75 lines
3.4 KiB
NASM
75 lines
3.4 KiB
NASM
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;throttle_multiply.asm
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;
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;********************************************************************************
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;* mpy8u *
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;* Second Level Subroutine *
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;* *
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;* Program from Atmel file avr200.asm *
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;* *
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;* Since the 25kHz pwm cycle is 64 clock cycles long, this subroutine *
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;* requires just under 1 25kHz clock cycles. *
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;* *
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;* A single line was added which adds 3 to Cycle_count *
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;* *
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;* Inputs: HILOCAL1 and B_TEMPLOCAL *
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;* *
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;* Returns: HILOCAL1 x B_TEMPLOCAL = B_TEMPLOCAL1:B_TEMPLOCAL *
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;* *
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;* Changed: B_TEMPLOCAL2 *
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;* *
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;* Calls: Not allowed *
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;********************************************************************************
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HILOCAL1 mc8u ; multiplicand
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B_TEMPLOCAL mp8u ; multiplier
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B_TEMPLOCAL m8uL ; result Low byte
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B_TEMPLOCAL1 m8uH ; result High byte
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B_TEMPLOCAL2 mcnt8u ; loop counter
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;<ATMEL ROUTINE>
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;***************************************************************************
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;*
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;* "mpy8u" - 8x8 Bit Unsigned Multiplication
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;*
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;* This subroutine multiplies the two register variables mp8u and mc8u.
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;* The result is placed in registers m8uH, m8uL
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;*
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;* Number of words :9 + return
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;* Number of cycles :58 + return
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;* Low registers used :None
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;* High registers used :4 (mp8u,mc8u/m8uL,m8uH,mcnt8u)
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;*
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;* Note: Result Low byte and the multiplier share the same register.
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;* This causes the multiplier to be overwritten by the result.
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;*
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;***************************************************************************
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;***** Subroutine Register Variables
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;.def mc8u =r16 ;multiplicand
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;.def mp8u =r17 ;multiplier
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;.def m8uL =r17 ;result Low byte
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;.def m8uH =r18 ;result High byte
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;.def mcnt8u =r19 ;loop counter
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;***** Code
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mpy8u:
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clr m8uH ;clear result High byte
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ldi mcnt8u,8 ;init loop counter
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lsr mp8u ;rotate multiplier
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m8u_1:
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brcc m8u_2 ;carry set
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add m8uH,mc8u ;add multiplicand to result High byte
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m8u_2:
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ror m8uH ;rotate right result High byte
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ror m8uL ;rotate right result L byte and multiplier
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dec mcnt8u ;decrement loop counter
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brne m8u_1 ;if not done, loop more
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ret
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;<END ATMEL ROUTINE>
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