/**
 * Copyright (C) 2009 Ubixum, Inc. 
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 **/

#include <fx2regs.h>
#include <fx2macros.h>
#include <delay.h>

void
delay(WORD millis)
{
    /**
     * It takes 12 crystal pulses to make 1 machine cycle (8051.com)
     * ez-usb trm 1.13
     *  83.3 ns at 48mhz per instruction cycle
     *  (assume 166.6ns at 24mhz)
     *  (assume 333.3ns at 12mhz)
     * ez-usb trm 12.1
     *  Includes the cycles for each instruction
     **/
	WORD loop_count;
	volatile WORD count;	// NOTE perhaps use different solutions w/ out volatile


	// set count to the number of times we need to
	// go around a loop for 1 millisecond

	// then do that loop millis times. (1000 us=1ms)

	// 48mhz: 1000 us / (17 cycles * 83.3 ns / cycle / 1000 ns/us) = 706
	// 24mhz: 353
	// 12mhz: 177
	// recalculate if the number of cycles changes
	// like if you change the loop below
	loop_count = CPUFREQ == CLK_12M ? 177 : CPUFREQ == CLK_24M ? 353 : 706;

	// sdcc generated assembly
	/*  cycles   code
	   ;   delay.c:31: do {
	   00101$:
	   ;   delay.c:32: } while ( --count );
	   2           dec _delay_count_1_1
	   2           mov a,#0xff
	   4           cjne    a,_delay_count_1_1,00121$
	   2           dec (_delay_count_1_1 + 1)
	   00121$:
	   2           mov a,_delay_count_1_1
	   2           orl a,(_delay_count_1_1 + 1)
	   3           jnz 00101$

	   Total 17
	 */

	do {
		count = loop_count;
		do {
		} while (--count);
	} while (--millis);

}