75 lines
2.1 KiB
C
75 lines
2.1 KiB
C
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/**
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* Copyright (C) 2009 Ubixum, Inc.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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**/
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#include <fx2regs.h>
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#include <fx2macros.h>
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#include <delay.h>
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void
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delay(WORD millis)
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{
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/**
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* It takes 12 crystal pulses to make 1 machine cycle (8051.com)
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* ez-usb trm 1.13
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* 83.3 ns at 48mhz per instruction cycle
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* (assume 166.6ns at 24mhz)
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* (assume 333.3ns at 12mhz)
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* ez-usb trm 12.1
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* Includes the cycles for each instruction
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**/
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WORD loop_count;
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volatile WORD count; // NOTE perhaps use different solutions w/ out volatile
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// set count to the number of times we need to
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// go around a loop for 1 millisecond
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// then do that loop millis times. (1000 us=1ms)
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// 48mhz: 1000 us / (17 cycles * 83.3 ns / cycle / 1000 ns/us) = 706
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// 24mhz: 353
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// 12mhz: 177
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// recalculate if the number of cycles changes
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// like if you change the loop below
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loop_count = CPUFREQ == CLK_12M ? 177 : CPUFREQ == CLK_24M ? 353 : 706;
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// sdcc generated assembly
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/* cycles code
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; delay.c:31: do {
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00101$:
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; delay.c:32: } while ( --count );
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2 dec _delay_count_1_1
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2 mov a,#0xff
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4 cjne a,_delay_count_1_1,00121$
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2 dec (_delay_count_1_1 + 1)
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00121$:
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2 mov a,_delay_count_1_1
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2 orl a,(_delay_count_1_1 + 1)
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3 jnz 00101$
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Total 17
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*/
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do {
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count = loop_count;
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do {
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} while (--count);
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} while (--millis);
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}
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