1 | @c |
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2 | @c COPYRIGHT (c) 1988-1998. |
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3 | @c On-Line Applications Research Corporation (OAR). |
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4 | @c All rights reserved. |
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5 | @c |
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6 | @c $Id$ |
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7 | @c |
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8 | |
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9 | @chapter Target Dependent Files |
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10 | |
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11 | RTEMS has a multi-layered approach to portability. This is done to |
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12 | maximize the amount of software that can be reused. Much of the |
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13 | RTEMS source code can be reused on all RTEMS platforms. Other parts |
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14 | of the executive are specific to hardware in some sense. |
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15 | RTEMS classifies target dependent code based upon its dependencies |
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16 | into one of the following categories. |
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17 | |
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18 | @itemize @bullet |
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19 | @item CPU dependent |
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20 | @item Board dependent |
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21 | @item Peripheral dependent |
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22 | @end itemize |
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23 | |
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24 | @section CPU Dependent |
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25 | |
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26 | This class of code includes the foundation |
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27 | routines for the executive proper such as the context switch and |
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28 | the interrupt subroutine implementations. Sources for the supported |
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29 | processor families can be found in @code{c/src/exec/score/cpu}. |
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30 | A good starting point for a new family of processors is the |
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31 | @code{no_cpu} directory, which holds both prototypes and |
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32 | descriptions of each needed CPU dependent function. |
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33 | |
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34 | CPU dependent code is further subcategorized if the implementation is |
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35 | dependent on a particular CPU model. For example, the MC68000 and MC68020 |
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36 | processors are both members of the m68k CPU family but there are significant |
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37 | differents between these CPU models which RTEMS must take into account. |
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38 | |
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39 | @section Board Dependent |
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40 | |
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41 | This class of code provides the most specific glue between RTEMS and |
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42 | a particular board. This code is represented by the Board Support Packages |
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43 | and associated Device Drivers. Sources for the BSPs included in the |
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44 | RTEMS distribution are located in the directory @code{c/src/lib/libbsp}. |
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45 | The BSP source directory is further subdivided based on the CPU family |
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46 | and BSP. |
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47 | |
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48 | Some BSPs may support multiple board models within a single board family. |
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49 | This is necessary when the board supports multiple variants on a |
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50 | single base board. For example, the Motorola MVME162 board family has a |
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51 | fairly large number of variations based upon the particular CPU model |
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52 | and the peripherals actually placed on the board. |
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53 | |
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54 | @section Peripheral Dependent |
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55 | |
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56 | This class of code provides a reusable library of peripheral device |
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57 | drivers which can be tailored easily to a particular board. The |
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58 | libchip library is a collection of reusable software objects that |
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59 | correspond to standard controllers. Just as the hardware engineer |
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60 | chooses a standard controller when designing a board, the goal of |
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61 | this library is to let the software engineer do the same thing. |
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62 | |
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63 | The source code for the reusable peripheral driver library may be found |
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64 | in the directory @code{c/src/lib/libchip}. The source code is further |
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65 | divided based upon the class of hardware. Example classes include serial |
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66 | communications controllers, real-time clocks, non-volatile memory, and |
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67 | network controllers. |
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68 | |
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69 | @section Questions to Ask |
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70 | |
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71 | When evaluating what is required to support RTEMS applications on |
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72 | a particular target board, the following questions should be asked: |
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73 | |
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74 | @itemize @bullet |
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75 | |
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76 | @item Does a BSP for this board exist? |
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77 | |
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78 | @item Does a BSP for a similar board exists? |
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79 | |
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80 | @item Is the board's CPU supported? |
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81 | |
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82 | @end itemize |
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83 | |
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84 | If there is already a BSP for the board, then things may already be ready |
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85 | to start developing application software. All that remains is to verify |
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86 | that the existing BSP provides device drivers for all the peripherals |
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87 | on the board that the application will be using. For example, the application |
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88 | in question may require that the board's Ethernet controller be used and |
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89 | the existing BSP may not support this. |
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90 | |
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91 | If the BSP does not exist and the board's CPU model is supported, then |
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92 | examine the reusable chip library and existing BSPs for a close match. |
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93 | Other BSPs and libchip provide starting points for the development |
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94 | of a new BSP. It is often possible to copy existing components in |
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95 | the reusable chip library or device drivers from BSPs from different |
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96 | CPU families as the starting point for a new device driver. |
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97 | This will help reduce the development effort required. |
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98 | |
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99 | If the board's CPU family is supported but the particular CPU model on |
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100 | that board is not, then the RTEMS port to that CPU family will have to |
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101 | be augmented. After this is done, development of the new BSP can proceed. |
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102 | |
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103 | Otherwise both CPU dependent code and the BSP will have to be written. |
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104 | |
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105 | Regardless of the amount of development required, OAR Corporation |
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106 | offers custom development services to assist RTEMS users. |
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107 | For more information on custom development, training courses, and |
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108 | support, contact OAR Corporation at |
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109 | @uref{http://www.oarcorp.com}. |
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110 | |
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111 | |
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112 | @section CPU Dependent Executive Files |
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113 | |
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114 | The CPU dependent files in the RTEMS executive source code are found |
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115 | in the following directory: |
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116 | |
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117 | @example |
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118 | c/src/exec/score/cpu/@i{CPU} |
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119 | @end example |
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120 | |
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121 | where @i{CPU} is replaced with the CPU family name. |
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122 | |
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123 | Within each CPU dependent directory inside the executive proper is a |
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124 | file named @code{@i{CPU}.h} which contains information about each of the |
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125 | supported CPU models within that family. |
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126 | |
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127 | @section CPU Dependent Support Files |
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128 | |
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129 | The CPU dependent support files contain routines which aid in the development |
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130 | of applications using that CPU family. For example, the support routines |
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131 | may contain standard trap handlers for alignment or floating point exceptions |
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132 | or device drivers for peripheral controllers found on the CPU itself. |
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133 | This class of code may be found in the following directory: |
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134 | |
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135 | @example |
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136 | c/src/lib/libcpu/@i{CPU} |
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137 | @end example |
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138 | |
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139 | CPU model dependent support code is found in the following directory: |
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140 | |
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141 | @example |
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142 | c/src/lib/libcpu/@i{CPU}/@i{CPU_MODEL} |
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143 | @end example |
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144 | |
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145 | @section Board Support Package Structure |
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146 | |
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147 | The BSPs are all under the c/src/lib/libbsp directory. Below this |
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148 | directory, there is a subdirectory for each CPU family. Each BSP |
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149 | is found under the subdirectory for the appropriate processor |
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150 | family (m68k, powerpc, etc.). In addition, there is source code |
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151 | available which may be shared across all BSPs regardless of |
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152 | the CPU family or just across BSPs within a single CPU family. This |
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153 | results in a BSP using the following directories: |
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154 | |
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155 | @example |
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156 | c/src/lib/libbsp/shared |
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157 | c/src/lib/libbsp/@i{CPU}/shared |
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158 | c/src/lib/libbsp/@i{CPU}/@i{BSP} |
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159 | @end example |
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160 | |
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161 | Under each BSP specific directory, there is a collection of |
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162 | subdirectories. For commonly provided functionality, the BSPs |
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163 | follow a convention on subdirectory naming. The following list |
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164 | describes the commonly found subdirectories under each BSP. |
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165 | |
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166 | @itemize @bullet |
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167 | |
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168 | @item @b{console}: |
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169 | is technically the serial driver for the BSP rather |
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170 | than just a console driver, it deals with the board |
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171 | UARTs (i.e. serial devices). |
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172 | |
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173 | @item @b{clock}: |
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174 | support for the clock tick -- a regular time basis to the kernel. |
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175 | |
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176 | @item @b{timer}: |
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177 | support of timer devices. |
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178 | |
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179 | @item @b{rtc}: |
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180 | support for the hardware real-time clock. |
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181 | |
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182 | @item @b{nvmem}: |
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183 | support for non-volatile memory such as EEPROM or Flash. |
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184 | |
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185 | @item @b{network}: |
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186 | the Ethernet driver. |
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187 | |
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188 | @item @b{shmsupp}: |
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189 | support of shared memory driver MPCI layer in a multiprocessor system, |
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190 | |
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191 | @item @b{include}: |
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192 | include files for this BSP. |
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193 | |
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194 | @item @b{wrapup}: |
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195 | bundles all the components necessary to construct the BSP library. |
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196 | |
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197 | @end itemize |
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198 | |
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199 | The build order of the BSP is determined by the Makefile structure. |
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200 | This structure is discussed in more detail in the @ref{Makefiles} |
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201 | chapter. |
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202 | |
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203 | @b{NOTE:} This manual refers to the gen68340 BSP for numerous concrete |
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204 | examples. You should have a copy of the gen68340 BSP available while |
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205 | reading this piece of documentation. This BSP is located in the |
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206 | following directory: |
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207 | |
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208 | @example |
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209 | c/src/lib/libbsp/m68k/gen68340 |
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210 | @end example |
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211 | |
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212 | Later in this document, the $BSP340_ROOT label will be used |
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213 | to refer to this directory. |
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214 | |
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