我们继续来看calc_next_comm_timing, 每次操作完换相之后，这里都会调用，同时会设置timer3去等advance timing.

总体思想是根据电机运行状态计算前4次换相时间，然后根据前4次换相时间计算15度和7.5度电角度时间，换相之后延时7.5度电角度开始检测过零点，检测到过零点后延时15度电角度进行换相.

视频

下图来自网络，我也没有清晰的，大家将就，原作者请@我，我加上版本信息。谢谢

;**** **** **** **** **** **** **** **** **** **** **** **** ****
;
; Calculate next commutation timing routine
;
; No assumptions
;
; Called immediately after each commutation
; Also sets up timer 3 to wait advance timing
; Two entry points are used
;
;**** **** **** **** **** **** **** **** **** **** **** **** ****
calc_next_comm_timing:		; Entry point for run phase
	; Read commutation time
	clr	IE_EA
	clr	TMR2CN0_TR2		; Timer 2 disabled
	mov	Temp1, TMR2L		; Load timer value
	mov	Temp2, TMR2H	    ;  temp1, temp2取timer2当时的计数
	mov	Temp3, Timer2_X     
	jnb	TMR2CN0_TF2H, ($+4)	; Check if interrupt is pending， 检查timer2的中断溢出标志要是零的话跳走，temp3不加1
	inc	Temp3			; If it is pending, then timer has already wrapped， 已经超时了，Temp3+1
	setb	TMR2CN0_TR2		; Timer 2 enabled， 打开timer.
	setb	IE_EA ;打开全部中断
IF MCU_48MHZ >= 1
	clr	C 
	mov	A, Temp3
	rrc	A          
	mov	Temp3, A   ;Temp3 = Temp3/2
	mov	A, Temp2
	rrc	A
	mov	Temp2, A   ;Temp2 = Temp2/2
	mov	A, Temp1
	rrc	A
	mov	Temp1, A    ;Temp1 = Temp1/2
ENDIF
	; Calculate this commutation time
	mov	Temp4, Prev_Comm_L      ; temp4/5 赋为上次操作时间
	mov	Temp5, Prev_Comm_H
	mov	Prev_Comm_L, Temp1		; Store timestamp as previous commutation
	mov	Prev_Comm_H, Temp2      ; 保存当前时间到上次操作时间到Pre_Comm_L/H
	clr	C
	mov	A, Temp1
	subb	A, Temp4				; Calculate the new commutation time
	mov	Temp1, A
	mov	A, Temp2
	subb	A, Temp5             ;当前时间减去上次时间，结果在temp1,和A.
	jb	Flags1.STARTUP_PHASE, calc_next_comm_startup ;如果启动阶段，跳走。

IF MCU_48MHZ >= 1          
	anl	A, #7Fh         ;如果48Mhz, 高位 & 7Fh
ENDIF
	mov	Temp2, A         ;保存高位到Temp2
	jnb	Flags1.HIGH_RPM, ($+5)	; Branch if high rpm ,
	ajmp	calc_next_comm_timing_fast ; 是高rpm，跳到calc_next_comm_timing_fast

	ajmp	calc_next_comm_normal  ； 如果不是高rpm，跳到calc_next_comm_normal

calc_next_comm_startup:
	mov	Temp6, Prev_Comm_X
	mov	Prev_Comm_X, Temp3		; Store extended timestamp as previous commutation
	mov	Temp2, A
	mov	A, Temp3
	subb	A, Temp6				; Calculate the new extended commutation time
IF MCU_48MHZ >= 1
	anl	A, #7Fh    ;如果48Mhz, 高位 & 7Fh
ENDIF
	mov	Temp3, A
	jz	calc_next_comm_startup_no_X

	mov	Temp1, #0FFh
	mov	Temp2, #0FFh
	ajmp	calc_next_comm_startup_average

calc_next_comm_startup_no_X:
	mov	Temp7, Prev_Prev_Comm_L
	mov	Temp8, Prev_Prev_Comm_H
	mov	Prev_Prev_Comm_L, Temp4
	mov	Prev_Prev_Comm_H, Temp5
	mov	Temp1, Prev_Comm_L		; Reload this commutation time	
	mov	Temp2, Prev_Comm_H
	clr	C
	mov	A, Temp1
	subb	A, Temp7				; Calculate the new commutation time based upon the two last commutations (to reduce sensitivity to offset)
	mov	Temp1, A
	mov	A, Temp2
	subb	A, Temp8
	mov	Temp2, A

calc_next_comm_startup_average:
	clr	C
	mov	A, Comm_Period4x_H		; Average with previous and save
	rrc	A
	mov	Temp4, A
	mov	A, Comm_Period4x_L
	rrc	A
	mov	Temp3, A
	mov	A, Temp1			
	add	A, Temp3
	mov	Comm_Period4x_L, A
	mov	A, Temp2
	addc	A, Temp4
	mov	Comm_Period4x_H, A
	jnc	($+8)

	mov	Comm_Period4x_L, #0FFh
	mov	Comm_Period4x_H, #0FFh

	ajmp	calc_new_wait_times_setup

calc_next_comm_normal:
	; Calculate new commutation time 
	mov	Temp3, Comm_Period4x_L	; Comm_Period4x(-l-h) holds the time of 4 commutations
	mov	Temp4, Comm_Period4x_H
	mov	Temp5, Comm_Period4x_L	; Copy variables
	mov	Temp6, Comm_Period4x_H
	mov	Temp7, #4				; Divide Comm_Period4x 4 times as default
	mov	Temp8, #2				; Divide new commutation time 2 times as default
	clr	C
	mov	A, Temp4
	subb	A, #04h
	jc	calc_next_comm_avg_period_div

	dec	Temp7				; Reduce averaging time constant for low speeds
	dec	Temp8

	clr	C
	mov	A, Temp4
	subb	A, #08h
	jc	calc_next_comm_avg_period_div

	jb	Flags1.INITIAL_RUN_PHASE, calc_next_comm_avg_period_div	; Do not average very fast during initial run

	dec	Temp7				; Reduce averaging time constant more for even lower speeds
	dec	Temp8

calc_next_comm_avg_period_div:
	clr	C
	mov	A, Temp6					
	rrc	A					; Divide by 2
	mov	Temp6, A	
	mov	A, Temp5				
	rrc	A
	mov	Temp5, A
	djnz	Temp7, calc_next_comm_avg_period_div

	clr	C
	mov	A, Temp3
	subb	A, Temp5				; Subtract a fraction
	mov	Temp3, A
	mov	A, Temp4
	subb	A, Temp6
	mov	Temp4, A
	mov	A, Temp8				; Divide new time
	jz	calc_next_comm_new_period_div_done

calc_next_comm_new_period_div:
	clr	C
	mov	A, Temp2					
	rrc	A					; Divide by 2
	mov	Temp2, A	
	mov	A, Temp1				
	rrc	A
	mov	Temp1, A
	djnz	Temp8, calc_next_comm_new_period_div

calc_next_comm_new_period_div_done:
	mov	A, Temp3
	add	A, Temp1				; Add the divided new time
	mov	Temp3, A
	mov	A, Temp4
	addc	A, Temp2
	mov	Temp4, A
	mov	Comm_Period4x_L, Temp3	; Store Comm_Period4x_X
	mov	Comm_Period4x_H, Temp4
	jnc	calc_new_wait_times_setup; If period larger than 0xffff - go to slow case

	mov	Temp4, #0FFh
	mov	Comm_Period4x_L, Temp4	; Set commutation period registers to very slow timing (0xffff)
	mov	Comm_Period4x_H, Temp4

calc_new_wait_times_setup:	
	; Set high rpm bit (if above 156k erpm)
	clr	C
	mov	A, Temp4
	subb	A, #2
	jnc	($+4)

	setb	Flags1.HIGH_RPM 		; Set high rpm bit
	
	; Load programmed commutation timing
	jnb	Flags1.STARTUP_PHASE, calc_new_wait_per_startup_done	; Set dedicated timing during startup

	mov	Temp8, #3
	ajmp	calc_new_wait_per_demag_done

calc_new_wait_per_startup_done:
	mov	Temp1, #Pgm_Comm_Timing	; Load timing setting
	mov	A, @Temp1				
	mov	Temp8, A				; Store in Temp8
	clr	C
	mov	A, Demag_Detected_Metric	; Check demag metric
	subb	A, #130
	jc	calc_new_wait_per_demag_done

	inc	Temp8				; Increase timing

	clr	C
	mov	A, Demag_Detected_Metric
	subb	A, #160
	jc	($+3)

	inc	Temp8				; Increase timing again

	clr	C
	mov	A, Temp8				; Limit timing to max
	subb	A, #6
	jc	($+4)

	mov	Temp8, #5				; Set timing to max

calc_new_wait_per_demag_done:
	; Set timing reduction
	mov	Temp7, #2
	; Load current commutation timing
	mov	A, Comm_Period4x_H		; Divide 4 times
	swap	A
	anl	A, #00Fh
	mov	Temp2, A
	mov	A, Comm_Period4x_H
	swap	A
	anl	A, #0F0h
	mov	Temp1, A
	mov	A, Comm_Period4x_L
	swap	A
	anl	A, #00Fh
	add	A, Temp1
	mov	Temp1, A

	clr	C
	mov	A, Temp1
	subb	A, Temp7
	mov	Temp3, A
	mov	A, Temp2				
	subb	A, #0
	mov	Temp4, A
	jc	load_min_time			; Check that result is still positive

	clr	C
	mov	A, Temp3
	subb	A, #1
	mov	A, Temp4			
	subb	A, #0
	jnc	calc_new_wait_times_exit	; Check that result is still above minumum

load_min_time:
	mov	Temp3, #1
	clr	A
	mov	Temp4, A 

calc_new_wait_times_exit:	
	ljmp	wait_advance_timing


; Fast calculation (Comm_Period4x_H less than 2)
calc_next_comm_timing_fast:			
	; Calculate new commutation time
	mov	Temp3, Comm_Period4x_L	; Comm_Period4x(-l-h) holds the time of 4 commutations
	mov	Temp4, Comm_Period4x_H
	mov	A, Temp4				; Divide by 2 4 times
	swap	A
	mov	Temp7, A
	mov	A, Temp3
	swap A
	anl	A, #0Fh
	orl	A, Temp7
	mov	Temp5, A
	clr	C
	mov	A, Temp3				; Subtract a fraction
	subb	A, Temp5
	mov	Temp3, A
	mov	A, Temp4				
	subb	A, #0
	mov	Temp4, A
	clr	C
	mov	A, Temp1
	rrc	A					; Divide by 2 2 times
	clr	C
	rrc	A
	mov	Temp1, A
	mov	A, Temp3				; Add the divided new time
	add	A, Temp1
	mov	Temp3, A
	mov	A, Temp4
	addc	A, #0
	mov	Temp4, A
	mov	Comm_Period4x_L, Temp3	; Store Comm_Period4x_X
	mov	Comm_Period4x_H, Temp4
	clr	C
	mov	A, Temp4				; If erpm below 156k - go to normal case
	subb	A, #2
	jc	($+4)

	clr	Flags1.HIGH_RPM 		; Clear high rpm bit

	; Set timing reduction
	mov	Temp1, #2
	mov	A, Temp4				; Divide by 2 4 times
	swap	A
	mov	Temp7, A
	mov	Temp4, #0
	mov	A, Temp3
	swap A
	anl	A, #0Fh
	orl	A, Temp7
	mov	Temp3, A
	clr	C
	mov	A, Temp3
	subb	A, Temp1
	mov	Temp3, A
	jc	load_min_time_fast		; Check that result is still positive

	clr	C
	subb	A, #1
	jnc	calc_new_wait_times_fast_done	; Check that result is still above minumum

load_min_time_fast:
	mov	Temp3, #1

calc_new_wait_times_fast_done:	
	mov	Temp1, #Pgm_Comm_Timing	; Load timing setting
	mov	A, @Temp1				
	mov	Temp8, A				; Store in Temp8


;**** **** **** **** **** **** **** **** **** **** **** **** ****
;
; Wait advance timing routine
;
; No assumptions
; NOTE: Be VERY careful if using temp registers. They are passed over this routine
;
; Waits for the advance timing to elapse and sets up the next zero cross wait
;
;**** **** **** **** **** **** **** **** **** **** **** **** ****
wait_advance_timing:	
	jnb	Flags0.T3_PENDING, ($+5)
	ajmp	wait_advance_timing

	; Setup next wait time
	mov	TMR3RLL, Wt_ZC_Tout_Start_L
	mov	TMR3RLH, Wt_ZC_Tout_Start_H
	setb	Flags0.T3_PENDING
	orl	EIE1, #80h	; Enable timer 3 interrupts


;**** **** **** **** **** **** **** **** **** **** **** **** ****
;
; Calculate new wait times routine
;
; No assumptions
;
; Calculates new wait times
;
;**** **** **** **** **** **** **** **** **** **** **** **** ****
calc_new_wait_times:	
	clr	C
	clr	A
	subb	A, Temp3				; Negate
	mov	Temp1, A	
	clr	A
	subb	A, Temp4				
	mov	Temp2, A	
IF MCU_48MHZ >= 1
	clr	C
	mov	A, Temp1				; Multiply by 2
	rlc	A
	mov	Temp1, A
	mov	A, Temp2
	rlc	A
	mov	Temp2, A
ENDIF
	jnb	Flags1.HIGH_RPM, ($+6)	; Branch if high rpm
	ljmp	calc_new_wait_times_fast

	mov	A, Temp1				; Copy values
	mov	Temp3, A
	mov	A, Temp2
	mov	Temp4, A
	setb	C					; Negative numbers - set carry
	mov	A, Temp2				
	rrc	A					; Divide by 2
	mov	Temp6, A
	mov	A, Temp1
	rrc	A
	mov	Temp5, A
	mov	Wt_Zc_Tout_Start_L, Temp1; Set 15deg time for zero cross scan timeout
	mov	Wt_Zc_Tout_Start_H, Temp2
	clr	C
	mov	A, Temp8				; (Temp8 has Pgm_Comm_Timing)
	subb	A, #3				; Is timing normal?
	jz	store_times_decrease	; Yes - branch

	mov	A, Temp8				
	jb	ACC.0, adjust_timing_two_steps	; If an odd number - branch

	mov	A, Temp1				; Add 7.5deg and store in Temp1/2
	add	A, Temp5
	mov	Temp1, A
	mov	A, Temp2
	addc	A, Temp6
	mov	Temp2, A
	mov	A, Temp5				; Store 7.5deg in Temp3/4
	mov	Temp3, A
	mov	A, Temp6			
	mov	Temp4, A
	jmp	store_times_up_or_down

adjust_timing_two_steps:
	mov	A, Temp1				; Add 15deg and store in Temp1/2
	add	A, Temp1
	mov	Temp1, A
	mov	A, Temp2
	addc	A, Temp2
	mov	Temp2, A
	clr	C
	mov	A, Temp1
	add	A, #1
	mov	Temp1, A
	mov	A, Temp2
	addc	A, #0
	mov	Temp2, A
	mov	Temp3, #-1				; Store minimum time in Temp3/4
	mov	Temp4, #0FFh

store_times_up_or_down:
	clr	C
	mov	A, Temp8				
	subb	A, #3					; Is timing higher than normal?
	jc	store_times_decrease		; No - branch

store_times_increase:
	mov	Wt_Comm_Start_L, Temp3		; Now commutation time (~60deg) divided by 4 (~15deg nominal)
	mov	Wt_Comm_Start_H, Temp4
	mov	Wt_Adv_Start_L, Temp1		; New commutation advance time (~15deg nominal)
	mov	Wt_Adv_Start_H, Temp2
	mov	Wt_Zc_Scan_Start_L, Temp5	; Use this value for zero cross scan delay (7.5deg)
	mov	Wt_Zc_Scan_Start_H, Temp6
	ljmp	wait_before_zc_scan

store_times_decrease:
	mov	Wt_Comm_Start_L, Temp1		; Now commutation time (~60deg) divided by 4 (~15deg nominal)
	mov	Wt_Comm_Start_H, Temp2
	mov	Wt_Adv_Start_L, Temp3		; New commutation advance time (~15deg nominal)
	mov	Wt_Adv_Start_H, Temp4
	mov	Wt_Zc_Scan_Start_L, Temp5	; Use this value for zero cross scan delay (7.5deg)
	mov	Wt_Zc_Scan_Start_H, Temp6
	jnb	Flags1.STARTUP_PHASE, store_times_exit

	mov	Wt_Comm_Start_L, #0F0h		; Set very short delays for all but advance time during startup, in order to widen zero cross capture range
	mov	Wt_Comm_Start_H, #0FFh
	mov	Wt_Zc_Scan_Start_L, #0F0h
	mov	Wt_Zc_Scan_Start_H, #0FFh
	mov	Wt_Zc_Tout_Start_L, #0F0h
	mov	Wt_Zc_Tout_Start_H, #0FFh

store_times_exit:
	ljmp	wait_before_zc_scan


calc_new_wait_times_fast:	
	mov	A, Temp1				; Copy values
	mov	Temp3, A
	setb	C					; Negative numbers - set carry
	mov	A, Temp1				; Divide by 2
	rrc	A
	mov	Temp5, A
	mov	Wt_Zc_Tout_Start_L, Temp1; Set 15deg time for zero cross scan timeout
	clr	C
	mov	A, Temp8				; (Temp8 has Pgm_Comm_Timing)
	subb	A, #3				; Is timing normal?
	jz	store_times_decrease_fast; Yes - branch

	mov	A, Temp8				
	jb	ACC.0, adjust_timing_two_steps_fast	; If an odd number - branch

	mov	A, Temp1				; Add 7.5deg and store in Temp1
	add	A, Temp5
	mov	Temp1, A
	mov	A, Temp5				; Store 7.5deg in Temp3
	mov	Temp3, A
	ajmp	store_times_up_or_down_fast

adjust_timing_two_steps_fast:
	mov	A, Temp1				; Add 15deg and store in Temp1
	add	A, Temp1
	add	A, #1
	mov	Temp1, A
	mov	Temp3, #-1			; Store minimum time in Temp3

store_times_up_or_down_fast:
	clr	C
	mov	A, Temp8				
	subb	A, #3				; Is timing higher than normal?
	jc	store_times_decrease_fast; No - branch

store_times_increase_fast:
	mov	Wt_Comm_Start_L, Temp3		; Now commutation time (~60deg) divided by 4 (~15deg nominal)
	mov	Wt_Adv_Start_L, Temp1		; New commutation advance time (~15deg nominal)
	mov	Wt_Zc_Scan_Start_L, Temp5	; Use this value for zero cross scan delay (7.5deg)
	ljmp	wait_before_zc_scan

store_times_decrease_fast:
	mov	Wt_Comm_Start_L, Temp1		; Now commutation time (~60deg) divided by 4 (~15deg nominal)
	mov	Wt_Adv_Start_L, Temp3		; New commutation advance time (~15deg nominal)
	mov	Wt_Zc_Scan_Start_L, Temp5	; Use this value for zero cross scan delay (7.5deg)


;**** **** **** **** **** **** **** **** **** **** **** **** ****
;
; Wait before zero cross scan routine
;
; No assumptions
;
; Waits for the zero cross scan wait time to elapse
; Also sets up timer 3 for the zero cross scan timeout time
;
;**** **** **** **** **** **** **** **** **** **** **** **** ****
wait_before_zc_scan:	
	jnb	Flags0.T3_PENDING, ($+5)  ;jump if Flags0.T3_PENDING is zero
	ajmp	wait_before_zc_scan

	mov	Startup_Zc_Timeout_Cntd, #2
setup_zc_scan_timeout:
	setb	Flags0.T3_PENDING
	orl	EIE1, #80h			; Enable timer 3 interrupts
	mov	A, Flags1
	anl	A, #((1 SHL STARTUP_PHASE)+(1 SHL INITIAL_RUN_PHASE))
	jz	wait_before_zc_scan_exit		

	mov	Temp1, Comm_Period4x_L	; Set long timeout when starting
	mov	Temp2, Comm_Period4x_H
	clr	C
	mov	A, Temp2
	rrc	A
	mov	Temp2, A
	mov	A, Temp1
	rrc	A
	mov	Temp1, A
IF MCU_48MHZ == 0
	clr	C
	mov	A, Temp2
	rrc	A
	mov	Temp2, A
	mov	A, Temp1
	rrc	A
	mov	Temp1, A
ENDIF
	jnb	Flags1.STARTUP_PHASE, setup_zc_scan_timeout_startup_done

	mov	A, Temp2
	add	A, #40h				; Increase timeout somewhat to avoid false wind up
	mov	Temp2, A

setup_zc_scan_timeout_startup_done:
	clr	IE_EA
	anl	EIE1, #7Fh			; Disable timer 3 interrupts
	mov	TMR3CN0, #00h			; Timer 3 disabled and interrupt flag cleared
	clr	C
	clr	A
	subb	A, Temp1				; Set timeout
	mov	TMR3L, A
	clr	A
	subb	A, Temp2		
	mov	TMR3H, A
	mov	TMR3CN0, #04h			; Timer 3 enabled and interrupt flag cleared
	setb	Flags0.T3_PENDING
	orl	EIE1, #80h			; Enable timer 3 interrupts
	setb	IE_EA

wait_before_zc_scan_exit:          
	ret