1 | RTEMS BSD USB and TCP/IP Developers Guide |
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2 | ========================================= |
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3 | Joel Sherrill <joel.sherrill@oarcorp.com> |
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4 | :Author Initials: JRS |
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5 | :toc: |
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6 | :icons: |
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7 | :numbered: |
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8 | :website: http://www.rtems.org/ |
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9 | |
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10 | RTEMS uses FreeBSD as the source of its TCP/IP and USB stacks. |
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11 | This is a developers guide which captures information on the |
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12 | process of merging code from FreeBSD, building this library, |
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13 | RTEMS specific support files, and general guidelines on what |
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14 | modifications to the FreeBSD source are permitted. |
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15 | |
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16 | Goals of this effort are: |
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17 | |
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18 | * Update TCP/IP and provide USB in RTEMS |
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19 | * Ease updating to future FreeBSD versions |
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20 | * Ease tracking changes in FreeBSD code |
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21 | * Minimize manual changes in FreeBSD code |
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22 | * Define stable kernel/device driver API which is implemented |
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23 | by both RTEMS and FreeBSD. This is the foundation of the port. |
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24 | |
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25 | We will work to push our changes upstream to the FreeBSD Project |
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26 | and minimize changes required at each update point. |
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27 | |
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28 | ************************************************************** |
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29 | This is a work in progress and is very likely to be incomplete. |
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30 | Please help by adding to it. |
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31 | ************************************************************** |
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32 | |
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33 | == Source Code Version Information |
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34 | |
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35 | * FreeBSD 8.2 SVN r222496 |
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36 | * RTEMS 4.11 |
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37 | - BSP must have support for all new BSD sys sections |
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38 | - It is preferable if the BSP uses linkcmds.base. |
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39 | - BSP must be from an architecture with Programmable Interrupt Controller |
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40 | interrupt model. |
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41 | |
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42 | The FreeBSD 8.2 SVN checkout will generally be referred to as the |
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43 | FreeBSD source in this document. An archive of the FreeBSD 8.2 SVN |
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44 | archive used is located at |
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45 | http://www.rtems.org/ftp/pub/rtems/people/joel/freebsd/ |
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46 | The SVN checkout command is this |
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47 | svn co http://svn.freebsd.org/base/releng/8.2/sys/ -r222496 freebsd-8.2 |
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48 | |
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49 | == Issues and To Do |
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50 | * Sebastian Huber: mentioned some simple test code which would verify |
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51 | that the BSD code/and or USB stack was initialized. This has been |
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52 | sent to Joel Sherrill and is pending merger. |
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53 | |
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54 | * Sebastian Huber and Joel Sherrill discussed the need for a a basic USB |
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55 | functionality test that is known to work on qemu pc. |
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56 | |
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57 | * Adapt generic IRQ PIC interface code to Simple Vectored Interrupt Model |
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58 | so that those architectures can use new TCP/IP and USB code. |
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59 | |
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60 | * in_cksum implementations for architectures not supported by FreeBSD. |
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61 | This will require figuring out where to put implementations that do |
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62 | not originate from FreeBSD and are populated via the script. |
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63 | |
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64 | * FreeBSD generic in_cksum implementation is missing in_cksum_split so |
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65 | currently cannot be used. |
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66 | |
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67 | * How does one initialize the TCP/IP stack? |
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68 | |
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69 | * linker section issues: I have undefined symbols for |
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70 | `_bsd__start_set_sysinit_set` and `_bsd__stop_set_sysinit_set`. |
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71 | Is this the only type of new section magic? What about the old sysctl_set? |
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72 | I added this to my linkcmds. |
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73 | |
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74 | [listing] |
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75 | ---- |
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76 | /* sysinit section? */ |
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77 | . = ALIGN (16); |
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78 | _bsd__start_set_sysinit_set = .; |
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79 | *(set_sys_init_*); |
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80 | _bsd__stop_set_sysinit_set = .; |
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81 | |
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82 | ---- |
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83 | |
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84 | * Why is the interrupt server used? The BSD interrupt handlers can block on |
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85 | synchronization primitives like mutexes. This is in contrast to RTEMS |
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86 | interrupt service routines. The BSPs using the generic interrupt support must |
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87 | implement the `bsp_interrupt_vector_enable()` and |
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88 | `bsp_interrupt_vector_disable()` routines. They normally enable/disable a |
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89 | particular interrupt source at the interrupt controller. This can be used to |
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90 | implement the interrupt server. The interrupt server is a task that wakes-up |
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91 | in case an associated interrupt happens. The interrupt source is disabled in |
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92 | a generic interrupt handler that wakes-up the interrupt server task. Once the |
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93 | postponed interrupt processing is performed in the interrupt server the |
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94 | interrupt source is enabled again. |
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95 | |
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96 | * Convert all BSP linkcmds to use a linkcmds.base so the sections are |
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97 | easier to insert. |
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98 | |
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99 | * rtems-bsd-init-with-irq.c: |
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100 | rtems_bsd_initialize_with_interrupt_server() has reference to |
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101 | rtems_interrupt_server_initialize() and this method is unimplemented |
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102 | - XXX BSP implements pieces |
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103 | - BSPs using this software stack must support it apparently. |
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104 | - What about Simple Vectored architectures? |
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105 | |
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106 | * maxproc variable referenced by rtems-bsd-resource.c. What should it |
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107 | be set to? |
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108 | |
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109 | * ngroups_max variable referenced by rtems-bsd-prot.c. - What should |
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110 | it be set to? |
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111 | |
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112 | * NIC Device Drivers |
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113 | - Only common NIC drivers have been included in the initial set. These do not |
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114 | include any system on chip or ISA drivers. |
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115 | - The ISA drivers require more BSD infrastructure to be addressed. This was |
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116 | outside the scope of the initial porting effort. |
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117 | |
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118 | == FreeBSD Source |
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119 | |
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120 | You should be able to rely on FreebSD manual pages and documentation |
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121 | for details on the code itself. |
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122 | |
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123 | === Automatically Generated FreeBSD Files |
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124 | |
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125 | The FreeBSD source tarball includes a file named Makefile.rtems which |
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126 | has stanzas to automatically generate some files using awk. For details |
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127 | on this, see http://www.freebsd.org/cgi/man.cgi?query=kobj&apropos=0&sektion=0&manpath=FreeBSD+9.0-RELEASE&arch=default&format=html |
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128 | |
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129 | XXX This needs more detail. |
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130 | |
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131 | === Rules for Modifying FreeBSD Source |
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132 | |
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133 | * Only add lines. Subtract code by added "ifndef __rtems__". This makes |
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134 | merging easier in the future. |
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135 | |
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136 | == libbsd Source |
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137 | |
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138 | === What is in git |
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139 | |
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140 | The git source is a self-contained kit with FreeBSD and RTEMS components |
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141 | pre-merged. The Makefile in this kit is automatically generated. |
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142 | |
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143 | Any changes to sources in the freebsd or contrib directories will need to |
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144 | be merged upstream into our master FreeBSD svn checkout. |
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145 | |
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146 | The FreeBSD sources managed in RTEMS libbsd git repository (e.g. contrib |
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147 | and freebsd directories) contain the "managed" version of the |
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148 | FreeBSD source. The FreeBSD SVN source is the "master" version. The |
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149 | freebsd-to-rtems.py script is used to transfer files between the two |
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150 | trees. In general terms, if you have modified FreeBSD in the RTEMS libbsd |
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151 | tree, you want to run the script in "revert" or "reverse" mode to move |
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152 | the source back so you can run an "svn diff" against the upstream FreeBSD |
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153 | source. If you want to transfer source from the FreeBSD SVN checkout to |
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154 | the RTEMS libbsd tree, then you want to run the script in "forward" or |
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155 | default mode. |
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156 | |
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157 | === Building RTEMS libbsd source |
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158 | |
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159 | You need to configure RTEMS for the desired BSP and install it. The |
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160 | following is the script used to build the powerpc/psim BSP for our |
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161 | internal testing purposes: |
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162 | |
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163 | [listing] |
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164 | ---- |
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165 | #! /bin/sh |
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166 | |
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167 | cd ${HOME}/newbsd |
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168 | rm -rf b-psim |
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169 | mkdir b-psim |
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170 | cd b-psim |
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171 | ../git/rtems/configure --target=powerpc-rtems4.11 \ |
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172 | --enable-rtemsbsp=psim --disable-networking \ |
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173 | --enable-tests=samples \ |
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174 | --prefix=${HOME}/newbsd/bsp-install >c.log 2>&1 && \ |
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175 | make >b.log 2>&1 && \ |
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176 | make install >i.log 2>&1 |
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177 | echo $? |
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178 | ---- |
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179 | |
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180 | Then edit the file config.inc to set RTEMS_MAKEFILE_PATH appropriately |
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181 | to indicate the ${prefix}/${target}/${BSP}. Continuing on the above, |
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182 | the config.inc used to match the above is: |
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183 | |
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184 | [listing] |
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185 | ---- |
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186 | RTEMS_MAKEFILE_PATH = ${HOME}/newbsd/bsp-install/powerpc-rtems4.11/psim/ |
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187 | INSTALL_BASE = ${HOME}/newbsd/install |
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188 | ---- |
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189 | |
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190 | The above installs the RTEMS libbsd kit into a separate place from |
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191 | RTEMS and the BSP. The RTEMS libbsd tests are built against an installed |
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192 | image of the RTEMS libbsd. By keeping it in a separate installation point |
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193 | from RTEMS itself, this makes it easier to remove a libbsd installation |
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194 | and have a clean test point. |
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195 | |
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196 | [listing] |
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197 | ---- |
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198 | make |
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199 | make install |
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200 | make -C testsuite |
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201 | ---- |
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202 | |
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203 | At this point, we expect multiple linker errors. That is what we are |
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204 | currently working on. |
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205 | |
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206 | === Organization |
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207 | |
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208 | The top level directory contains a few directories and files. The following |
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209 | are important to understand: |
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210 | |
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211 | * freebsd-to-rtems.py - script to convert to and free FreeBSD and RTEMS trees |
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212 | * Makefile - automatically generated |
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213 | * contrib/ - from FreeBSD by script. |
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214 | * freebsd/ - from FreeBSD by script. |
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215 | * rtemsbsd/ - RTEMS specific implementations of FreeBSD kernel support routines. |
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216 | * testsuite/ - RTEMS specific tests |
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217 | * libbsd.txt - Documentation in Asciidoc |
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218 | |
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219 | == Moving Code Between FreeBSD SVN and RTEMS libbsd |
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220 | |
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221 | The script freebsd-to-rtems.py is used to copy code from FreeBSD to the |
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222 | RTEMS libbsd tree and to reverse this process. This script attempts to |
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223 | automate this process as much as possible and performs some transformations |
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224 | on the FreeBSD code. Its command line arguments are shown below: |
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225 | |
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226 | [listing] |
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227 | ---- |
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228 | freebsd-to-rtems.py [args] |
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229 | -?|-h|--help print this and exit |
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230 | -d|--dry-run run program but no modifications |
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231 | -D|--diff provide diff of files between trees |
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232 | -e|--early-exit evaluate arguments, print results, and exit |
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233 | -m|--makefile just generate Makefile |
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234 | -R|--reverse default FreeBSD -> RTEMS, reverse that |
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235 | -r|--rtems RTEMS directory |
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236 | -f|--freebsd FreeBSD directory |
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237 | -v|--verbose enable verbose output mode |
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238 | ---- |
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239 | |
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240 | In its default mode of operation, freebsd-to-rtems.py is used to copy code |
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241 | from FreeBSD to the RTEMS libbsd tree and perform transformations. In forward |
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242 | mode, the script may be requested to just generate the Makefile. |
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243 | |
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244 | In "reverse mode", this script undoes those transformations and copies |
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245 | the source code back to the FreeBSD SVN tree. This allows us to do |
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246 | 'svn diff', evaluate changes made by the RTEMS Project, and report changes |
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247 | back to FreeBSD upstream. |
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248 | |
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249 | In either mode, the script may be asked to perform a dry-run or be verbose. |
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250 | Also, in either mode, the script is also smart enough to avoid copying over |
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251 | files which have not changed. This means that the timestamps of files are |
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252 | not changed unless the contents change. The script will also report the |
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253 | number of files which changed. In verbose mode, the script will print |
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254 | the name of the files which are changed. |
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255 | |
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256 | The following is an example forward run with no changes. |
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257 | |
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258 | [listing] |
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259 | ---- |
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260 | $ ~/newbsd/git/libbsd-8.2/freebsd-to-rtems.py \ |
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261 | -r /home/joel/newbsd/git/libbsd-8.2 \ |
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262 | -f /home/joel/newbsd/libbsd/freebsd-8.2 -v |
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263 | Verbose: yes |
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264 | Dry Run: no |
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265 | Only Generate Makefile: no |
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266 | RTEMS Directory: /home/joel/newbsd/git/libbsd-8.2 |
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267 | FreeBSD Directory: /home/joel/newbsd/libbsd/freebsd-8.2 |
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268 | Direction: forward |
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269 | Generating into /home/joel/newbsd/git/libbsd-8.2 |
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270 | 0 files were changed. |
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271 | ---- |
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272 | |
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273 | The script may also be used to generate a diff in either forward or reverse |
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274 | direction. |
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275 | |
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276 | == Initialization of RTEMS libbsd |
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277 | |
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278 | The initialization of the RTEMS libbsd is based on the FreeBSD SYSINIT(9) |
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279 | infrastructure. The key to initializing a system is to ensure that the desired |
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280 | device drivers are explicitly pulled into the linked application. This plus |
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281 | linking against the libbsd library will pull in the necessary FreeBSD |
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282 | infrastructure. |
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283 | |
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284 | The FreeBSD kernel is not a library like the RTEMS kernel. It is a bunch of |
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285 | object files linked together. If we have a library, then creating the |
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286 | executable is simple. We begin with a start symbol and recursively resolve all |
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287 | references. With a bunch of object files linked together we need a different |
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288 | mechanism. Most object files don't know each other. Lets say we have a driver |
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289 | module. The rest of the system has no references to this driver module. The |
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290 | driver module needs a way to tell the rest of the system: Hey, kernel I am |
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291 | here, please use my services! |
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292 | |
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293 | This registration of independent components is performed by SYSINIT(9) and |
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294 | specializations: |
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295 | |
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296 | http://www.freebsd.org/cgi/man.cgi?query=SYSINIT |
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297 | |
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298 | The SYSINIT(9) uses some global data structures that are placed in a certain |
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299 | section. In the linker command file we need this: |
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300 | |
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301 | [listing] |
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302 | ---- |
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303 | .robsdsets : { |
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304 | _bsd__start_set_modmetadata_set = .; |
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305 | *(_bsd_set_modmetadata_set); |
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306 | _bsd__stop_set_modmetadata_set = .; |
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307 | _bsd__start_set_sysctl_set = .; |
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308 | *(_bsd_set_sysctl_set); |
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309 | _bsd__stop_set_sysctl_set = .; |
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310 | } > REGION_RODATA AT > REGION_RODATA_LOAD |
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311 | |
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312 | .rwbsdsets : { |
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313 | _bsd__start_set_sysinit_set = .; |
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314 | *(_bsd_set_sysinit_set); |
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315 | _bsd__stop_set_sysinit_set = .; |
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316 | } > REGION_DATA AT > REGION_DATA_LOAD |
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317 | ---- |
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318 | |
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319 | Here you can see, that these global data structures are collected into |
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320 | continuous memory areas. This memory area can be identified by start and stop |
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321 | symbols. This constructs a table of uniform items. |
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322 | |
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323 | The low level FreeBSD code calls at some time during the initialization the |
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324 | mi_startup() function (machine independent startup). This function will sort |
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325 | the SYSINIT(9) set and call handler functions which perform further |
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326 | initialization. The last step is the scheduler invocation. |
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327 | |
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328 | The SYSINIT(9) routines are run in mi_startup() which is called by |
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329 | rtems_bsd_initialize(). |
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330 | |
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331 | This is also explained in "The Design and Implementation of the FreeBSD |
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332 | Operating System" section 14.3 "Kernel Initialization". |
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333 | |
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334 | In RTEMS we have a library and not a bunch of object files. Thus we need a way |
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335 | to pull-in the desired services out of the libbsd. Here the |
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336 | "rtems-bsd-sysinit.h" comes into play. The SYSINIT(9) macros have been |
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337 | modified and extended for RTEMS in "sys/kernel.h": |
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338 | |
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339 | [listing] |
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340 | ---- |
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341 | #ifndef __rtems__ |
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342 | #define C_SYSINIT(uniquifier, subsystem, order, func, ident) \ |
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343 | static struct sysinit uniquifier ## _sys_init = { \ |
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344 | subsystem, \ |
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345 | order, \ |
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346 | func, \ |
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347 | (ident) \ |
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348 | }; \ |
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349 | DATA_SET(sysinit_set,uniquifier ## _sys_init) |
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350 | #else /* __rtems__ */ |
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351 | #define SYSINIT_ENTRY_NAME(uniquifier) \ |
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352 | _bsd_ ## uniquifier ## _sys_init |
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353 | #define SYSINIT_REFERENCE_NAME(uniquifier) \ |
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354 | _bsd_ ## uniquifier ## _sys_init_ref |
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355 | #define C_SYSINIT(uniquifier, subsystem, order, func, ident) \ |
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356 | struct sysinit SYSINIT_ENTRY_NAME(uniquifier) = { \ |
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357 | subsystem, \ |
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358 | order, \ |
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359 | func, \ |
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360 | (ident) \ |
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361 | }; \ |
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362 | DATA_SET(sysinit_set,SYSINIT_ENTRY_NAME(uniquifier)) |
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363 | #define SYSINIT_REFERENCE(uniquifier) \ |
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364 | extern struct sysinit SYSINIT_ENTRY_NAME(uniquifier); \ |
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365 | static struct sysinit const * const \ |
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366 | SYSINIT_REFERENCE_NAME(uniquifier) __used \ |
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367 | = &SYSINIT_ENTRY_NAME(uniquifier) |
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368 | #define SYSINIT_MODULE_REFERENCE(mod) \ |
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369 | SYSINIT_REFERENCE(mod ## module) |
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370 | #define SYSINIT_DRIVER_REFERENCE(driver, bus) \ |
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371 | SYSINIT_MODULE_REFERENCE(driver ## _ ## bus) |
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372 | #endif /* __rtems__ */ |
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373 | ---- |
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374 | |
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375 | Here you see that the SYSINIT(9) entries are no longer static. The |
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376 | *_REFERENCE() macros will create references to the corresponding modules which |
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377 | are later resolved by the linker. The application has to provide an object |
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378 | file with references to all required FreeBSD modules. |
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379 | |
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380 | The FreeBSD device model is quite elaborated (with follow-ups): |
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381 | |
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382 | http://www.freebsd.org/cgi/man.cgi?query=driver |
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383 | |
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384 | The devices form a tree with the Nexus device at a high-level. This Nexus |
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385 | device is architecture specific in FreeBSD. In RTEMS we have our own Nexus |
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386 | device, see "rtems-bsd-nexus.c". It uses a table to add child devices: |
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387 | |
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388 | [listing] |
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389 | ---- |
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390 | const char *const _bsd_nexus_devices [] = { |
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391 | #ifdef NEED_USB_OHCI |
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392 | "ohci", |
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393 | #endif |
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394 | #ifdef NEED_USB_EHCI |
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395 | "ehci", |
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396 | #endif |
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397 | #ifdef NEED_SDHC |
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398 | "sdhci", |
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399 | #endif |
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400 | NULL |
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401 | }; |
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402 | ---- |
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403 | |
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404 | This table must be provided by the application. |
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405 | |
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406 | === SYSCTL_NODE Example |
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407 | |
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408 | During development, we had an undefined reference to |
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409 | _bsd_sysctl__net_children that we had trouble tracking down. Thanks to |
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410 | Chris Johns, we located it. He explained how to read SYSCTL_NODE |
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411 | definitions. This line from freebsd/netinet/in_proto.c is attempting |
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412 | to add the "inet" node to the parent node "_net". |
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413 | |
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414 | [listing] |
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415 | ---- |
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416 | SYSCTL_NODE(_net, PF_INET, inet, CTLFLAG_RW, 0, |
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417 | "Internet Family"); |
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418 | ---- |
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419 | |
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420 | Our problem was that we could not find where _bsd_sysctl__net_children |
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421 | was defined. Chris suggested that when in doubt compile with -save-temps |
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422 | and look at the preprocessed .i files. But he did not need that. He |
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423 | explained that this the symbol name _bsd_sysctl__net_children was |
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424 | automatically generated by a SYSCTL_NODE as follows: |
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425 | |
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426 | * _bsd_ - added by RTEMS modifications to SYSCTL_NODE macro |
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427 | * sysctl_ - boilerplace added by SYSCTL_NODE macro |
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428 | * "" - empty string for parent node |
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429 | * net - name of SYSCTL_NODE |
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430 | * children - added by SYSCTL macros |
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431 | |
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432 | This was all generated by a support macro declaring the node as this: |
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433 | |
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434 | [listing] |
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435 | ---- |
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436 | struct sysctl_oid_list SYSCTL_NODE_CHILDREN(parent, name); |
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437 | ---- |
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438 | |
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439 | Given this information, we located this SYSCTL_NODE declaration in |
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440 | kern/kern_mib.c |
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441 | |
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442 | [listing] |
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443 | ---- |
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444 | SYSCTL_NODE(, CTL_KERN, kern, CTLFLAG_RW, 0, |
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445 | "High kernel, proc, limits &c"); |
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446 | ---- |
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447 | |
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448 | == Core FreeBSD APIs and RTEMS Replacements == |
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449 | |
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450 | === SX(9) (Shared/exclusive locks) === |
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451 | |
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452 | http://www.freebsd.org/cgi/man.cgi?query=sx |
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453 | |
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454 | Binary semaphores (this neglects the ability to allow shared access). |
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455 | |
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456 | === MUTEX(9) (Mutual exclusion) === |
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457 | |
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458 | http://www.freebsd.org/cgi/man.cgi?query=mutex |
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459 | |
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460 | Binary semaphores (not recursive mutexes are not supported this way). |
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461 | |
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462 | === RWLOCK(9) (Reader/writer lock) === |
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463 | |
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464 | http://www.freebsd.org/cgi/man.cgi?query=rwlock |
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465 | |
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466 | POSIX r/w lock. |
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467 | |
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468 | === RMLOCK(9) (Reader/writer lock optimized for mostly read access patterns) === |
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469 | |
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470 | http://www.freebsd.org/cgi/man.cgi?query=rmlock |
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471 | |
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472 | POSIX r/w lock. |
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473 | |
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474 | === CONDVAR(9) (Condition variables) === |
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475 | |
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476 | http://www.freebsd.org/cgi/man.cgi?query=condvar |
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477 | |
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478 | POSIX condition variables with modifications (hack). |
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479 | |
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480 | === CALLOUT(9) (Timer functions) === |
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481 | |
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482 | http://www.freebsd.org/cgi/man.cgi?query=callout |
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483 | |
---|
484 | Timer server. |
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485 | |
---|
486 | === TASKQUEUE(9) (Asynchronous task execution) === |
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487 | |
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488 | http://www.freebsd.org/cgi/man.cgi?query=taskqueue |
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489 | |
---|
490 | TBD. |
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491 | |
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492 | === KTHREAD(9), KPROC(9) (Tasks) === |
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493 | |
---|
494 | http://www.freebsd.org/cgi/man.cgi?query=kthread |
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495 | |
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496 | http://www.freebsd.org/cgi/man.cgi?query=kproc |
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497 | |
---|
498 | Tasks. |
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499 | |
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500 | === ZONE(9) (Zone allocator) === |
---|
501 | |
---|
502 | http://www.freebsd.org/cgi/man.cgi?query=zone |
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503 | |
---|
504 | TBD. |
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505 | |
---|
506 | === devfs (Device file system) === |
---|
507 | |
---|
508 | Dummy, IMFS or new implementation (currently dummy). |
---|
509 | |
---|
510 | === psignal (Signals) === |
---|
511 | |
---|
512 | TBD. Seems to be not needed. |
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513 | |
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514 | === poll, select === |
---|
515 | |
---|
516 | TBD. Seems to be not needed. |
---|
517 | |
---|
518 | === RMAN(9) (Resource management) === |
---|
519 | |
---|
520 | http://www.freebsd.org/cgi/man.cgi?query=rman |
---|
521 | |
---|
522 | TBD. Seems to be not needed. |
---|
523 | |
---|
524 | === DEVCLASS(9), DEVICE(9), DRIVER(9), MAKE_DEV(9) (Device management) === |
---|
525 | |
---|
526 | http://www.freebsd.org/cgi/man.cgi?query=devclass |
---|
527 | |
---|
528 | http://www.freebsd.org/cgi/man.cgi?query=device |
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529 | |
---|
530 | http://www.freebsd.org/cgi/man.cgi?query=driver |
---|
531 | |
---|
532 | http://www.freebsd.org/cgi/man.cgi?query=make_dev |
---|
533 | |
---|
534 | Use FreeBSD implementation as far as possible. FreeBSD has a nice API for |
---|
535 | dynamic device handling. It may be interesting for RTEMS to use this API |
---|
536 | internally in the future. |
---|
537 | |
---|
538 | === BUS_SPACE(9), BUS_DMA(9) (Bus and DMA access) === |
---|
539 | |
---|
540 | http://www.freebsd.org/cgi/man.cgi?query=bus_space |
---|
541 | |
---|
542 | http://www.freebsd.org/cgi/man.cgi?query=bus_dma |
---|
543 | |
---|
544 | Likely BSP dependent. A default implementation for memory mapped linear access |
---|
545 | is easy to provide. The current heap implementation supports all properties |
---|
546 | demanded by bus_dma (including the boundary constraint). |
---|