorithm. If all 32 bits
;* in the result are needed, avoid calling the routine with
;* -32768 ($8000) as multiplicand
;*  
;* Number of words	:16 + return
;* Number of cycles	:210/226 (Min/Max) + return
;* Low registers used	:None
;* High registers used  :7 (mp16sL,mp16sH,mc16sL/m16s0,mc16sH/m16s1,
;*			    m16s2,m16s3,mcnt16s)	
;*
;***************************************************************************

;***** Subroutine Register Variables

.def	mc16sL	=r16		;multiplicand low byte
.def	mc16sH	=r17		;multiplicand high byte
.def	mp16sL	=r18		;multiplier low byte
.def	mp16sH	=r19		;multiplier high byte
.def	m16s0	=r18		;result byte 0 (LSB)
.def	m16s1	=r19		;result byte 1
.def	m16s2	=r20		;result byte 2
.def	m16s3	=r21		;result byte 3 (MSB)
.def	mcnt16s	=r22		;loop counter

;***** Code
mpy16s:	clr	m16s3		;clear result byte 3
	sub	m16s2,m16s2	;clear result byte 2 and carry
	ldi	mcnt16s,16	;init loop counter
m16s_1:	brcc	m16s_2		;if carry (previous bit) set
	add	m16s2,mc16sL	;    add multiplicand Low to result byte 2
	adc	m16s3,mc16sH	;    add multiplicand High to result byte 3
m16s_2:	sbrc	mp16sL,0	;if current bit set
	sub	m16s2,mc16sL	;    sub multiplicand Low from result byte 2
	sbrc	mp16sL,0	;if current bit set
	sbc	m16s3,mc16sH	;    sub multiplicand High from result byte 3
	asr	m16s3		;shift right result and multiplier
	ror	m16s2
	ror	m16s1
	ror	m16s0
	dec	mcnt16s		;decrement counter
	brne	m16s_1		;if not done, loop more	
	ret



;***************************************************************************
;*
;* "div8u" - 8/8 Bit Unsigned Division
;*
;* This subroutine divides the two register variables "dd8u" (dividend) and 
;* "dv8u" (divisor). The result is placed in "dres8u" and the remainder in
;* "drem8u".
;*  
;* Number of words	:14
;* Number of cycles	:97
;* Low registers used	:1 (drem8u)
;* High registers used  :3 (dres8u/dd8u,dv8u,dcnt8u)
;*
;***************************************************************************

;***** Subroutine Register Variables

.def	drem8u	=r15		;remainder
.def	dres8u	=r16		;result
.def	dd8u	=r16		;dividend
.def	dv8u	=r17		;divisor
.def	dcnt8u	=r18		;loop counter

;***** Code

div8u:	sub	drem8u,drem8u	;clear remainder and carry
	ldi	dcnt8u,9	;init loop counter
d8u_1:	rol	dd8u		;shift left dividend
	dec	dcnt8u		;decrement counter
	brne	d8u_2		;if done
	ret			;    return
d8u_2:	rol	drem8u		;shift dividend into remainder
	sub	drem8u,dv8u	;remainder = remainder - divisor
	brcc	d8u_3		;if result negative
	add	drem8u,dv8u	;    restore remainder
	clc			;    clear carry to be shifted into result
	rjmp	d8u_1		;else
d8u_3:	sec			;    set carry to be shifted into result
	rjmp	d8u_1



;***************************************************************************
;*
;* "div8s" - 8/8 Bit Signed Division