1 | /* |
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2 | * This routine initializes the MC68360 Periodic Interval Timer |
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3 | * |
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4 | * The PIT has rather poor resolution, but it is easy to set up |
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5 | * and requires no housekeeping once it is going. |
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6 | * |
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7 | * Based on the `gen68302' board support package, and covered by the |
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8 | * original distribution terms. |
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9 | * |
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10 | * W. Eric Norum |
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11 | * Saskatchewan Accelerator Laboratory |
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12 | * University of Saskatchewan |
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13 | * Saskatoon, Saskatchewan, CANADA |
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14 | * eric@skatter.usask.ca |
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15 | * |
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16 | * $Id$ |
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17 | */ |
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18 | |
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19 | /* |
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20 | * Input parameters: NONE |
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21 | * |
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22 | * Output parameters: NONE |
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23 | * |
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24 | * COPYRIGHT (c) 1989-1999. |
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25 | * On-Line Applications Research Corporation (OAR). |
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26 | * |
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27 | * The license and distribution terms for this file may be |
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28 | * found in the file LICENSE in this distribution or at |
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29 | * http://www.OARcorp.com/rtems/license.html. |
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30 | */ |
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31 | |
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32 | #include <stdlib.h> /* for atexit() */ |
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33 | #include <bsp.h> |
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34 | #include <rtems/libio.h> |
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35 | #include "m68360.h" |
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36 | |
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37 | #define CLOCK_VECTOR 120 |
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38 | #define CLOCK_IRQ_LEVEL 4 |
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39 | |
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40 | /* |
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41 | * Clock_driver_ticks is a monotonically increasing counter of the |
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42 | * number of clock ticks since the driver was initialized. |
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43 | */ |
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44 | volatile rtems_unsigned32 Clock_driver_ticks; |
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45 | |
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46 | /* |
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47 | * These are set by clock driver during its init |
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48 | */ |
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49 | |
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50 | rtems_device_major_number rtems_clock_major = ~0; |
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51 | rtems_device_minor_number rtems_clock_minor; |
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52 | |
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53 | char M360DefaultWatchdogFeeder = 1; |
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54 | |
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55 | /* |
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56 | * RTEMS and hardware have different notions of clock rate. |
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57 | */ |
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58 | static unsigned long rtems_nsec_per_tick; |
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59 | static unsigned long pit_nsec_per_tick; |
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60 | |
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61 | /* |
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62 | * Periodic interval timer interrupt handler |
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63 | */ |
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64 | |
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65 | rtems_isr |
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66 | Clock_isr (rtems_vector_number vector) |
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67 | { |
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68 | static unsigned long nsec; |
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69 | |
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70 | /* |
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71 | * See if it's really time for a `tick' |
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72 | */ |
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73 | nsec += pit_nsec_per_tick; |
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74 | if (nsec >= rtems_nsec_per_tick) { |
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75 | nsec -= rtems_nsec_per_tick; |
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76 | |
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77 | /* |
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78 | * Perform a dummy read of DPRAM. |
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79 | * This works around a bug in Rev. B of the 68360 |
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80 | */ |
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81 | m360.dpram0[0]; |
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82 | |
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83 | /* |
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84 | * Feed the watchdog |
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85 | * Application code can override this by |
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86 | * setting M360DefaultWatchdogFeeder to zero. |
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87 | */ |
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88 | if (M360DefaultWatchdogFeeder) { |
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89 | m360.swsr = 0x55; |
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90 | m360.swsr = 0xAA; |
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91 | } |
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92 | |
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93 | /* |
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94 | * Announce the clock tick |
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95 | */ |
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96 | Clock_driver_ticks++; |
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97 | rtems_clock_tick(); |
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98 | } |
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99 | } |
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100 | |
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101 | void |
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102 | Clock_exit (void) |
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103 | { |
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104 | /* |
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105 | * Turn off periodic interval timer |
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106 | */ |
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107 | m360.pitr &= ~0xFF; |
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108 | } |
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109 | |
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110 | static void |
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111 | Install_clock (rtems_isr_entry clock_isr) |
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112 | { |
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113 | int divisor; |
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114 | extern int m360_clock_rate; /* This should be somewhere in a config file */ |
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115 | unsigned long nsec_per_chip_tick = 1000000000 / m360_clock_rate; |
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116 | unsigned long nsec_per_pit_tick = 512 * nsec_per_chip_tick; |
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117 | |
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118 | Clock_driver_ticks = 0; |
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119 | /* |
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120 | * Choose periodic interval timer register value |
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121 | * The rate at which the periodic interval timer |
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122 | * can generate interrupts is almost certainly not |
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123 | * the same as desired by the BSP configuration. |
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124 | * Handle the difference by choosing the largest PIT |
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125 | * interval which is less than or equal to the RTEMS |
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126 | * interval and skipping some hardware interrupts. |
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127 | * To reduce the jitter in the calls to RTEMS the |
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128 | * hardware interrupt interval is never less than |
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129 | * the maximum non-prescaled value from the PIT. |
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130 | * |
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131 | * For a 25 MHz external clock the basic clock rate is |
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132 | * 40 nsec * 128 * 4 = 20.48 usec/tick |
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133 | */ |
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134 | |
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135 | rtems_nsec_per_tick = BSP_Configuration.microseconds_per_tick * 1000; |
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136 | divisor = rtems_nsec_per_tick / nsec_per_pit_tick; |
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137 | if (divisor >= 256) { |
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138 | divisor = 255; |
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139 | } else if (divisor == 0) { |
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140 | divisor = 1; |
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141 | } |
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142 | pit_nsec_per_tick = nsec_per_pit_tick * divisor; |
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143 | m360.pitr &= ~0x1FF; |
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144 | m360.picr = (CLOCK_IRQ_LEVEL << 8) | CLOCK_VECTOR; |
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145 | set_vector (clock_isr, CLOCK_VECTOR, 1); |
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146 | m360.pitr |= divisor; |
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147 | atexit (Clock_exit); |
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148 | } |
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149 | |
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150 | rtems_device_driver |
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151 | Clock_initialize( |
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152 | rtems_device_major_number major, |
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153 | rtems_device_minor_number minor, |
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154 | void *pargp |
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155 | ) |
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156 | { |
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157 | Install_clock (Clock_isr); |
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158 | |
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159 | /* |
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160 | * make major/minor avail to others such as shared memory driver |
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161 | */ |
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162 | rtems_clock_major = major; |
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163 | rtems_clock_minor = minor; |
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164 | |
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165 | return RTEMS_SUCCESSFUL; |
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166 | } |
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167 | |
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168 | rtems_device_driver Clock_control( |
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169 | rtems_device_major_number major, |
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170 | rtems_device_minor_number minor, |
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171 | void *pargp |
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172 | ) |
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173 | { |
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174 | rtems_unsigned32 isrlevel; |
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175 | rtems_libio_ioctl_args_t *args = pargp; |
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176 | |
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177 | if (args) { |
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178 | /* |
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179 | * This is hokey, but until we get a defined interface |
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180 | * to do this, it will just be this simple... |
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181 | */ |
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182 | if (args->command == rtems_build_name('I', 'S', 'R', ' ')) { |
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183 | Clock_isr( CLOCK_VECTOR); |
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184 | } |
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185 | else if (args->command == rtems_build_name('N', 'E', 'W', ' ')) { |
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186 | rtems_interrupt_disable( isrlevel ); |
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187 | (void) set_vector( args->buffer, CLOCK_VECTOR, 1 ); |
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188 | rtems_interrupt_enable( isrlevel ); |
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189 | } |
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190 | } |
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191 | return RTEMS_SUCCESSFUL; |
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192 | } |
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