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3608c106 UH |
1 | /** |
2 | * Copyright (C) 2009 Ubixum, Inc. | |
3 | * | |
4 | * This library is free software; you can redistribute it and/or | |
5 | * modify it under the terms of the GNU Lesser General Public | |
6 | * License as published by the Free Software Foundation; either | |
7 | * version 2.1 of the License, or (at your option) any later version. | |
8 | * | |
9 | * This library is distributed in the hope that it will be useful, | |
10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
12 | * Lesser General Public License for more details. | |
13 | * | |
14 | * You should have received a copy of the GNU Lesser General Public | |
040a6eae | 15 | * License along with this library; if not, see <http://www.gnu.org/licenses/>. |
3608c106 UH |
16 | **/ |
17 | ||
18 | #include <fx2regs.h> | |
19 | #include <fx2macros.h> | |
20 | #include <delay.h> | |
21 | ||
22 | void delay(WORD millis) { | |
23 | /** | |
24 | * It takes 12 crystal pulses to make 1 machine cycle (8051.com) | |
25 | * ez-usb trm 1.13 | |
26 | * 83.3 ns at 48mhz per instruction cycle | |
27 | * (assume 166.6ns at 24mhz) | |
28 | * (assume 333.3ns at 12mhz) | |
29 | * ez-usb trm 12.1 | |
30 | * Includes the cycles for each instruction | |
31 | **/ | |
32 | WORD loop_count; | |
33 | volatile WORD count; // NOTE perhaps use different solutions w/ out volatile | |
34 | ||
35 | ||
36 | // set count to the number of times we need to | |
37 | // go around a loop for 1 millisecond | |
38 | ||
39 | // then do that loop millis times. (1000 us=1ms) | |
40 | ||
41 | // 48mhz: 1000 us / (17 cycles * 83.3 ns / cycle / 1000 ns/us) = 706 | |
42 | // 24mhz: 353 | |
43 | // 12mhz: 177 | |
44 | // recalculate if the number of cycles changes | |
45 | // like if you change the loop below | |
46 | loop_count = CPUFREQ == CLK_12M ? 177 : | |
47 | CPUFREQ == CLK_24M ? 353 : 706; | |
48 | ||
49 | // sdcc generated assembly | |
50 | /* cycles code | |
51 | ; delay.c:31: do { | |
52 | 00101$: | |
53 | ; delay.c:32: } while ( --count ); | |
54 | 2 dec _delay_count_1_1 | |
55 | 2 mov a,#0xff | |
56 | 4 cjne a,_delay_count_1_1,00121$ | |
57 | 2 dec (_delay_count_1_1 + 1) | |
58 | 00121$: | |
59 | 2 mov a,_delay_count_1_1 | |
60 | 2 orl a,(_delay_count_1_1 + 1) | |
61 | 3 jnz 00101$ | |
62 | ||
63 | Total 17 | |
64 | */ | |
65 | ||
66 | do { | |
67 | count = loop_count; | |
68 | do { | |
69 | } while ( --count ); | |
70 | } while ( --millis ); | |
71 | ||
72 | } |