--- a/src/rtc.asm	Wed Apr 10 10:51:07 2019 +0200
+++ b/src/rtc.asm	Mon Jun 03 14:01:48 2019 +0200
@@ -1,6 +1,6 @@
 ;=============================================================================
 ;
-;   File rtc.asm													## V2.98c
+;   File rtc.asm                              combined next generation V3.02.1
 ;
 ;
 ;   Copyright (c) 2011, JD Gascuel, HeinrichsWeikamp, all right reserved.
@@ -16,68 +16,102 @@
 ;=============================================================================
 
 	global	rtc_init
+	global	rtc_set_rtc
 rtc_init:
-	movlw	.1
-	movwf	secs
-	movlw	.59
-	movwf	mins
-	movlw	.12
-	movwf	hours
-	movlw	.2
-	movwf	day
+	banksel	isr_backup			; select bank ISR data
+	movlw	.0
+	movwf	rtc_latched_secs
+	movlw	.0
+	movwf	rtc_latched_mins
 	movlw	.12
-	movwf	month
-	movlw	.17
-	movwf	year
-;	rcall	rtc_set_rtc			; writes mins,sec,hours,day,month and year to rtc module
-;	return
-
-	global	rtc_set_rtc
+	movwf	rtc_latched_hour
+	movlw	firmware_creation_day
+	movwf	rtc_latched_day
+	movlw	firmware_creation_month
+	movwf	rtc_latched_month
+	movlw	firmware_creation_year
+	movwf	rtc_latched_year
 rtc_set_rtc:
-	banksel 0xF16				; Addresses, F16h through F5Fh, are also used by SFRs, but are not part of the Access RAM.
-        movlw 	0x55
-	movwf 	EECON2
-	movlw 	0xAA
-	movwf 	EECON2
-	bsf 	RTCCFG,RTCWREN		; Unlock sequence for RTCWREN
-	bsf	RTCCFG,RTCPTR1
-	bsf	RTCCFG,RTCPTR0		; year
-	movff	year,WREG
-	rcall	rtc_dec2bcd			; IN: temp1 in WREG, OUT: WREG in BCD, also sets to bank16h!
+	banksel	isr_backup
+	movlw	d'24'				; safeguard hour
+	cpfslt	rtc_latched_hour
+	clrf	rtc_latched_hour
+	movlw	d'60'				; safeguard minutes
+	cpfslt	rtc_latched_mins
+	clrf	rtc_latched_mins
+	movlw	d'60'				; safeguard seconds
+	cpfslt	rtc_latched_secs
+	clrf	rtc_latched_secs
+	movlw	d'99'				; safeguard year
+	cpfslt	rtc_latched_year
+	movwf	rtc_latched_year
+	movlw	d'12'				; safeguard month
+	cpfslt	rtc_latched_month
+	movwf	rtc_latched_month
+
+	banksel	common				; select bank common
+	rcall	rtc_check_day		; safeguard day
+	bsf		block_rtc_access	; suspend the ISR from accessing the RTC
+
+
+	banksel	0xF16				; addresses F16h through F5Fh are also used by SFRs, but are not part of the access RAM
+
+	movlw	0x55				; | unlock sequence for RTCWREN, EECON2 is located in the access RAM
+	movwf	EECON2				; |
+	movlw	0xAA				; |
+	movwf	EECON2				; |
+	bsf		RTCCFG,RTCWREN		; RTC write unlock, must follow directly after above unlock sequence!
+	bsf		RTCCFG,RTCPTR1
+	bsf		RTCCFG,RTCPTR0
+	movff	rtc_latched_year,WREG
+	rcall	rtc_dec2bcd			; IN: WREG in decimal, OUT: WREG in BCD, also sets to bank16h!
 	movwf	RTCVALL				; year
 	movwf	RTCVALH				; dummy write
-	movff	day,WREG
-	rcall	rtc_dec2bcd			; IN: temp1 in WREG, OUT: WREG in BCD, also sets to bank16h!
-	movwf	RTCVALL				;day
-	movff	month,WREG
-	rcall	rtc_dec2bcd			; IN: temp1 in WREG, OUT: WREG in BCD, also sets to bank16h!
-	movwf	RTCVALH				;month
-	movff	hours,WREG
-	rcall	rtc_dec2bcd			; IN: temp1 in WREG, OUT: WREG in BCD, also sets to bank16h!
-	movwf	RTCVALL				;hours
+	movff	rtc_latched_day,WREG
+	rcall	rtc_dec2bcd			; IN: WREG in decimal, OUT: WREG in BCD, also sets to bank16h!
+	movwf	RTCVALL				; day
+	movff	rtc_latched_month,WREG
+	rcall	rtc_dec2bcd			; IN: WREG in decimal, OUT: WREG in BCD, also sets to bank16h!
+	movwf	RTCVALH				; month
+	movff	rtc_latched_hour,WREG
+	rcall	rtc_dec2bcd			; IN: WREG in decimal, OUT: WREG in BCD, also sets to bank16h!
+	movwf	RTCVALL				; hour
 	movlw	d'0'
-	rcall	rtc_dec2bcd			; IN: temp1 in WREG, OUT: WREG in BCD, also sets to bank16h!
-	movwf	RTCVALH				;weekday
-	movff	secs,WREG
-	rcall	rtc_dec2bcd			; IN: temp1 in WREG, OUT: WREG in BCD, also sets to bank16h!
-	movwf	RTCVALL				;secs
-	movff	mins,WREG
-	rcall	rtc_dec2bcd			; IN: temp1 in WREG, OUT: WREG in BCD, also sets to bank16h!
-	movwf	RTCVALH				;minutes
-	movlw 	0x55
-	movwf 	EECON2
-	movlw 	0xAA
-	movwf 	EECON2
-	bcf 	RTCCFG,RTCWREN		; Lock sequence for RTCWREN
+	rcall	rtc_dec2bcd			; IN: WREG in decimal, OUT: WREG in BCD, also sets to bank16h!
+	movwf	RTCVALH				; weekday
+	movff	rtc_latched_secs,WREG
+	rcall	rtc_dec2bcd			; IN: WREG in decimal, OUT: WREG in BCD, also sets to bank16h!
+	movwf	RTCVALL				; seconds
+	movff	rtc_latched_mins,WREG
+	rcall	rtc_dec2bcd			; IN: WREG in decimal, OUT: WREG in BCD, also sets to bank16h!
+	movwf	RTCVALH				; minutes
+
+	movlw	0x55				; | probably not needed when clearing RTCWREN
+	movwf	EECON2				; |
+	movlw	0xAA				; |
+	movwf	EECON2				; |
+	bcf		RTCCFG,RTCWREN		; lock sequence for RTCWREN
+
 	banksel	common
+
+	; update the "live" RTC variables to bridge the time until the ISR reads the updated data from the RTC
+	movff	rtc_latched_year, rtc_year
+	movff	rtc_latched_month,rtc_month
+	movff	rtc_latched_day,  rtc_day
+	movff	rtc_latched_hour, rtc_hour
+	movff	rtc_latched_mins, rtc_mins
+	movff	rtc_latched_secs, rtc_secs
+
+	bcf		block_rtc_access	; allow the ISR to access the RTC again
 	return
 
+
 rtc_dec2bcd:
-	banksel	lo
-	movwf	lo					; Input in decimal
+	banksel	common				; switch to bank common
+	movwf	lo					; input in decimal
 	setf	hi					; 10s
 rtc_dec2bcd2:
-	incf	hi,F				; Count 10's
+	incf	hi,F				; count 10's
 	movlw	d'10'
 	subwf	lo,F
 	btfss	STATUS,N
@@ -85,8 +119,49 @@
 	movlw	d'10'
 	addwf	lo,F				; 1s
 	swapf	hi,W				; swap to bit 7-4 -> WREG
-	addwf	lo,W				; Result in BCD
-	banksel	0xF16				; Addresses, F16h through F5Fh, are also used by SFRs, but are not part of the Access RAM
+	addwf	lo,W				; result in BCD
+	banksel	0xF16				; switch back to bank for I/O registers
 	return
 
-	END
\ No newline at end of file
+rtc_check_day:
+	movlw	.28					; the default February has 28 days
+	movff	rtc_latched_year,lo	; bank-safe get of the current year
+	btfsc	lo,0				; is the current year an even year?
+	bra		rtc_check_day_1		; NO
+	btfss	lo,1				; YES - is it a multiple of 4 years?
+	movlw	.29					;       YES - leap year, February has 29 days
+rtc_check_day_1:				;       NO  - keep the 28 days
+	movwf	hi					; store highest day in February in hi
+	movff	rtc_latched_month,lo; bank-safe get of the current month
+	dcfsnz	lo,F				; current month = January?
+	movlw	.31					; YES - highest day is 31
+	dcfsnz	lo,F				; current month = February?
+	movf	hi,W				; YES - highest day is 28/29
+	dcfsnz	lo,F				; current month = March?
+	movlw	.31					; YES - highest day is 31
+	dcfsnz	lo,F				; current month = April?
+	movlw	.30					; YES - highest day is 30
+	dcfsnz	lo,F				; current month = May?
+	movlw	.31					; YES - highest day is 31
+	dcfsnz	lo,F				; current month = June?
+	movlw	.30					; YES - highest day is 30
+	dcfsnz	lo,F				; current month = July?
+	movlw	.31					; YES - highest day is 31
+	dcfsnz	lo,F				; current month = August?
+	movlw	.31					; YES - highest day = 31
+	dcfsnz	lo,F				; current month = September?
+	movlw	.30					; YES - highest day = 30
+	dcfsnz	lo,F				; current month = October?
+	movlw	.31					; YES - highest day = 31
+	dcfsnz	lo,F				; current month = November?
+	movlw	.30					; YES - highest day = 30
+	dcfsnz	lo,F				; current month = December?
+	movlw	.31					; YES - highest day = 31
+	movff	rtc_latched_day,hi	; bank-safe get of the current day
+	cpfsgt	hi					; current day > highest day?
+	return						; NO  - day is ok
+	movlw	.1					; YES - wrap around to 1st day in month
+	movff	WREG,rtc_latched_day;     - bank-safe write-back of corrected day
+	return						;     - done
+
+	END