; Time adjustment is calculated as a function of:
;	rollover - # clock cycles to rollover
;	required - # clock cycles desired
;	read|modify|write - time allowance to read counter, modify it to the
;		desired count, and write counter back
;	2 - two cycles are lost to resynchronization upon counter write back
;   time_adj = rollover - required + read|modify|write + 2
;;;

time_adj	equ	d'65536'-d'25000'+d'12'+2	

ten_ms	btfss	INTCON,TMR0IF	;test timer0 rollover flag
	bra	ten_ms		;... polling loop	

	movff	TMR0L,tmr0l_c	;read 16 bit counter
	movff	TMR0H,tmr0h_c	;get buffered high half 
	movlw	low time_adj	;add time adjustment
	addwf	tmr0l_c,F
	movlw	high time_adj
	addwfc	tmr0h_c,F	
	movff	tmr0h_c,TMR0H	;pre-load high half first
	movff	tmr0l_c,TMR0L	;write the 16 bit counter

	bcf	INTCON,TMR0IF	;clear timer0 rollover flag
	return			;and return