fx2/firmware/lib/delay.c

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2013-10-02 10:43:54 +02:00
/**
* 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);
}