1 | /* timer.c |
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2 | * |
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3 | * This file manages the interval timer on the PowerPC MPC821. |
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4 | * NOTE: This is not the PIT, but rather the RTEMS interval |
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5 | * timer |
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6 | * We shall use the bottom 32 bits of the timebase register, |
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7 | * |
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8 | * The following was in the 403 version of this file. I don't |
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9 | * know what it means. JTM 5/19/98 |
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10 | * NOTE: It is important that the timer start/stop overhead be |
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11 | * determined when porting or modifying this code. |
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12 | * |
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13 | * Author: Jay Monkman (jmonkman@frasca.com) |
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14 | * Copywright (C) 1998 by Frasca International, Inc. |
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15 | * |
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16 | * Derived from c/src/lib/libcpu/ppc/ppc403/timer/timer.c: |
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17 | * |
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18 | * Author: Andrew Bray <andy@i-cubed.co.uk> |
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19 | * |
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20 | * COPYRIGHT (c) 1995 by i-cubed ltd. |
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21 | * |
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22 | * To anyone who acknowledges that this file is provided "AS IS" |
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23 | * without any express or implied warranty: |
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24 | * permission to use, copy, modify, and distribute this file |
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25 | * for any purpose is hereby granted without fee, provided that |
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26 | * the above copyright notice and this notice appears in all |
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27 | * copies, and that the name of i-cubed limited not be used in |
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28 | * advertising or publicity pertaining to distribution of the |
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29 | * software without specific, written prior permission. |
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30 | * i-cubed limited makes no representations about the suitability |
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31 | * of this software for any purpose. |
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32 | * |
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33 | * Derived from c/src/lib/libcpu/hppa1_1/timer/timer.c: |
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34 | * |
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35 | * COPYRIGHT (c) 1989-1998. |
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36 | * On-Line Applications Research Corporation (OAR). |
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37 | * Copyright assigned to U.S. Government, 1994. |
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38 | * |
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39 | * The license and distribution terms for this file may be |
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40 | * found in the file LICENSE in this distribution or at |
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41 | * http://www.OARcorp.com/rtems/license.html. |
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42 | * |
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43 | * $Id$ |
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44 | */ |
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45 | |
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46 | #include <bsp.h> |
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47 | #include <rtems.h> |
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48 | #include <mpc821.h> |
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49 | |
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50 | extern rtems_cpu_table Cpu_table; /* owned by BSP */ |
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51 | |
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52 | static volatile rtems_unsigned32 Timer_starting; |
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53 | static rtems_boolean Timer_driver_Find_average_overhead; |
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54 | |
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55 | /* |
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56 | * This is so small that this code will be reproduced where needed. |
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57 | */ |
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58 | static inline rtems_unsigned32 get_itimer(void) |
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59 | { |
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60 | rtems_unsigned32 ret; |
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61 | |
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62 | asm volatile ("mftb %0" : "=r" ((ret))); /* TBLO */ |
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63 | |
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64 | return ret; |
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65 | } |
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66 | |
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67 | void Timer_initialize(void) |
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68 | { |
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69 | /* set interrupt level and enable timebase. This should never */ |
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70 | /* generate an interrupt however. */ |
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71 | m821.tbscr |= M821_TBSCR_TBIRQ(4) | M821_TBSCR_TBE; |
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72 | |
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73 | Timer_starting = get_itimer(); |
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74 | } |
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75 | |
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76 | int Read_timer(void) |
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77 | { |
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78 | rtems_unsigned32 clicks; |
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79 | rtems_unsigned32 total; |
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80 | |
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81 | clicks = get_itimer(); |
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82 | |
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83 | total = clicks - Timer_starting; |
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84 | |
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85 | if ( Timer_driver_Find_average_overhead == 1 ) |
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86 | return total; /* in XXX microsecond units */ |
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87 | |
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88 | else { |
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89 | if ( total < Cpu_table.timer_least_valid ) { |
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90 | return 0; /* below timer resolution */ |
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91 | } |
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92 | return (total - Cpu_table.timer_average_overhead); |
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93 | } |
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94 | } |
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95 | |
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96 | rtems_status_code Empty_function(void) |
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97 | { |
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98 | return RTEMS_SUCCESSFUL; |
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99 | } |
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100 | |
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101 | void Set_find_average_overhead(rtems_boolean find_flag) |
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102 | { |
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103 | Timer_driver_Find_average_overhead = find_flag; |
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104 | } |
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