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;throttle_multiply.asm
;
;********************************************************************************
;* mpy8u *
;* Second Level Subroutine *
;* *
;* Program from Atmel file avr200.asm *
;* *
;* Since the 25kHz pwm cycle is 64 clock cycles long, this subroutine *
;* requires just under 1 25kHz clock cycles. *
;* *
;* A single line was added which adds 3 to Cycle_count *
;* *
;* Inputs: HILOCAL1 and B_TEMPLOCAL *
;* *
;* Returns: HILOCAL1 x B_TEMPLOCAL = B_TEMPLOCAL1:B_TEMPLOCAL *
;* *
;* Changed: B_TEMPLOCAL2 *
;* *
;* Calls: Not allowed *
;********************************************************************************
HILOCAL1 mc8u ; multiplicand
B_TEMPLOCAL mp8u ; multiplier
B_TEMPLOCAL m8uL ; result Low byte
B_TEMPLOCAL1 m8uH ; result High byte
B_TEMPLOCAL2 mcnt8u ; loop counter
;<ATMEL ROUTINE>
;***************************************************************************
;*
;* "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
;<END ATMEL ROUTINE>
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