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5 5
6<title>Development Cases</title> 6<title>Development Cases</title>
7 7
8<section id='cases-intro'> 8<para>
9 <title>Introduction</title> 9For the purposes of this manual we are going to focus on two common development cases or groupings: System Development and User Application Development. System Development covers Board Support Package (BSP) development and kernel image modification. User Application Development covers development of applications that you intend to run on some target hardware.
10</para>
11
12<para>
13[WRITERS NOTE: What is undetermined at this point is how much of the entire development process we include in this particular chapter. In other words, do we cover debugging and emulation steps here on a case-specific basis? Or, do we capture that information in the appropriate subsequent chapter by case?]
14</para>
15
16<section id='system-development'>
17 <title>System Development</title>
18
10 <para> 19 <para>
11 The Yocto Project presents the kernel as a fully patched, history-clean Git 20System development involves modification or creation of an image that you want to run on a specific hardware target. Usually when you want to create an image that runs on embedded hardware the image does not require the same amount of features that a full-fledged Linux distribution provides. Thus, you can create a much smaller image that is designed to just use the hardware features for your particular hardware.
12 repository.
13 The Git tree represents the selected features, board support,
14 and configurations extensively tested by Yocto Project.
15 The Yocto Project kernel allows the end user to leverage community
16 best practices to seamlessly manage the development, build and debug cycles.
17 </para> 21 </para>
22
18 <para> 23 <para>
19 This manual describes the Yocto Project kernel by providing information 24To help you understand how system development works in the Yocto Project, this section covers two types of image development: BSP creation and kernel modification.
20 on its history, organization, benefits, and use.
21 The manual consists of two sections:
22 <itemizedlist>
23 <listitem><para>Concepts - Describes concepts behind the kernel.
24 You will understand how the kernel is organized and why it is organized in
25 the way it is. You will understand the benefits of the kernel's organization
26 and the mechanisms used to work with the kernel and how to apply it in your
27 design process.</para></listitem>
28 <listitem><para>Using the Kernel - Describes best practices and "how-to" information
29 that lets you put the kernel to practical use. Some examples are "How to Build a
30 Project Specific Tree", "How to Examine Changes in a Branch", and "Saving Kernel
31 Modifications."</para></listitem>
32 </itemizedlist>
33 </para> 25 </para>
34 <para> 26
35 For more information on the kernel, see the following links: 27 <section id='developing-a-board-support-package-bsp'>
36 <itemizedlist> 28 <title>Developing a Board Support Package (BSP)</title>
37 <listitem><para><ulink url='http://ldn.linuxfoundation.org/book/1-a-guide-kernel-development-process'></ulink></para></listitem> 29
38 <listitem><para><ulink url='http://userweb.kernel.org/~akpm/stuff/tpp.txt'></ulink></para></listitem> 30 <para>
39 <listitem><para><ulink url='http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob_plain;f=Documentation/HOWTO;hb=HEAD'></ulink></para></listitem> 31A BSP is a package of recipes that when applied while building an image results in an image you can run on a particular board. Thus, the package, when compiled into the new image, supports the operation of the board.
40 </itemizedlist>
41 <para>
42 You can find more information on Yocto Project by visiting the website at
43 <ulink url='http://www.yoctoproject.org'></ulink>.
44 </para> 32 </para>
45 </para>
46</section>
47 33
34 <para>
35Packages consist of recipes. Recipes are sets of instructions for building a package. The recipes describe where to get source code and what patches to apply. Recipes also describe dependencies for libraries or for other recipes. They also contain configuration and compilation options. Recipes are logical units of execution.
36 </para>
37
38 <para>
39Here are the basic steps involved in creating a BSP:
40 <orderedlist>
41 <listitem><para>1.Be sure you are set up to use Yocto Project (see Chapter 2)</para></listitem>
42 <listitem><para>1.Choose a BSP available with Yocto Project that most closely represents your hardware</para></listitem>
43 <listitem><para>1.Get set up with a base BSP</para></listitem>
44 <listitem><para>1.Make a copy of the existing BSP and isolate your work by creating a layer for your recipes</para></listitem>
45 <listitem><para>1.Make configuration and recipe changes to your new BSP layer</para></listitem>
46 <listitem><para>1.Prepare for the build</para></listitem>
47 <listitem><para>1.Select and configure the kernel (NOTE: Not sure on this step)</para></listitem>
48 <listitem><para>1.Identify the machine branch in the Git repository</para></listitem>
49 <listitem><para>1.Build the image</para></listitem>
50 </orderedlist>
51You can view a video presentation of the BSP creation process at http://free-electorons.com/blog/elc-2011-videos. You can also find supplemental information in the BSP Manual at http://yoctoproject.org//docs/1.1/bsp-guide/bsp-guide.html. Finally, there is another write up of the example used in this section at https://wiki.yoctoproject.org/wiki/Transcript:_creating_one_generic_Atom_BSP_from_another you might find helpful.
52 </para>
53
54 <section id='setting-up-yocto-project'>
55 <title>Setting Up Yocto Project</title>
56
57 <para>
58For general host development system preparation such as package requirements and operating system requirements, see Chapter 2 of this manual or the Yocto Project Quick start at http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html.
59 </para>
60
61 <para>
62You need to have the Yocto Project source tree available on your host system. You can get that through tarball extraction or by initializing and checking out the Yocto Project Git repository. Typically, checking out the Git repository is the method to use. This allows you to maintain a complete history of changes and facilitates you contributing back to the Yocto Project. However, if you just want the source you can download the Yocto Project Release tarball from http://yoctoproject.org/download. If you download the tarball you can extract it into any directory you want using the tar command. For example, the following commands extract the 1.0.1 release tarball into /usr/local/yocto with the Yocto Project source directory as poky.bernard.5.0.1.tar.bz2:
63 <literallayout class='monospaced'>
64 /usr/local/yocto$ tar xfj poky.bernard.5.0.1.tar.bz2
65 </literallayout>
66 </para>
67
68 <para>
69The following transcript shows how to initialize a Git repository and checkout the Yocto Project source tree:
70 <literallayout class='monospaced'>
71 /usr/local/yocto$ git init
72 Initialized empty Git repository in /usr/local/yocto/.git
73 /usr/local/yocto$ git remote add poky git://git.yoctoproject.org/poky.git
74 /usr/local/yocto$ git remote update
75 Fetching poky
76 remote: Counting objects: 106111, done.
77 remote: Compressing objects: 100% (36106/36106), done.
78 remote: Total 106111 (delta 72275), reused 99193 (delta 66808)
79 Receiving objects: 100% (106111/106111), 69.51 MiB | 518 KiB/s, done.
80 Resolving deltas: 100% (72275/72275), done.
81 From git://git.yoctoproject.org/poky
82 * [new branch] 1.1_M1 -> poky/1.1_M1
83 * [new branch] 1.1_M2 -> poky/1.1_M2
84 * [new branch] bernard -> poky/bernard
85 * [new branch] blinky -> poky/blinky
86 * [new branch] clyde -> poky/clyde
87 * [new branch] elroy -> poky/elroy
88 * [new branch] green -> poky/green
89 * [new branch] laverne -> poky/laverne
90 * [new branch] master -> poky/master
91 * [new branch] pinky -> poky/pinky
92 * [new branch] purple -> poky/purple
93 * [new tag] 1.1_M1.final -> 1.1_M1.final
94 * [new tag] 1.1_M2.rc1 -> 1.1_M2.rc1
95 * [new tag] bernard-5.0.1 -> bernard-5.0.1
96 * [new tag] pinky-3.1.2 -> pinky-3.1.2
97 From git://git.yoctoproject.org/poky
98 * [new tag] 1.1_M1.rc1 -> 1.1_M1.rc1
99 * [new tag] 1.1_M1.rc2 -> 1.1_M1.rc2
100 * [new tag] bernard-1.0rc1 -> bernard-1.0rc1
101 * [new tag] bernard-5.0 -> bernard-5.0
102 * [new tag] bernard-5.0-alpha -> bernard-5.0-alpha
103 * [new tag] bernard-5.0rc1 -> bernard-5.0rc1
104 * [new tag] bernard-5.0rc2 -> bernard-5.0rc2
105 * [new tag] laverne-4.0 -> laverne-4.0
106 * [new tag] laverne-4.0.1 -> laverne-4.0.1
107 * [new tag] m4 -> m4
108 * [new tag] purple-3.2 -> purple-3.2
109 * [new tag] purple-3.2.1 -> purple-3.2.1
110 </literallayout>
111 </para>
112
113 <para>
114Once you have the repository set up, you have many development branches from which you can work. For this example we are going to use the Yocto Project 1.0.1 Release, which maps to the Bernard 5.0.1 tag in Git.
115 <literallayout class='monospaced'>
116 /usr/local/yocto$ git checkout -b Bernard-5.0.1 bernard-5.0.1
117 Switched to a new branch 'bernard-5.0.1'
118 </literallayout>
119 </para>
120 </section>
121
122 <section id='choosing-a-base-bsp'>
123 <title>Choosing a Base BSP</title>
124
125 <para>
126The Yocto Project ships with several BSPs that support various hardware. It is best to base your new BSP on an existing BSP rather than create all the recipes and configuration files from scratch. While it is possible to create everything from scratch, basing your new BSP on something that is close is much easier. Or, at a minimum, it gives you some structure with which to start.
127 </para>
128
129 <para>
130At this point you need to understand your target hardware well enough to determine which existing BSP most closely matches it. Things to consider are your hardware’s on-board features such as CPU type and graphics support. You should look at the README files for supported BSPs to get an idea of which one you could use. A generic Atom-based BSP to consider is the Crown Bay with no Intel® Embedded Media Graphics Driver (EMGD) support. That is the BSP that this example is going to use.
131 </para>
132
133 <para>
134To see the supported BSPs go to http://www.yoctoproject.org/download and click on “BSP Downloads.”
135 </para>
136 </section>
137
138 <section id='getting-your-base-bsp'>
139 <title>Getting Your Base BSP</title>
140
141 <para>
142You need to have the base BSP layer on your development system. Like the Yocto Project source tree you can get the BSP layer one of two ways: download the tarball and extract it, or initialize a Git repository and check out the BSP. You should use the same method that you used for the Yocto Project source tree.
143 </para>
144
145 <para>
146If you are using tarball extraction then simply download the tarball for the base BSP you chose in the previous step and then extract it into any directory you choose using the tar command. Upon extraction, the BSP source directory (layer) will be named <filename>meta-&lt;BSP_name&gt;</filename>. The following command extracts the Crown Bay BSP into a directory named meta-crownbay:
147 <literallayout class='monospaced'>
148 /usr/local$ tar xjf crownbay-noemgd-bernard-5.0.1.tar.bz2
149 </literallayout>
150 </para>
151
152 <para>
153If you initialized a Yocto Project Git repository then you need to do the same for the BSP, which is located in the meta-intel Git repository. The meta-intel repository contains all the metadata that supports BSP creation.
154 </para>
155
156 <para>
157The following transcript shows the steps to create and set up the meta-intel Git repository inside the Yocto Project Git repository:
158 <literallayout class='monospaced'>
159 /usr/local/yocto$ mkdir meta-intel
160 /usr/local/yocto$ cd meta-intel
161 /usr/local/yocto/meta-intel$ git init
162 Initialized empty Git repository in /usr/local/yocto/meta-intel/.git/
163 /usr/local/yocto/meta-intel$ git remote add meta-intel \ git://git.yoctoproject.org/meta-intel.git
164 /usr/local/yocto/meta-intel$ git remote update
165 Fetching meta-intel
166 remote: Counting objects: 1240, done.
167 remote: Compressing objects: 100% (1008/1008), done.
168 remote: Total 1240 (delta 513), reused 85 (delta 27)
169 Receiving objects: 100% (1240/1240), 1.55 MiB | 510 KiB/s, done.
170 Resolving deltas: 100% (513/513), done.
171 From git://git.yoctoproject.org/meta-intel
172 * [new branch] 1.1_M1 -> meta-intel/1.1_M1
173 * [new branch] 1.1_M2 -> meta-intel/1.1_M2
174 * [new branch] bernard -> meta-intel/bernard
175 * [new branch] dvhart/n450 -> meta-intel/dvhart/n450
176 * [new branch] laverne -> meta-intel/laverne
177 * [new branch] master -> meta-intel/master
178 </literallayout>
179 </para>
180
181 <para>
182Once you have the repository set up, you have many development branches from which you can work. For this example we are going to use Bernard 5.0.
183 <literallayout class='monospaced'>
184 /usr/local/yocto/meta-intel$ git checkout -b Bernard-5.0.1 meta-intel/bernard
185 Branch Bernard-5.0.1 set up to track remote branch bernard from meta-intel.
186 Switched to a new branch 'bernard-5.0.1'
187 </literallayout>
188 </para>
189 </section>
190
191 <section id='making-a-copy-of-the-base bsp-to-create-your-new-bsp-layer'>
192 <title>Making a Copy of the Base BSP to Create Your New BSP Layer</title>
193
194 <para>
195Now that you have the Yocto Project and base BSP source you need to create a new layer for your BSP.
196 </para>
197
198 <para>
199Layers are ideal for isolating and storing work for a given piece of hardware. A layer is really just a location or area in which you place the recipes for your BSP. In fact, a BSP is, in itself, a special type of layer. Consider an application as another example that illustrates a layer. Suppose you are creating an application that has library or other dependencies in order for it to compile and run. The layer, in this case, would be where all the recipes that define those dependencies are kept. The key point for a layer is that it is an isolated area that contains all the relevant information for the project that the Yocto Project build system knows about.
200 </para>
201
202 <para>
203[WRITER'S NOTE: The Yocto Project supports four BSPs that are part of the Yocto Project release: atom-pc, beagleboard, mpc8315e, and routerstationpro. The recipes and configurations for these four BSPs are located and dispersed within meta, which can be found in the Yocto Project source directory. Consequently, they are not totally isolated in the spirit of layers unless you think of meta as a layer itself. On the other hand, the Yocto Project has isolated BSP layers within meta-intel for the Crown Bay, Emenlow, Jasper Forest, N450, and Sugar Bay. [NOTE: meta-yocto, meta, and meta-intel need some explanation. Not sure about the relationship of meta-yocto as compared to meta-intel.]
204 </para>
205
206 <para>
207When you set up a layer for a new BSP you should follow a standard layout. This layout is described in the BSP Manual at http://www.yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html#bsp-filelayout. In the standard layout you will notice a suggested hierarchy for BSP kernel recipes, graphics recipes, and configuration information. You can see the standard layout for the Crown Bay BSP in this example by examining the directory structure of meta-crownbay.
208 </para>
209
210 <para>
211To create your BSP layer you simply copy the meta-crownbay layer to a new layer. For this example the new layer is named meta-mymachine. The name must follow the BSP layer naming convention, which is <filename>meta-&lt;name&gt;</filename>. The following example assumes a meta-intel Git repository. If you downloaded and expanded a Crown Bay tarball then you simply copy the resulting meta-crownbay directory structure to a location of your choice:
212 <literallayout class='monospaced'>
213 /usr/local/yocto/meta-intel$ cp -a meta-crownbay/ meta-mymachine
214 </literallayout>
215 </para>
216 </section>
217
218 <section id='making-changes-to-your-bsp'>
219 <title>Making Changes to Your BSP</title>
220
221 <para>
222Right now you have two identical BSP layers with different names: meta-crownbay and meta-mymachine. You need to change your configurations so that they work for your new BSP and your particular hardware. We will look first at the configurations, which are all done in the layer’s conf directory.
223 </para>
224
225 <para>
226First, since in this example the new BSP will not support EMGD we will get rid of the crownbay.conf file and then rename the crownbay-noemgd.conf file to mymachine.conf. Much of what we do in the configuration directory is designed to help the Yocto Project build system work with the new layer and to be able to find and use the right software. The following two commands result in a single machine configuration file named mymachine.conf.
227 <literallayout class='monospaced'>
228 /usr/local/yocto/meta-intel$ rm meta-mymachine/conf/machine/crownbay.conf
229 /usr/local/yocto/meta-intel$ mv meta-mymachine/conf/machine/crownbay-noemgd.conf \
230 meta-mymachine/conf/machine/mymachine.conf
231 </literallayout>
232 </para>
48 233
234 <para>
235The next step makes changes to mymachine.conf itself. The only changes needed for this example are changes to the comment lines and to the Source Revision (SRCREV) lines at the bottom of the file.
236 </para>
49 237
238 <para>
239For the comments the string crownbay-noemgd needs to be changed to mymachine.
240 </para>
50 241
242 <para>
243To understand how to complete the changes to the SRCREV statements we need to know which kernel we are using. The PREFERRED_PROVIDER_virtual/kernel statement in the file specifies the kernel we are going to use. We are going to use linux-yocto-stable. The SRCREV statement pairs point to the exact machine branch (commit) and meta branch in the Git repository. Right now the SRCREV variables are as follows in mymachine.conf:
244 <literallayout class='monospaced'>
245 SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= \ "56fe215d3f1a2cc3a5a26482ac9809ba44495695"
246 SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= \ "e1f85a470934a0cf6abde5d95533e74501822c6b"
51 247
248 SRCREV_machine_pn-linux-yocto-stable_crownbay-noemgd ?= \ "56fe215d3f1a2cc3a5a26482ac9809ba44495695"
249 SRCREV_meta_pn-linux-yocto-stable_crownbay-noemgd ?= \ "e1f85a470934a0cf6abde5d95533e74501822c6b"
250 </literallayout>
251 </para>
52 252
253 <para>
254You will notice that there are two pairs of SRCREV statements. The first pair points to a current development kernel, which we don’t care about in this example. The bottom pair points to the stable kernel that we will use: linux-yocto-stable. At this point though, the unique commit strings all are still associated with Crown Bay. So the next changes we make to the configuration file gets rid of the pair that points to the development kernel and provides new commit strings that points to the atom-pc-standard, which we are choosing for the initial build of this BSP. Here are the final SRCREV statements:
255 <literallayout class='monospaced'>
256 SRCREV_machine_pn-linux-yocto-stable_mymachine ?= \ "72ca49ab08b8eb475cec82a10049503602325791"
257 SRCREV_meta_pn-linux-yocto-stable_mymachine ?= \ "ec26387cb168e9e0976999b528b5a9dd62e3157a"
258 </literallayout>
259 </para>
53 260
261 <para>
262If you are familiar with Git repositories you probably won’t have trouble locating the exact commit strings you need to change the SRCREV statements. You can find all the machine and meta branch points (commits) for the linux-yocto-2.6.34 kernel at link http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-2.6.34.
263 </para>
264
265 <para>
266If you need a little more assistance after going to the link then do the following:
267 <orderedlist>
268 <listitem><para>1.Go to the http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-2.6.34 link</para></listitem>
269 <listitem><para>1.Expand the list of branches by clicking […]</para></listitem>
270 <listitem><para>1.Click on the atom-pc-standard branch</para></listitem>
271 <listitem><para>1.Click on the commit column header to view the top commit</para></listitem>
272 <listitem><para>1.Copy the commit string for use in the mymachine.conf file</para></listitem>
273 </orderedlist>
274 </para>
275
276 <para>
277For the SRCREV statement that points to the meta branch use the same procedure except expand the wrs_meta branch in step 2 above.
278 </para>
279
280 <para>
281The next configuration file in the new BSP layer we need to edit is layer.conf. This file identifies build information needed for the new layer. You can see http://www.yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html#bsp-filelayout-layer for more information on this configuration file. Basically, we are removing statements that support EMGD and changing the ones that support no EMGD.
282 </para>
283
284 <para>
285First, remove these statements from the file:
286 <literallayout class='monospaced'>
287 BBFILE_COLLECTIONS_crownbayd += "crownbay"
288 BBFILE_PATTERN_crownbay := "^${LAYERDIR}/"
289 BBFILE_PRIORITY_crownbay = "6"
290 </literallayout>
291 </para>
292
293 <para>
294This leaves three similar statements that we care about:
295 <literallayout class='monospaced'>
296 BBFILE_COLLECTIONS_crownbay-noemgd += "crownbay-noemgd"
297 BBFILE_PATTERN_crownbay-noemgd := "^${LAYERDIR}/"
298 BBFILE_PRIORITY_crownbay-noemgd = "6"
299 </literallayout>
300 </para>
301
302 <para>
303Simply substitute the machine string name crownbay-noemgd with the new machine name mymachine to get the following:
304 <literallayout class='monospaced'>
305 BBFILE_COLLECTIONS_mymachine += "mymachine"
306 BBFILE_PATTERN_mymachine := "^${LAYERDIR}/"
307 BBFILE_PRIORITY_mymachine = "6"
308 </literallayout>
309 </para>
310
311 <para>
312Now we will take a look at the recipes in your new layer. The standard BSP structure has areas for BSP, graphics, and kernel recipes. When you create a BSP you use these areas for appropriate recipes and append files. Recipes take the form of .bb files. If you want to leverage off of existing recipes elsewhere in the Yocto Project source tree but change them you can use .bbappend files. All new recipes and append files for your layer go in the layer’s recipes-bsp, recipes-kernel, and recipes-graphics directories.
313 </para>
314
315 <para>
316For this example we are not adding any new BSP recipes. And, we only need to remove the formfactor we do not want and change the name of the remaining one that supports no EMGD. These commands take care of the new layer’s BSP recipes:
317 <literallayout class='monospaced'>
318 /usr/local/yocto/meta-intel$ rm -rf \
319 meta-mymachine/recipes-bsp/formfactor/formfactor/crownbay
320 /usr/local/yocto/meta-intel$ mv \
321 meta-mymachine/recipes-bsp/formfactor/formfactor/crownbay-noemgd/ \
322 meta-mymachine/recipes-bsp/formfactor/formfactor/mymachine
323 </literallayout>
324 </para>
325
326 <para>
327For this example we want to remove anything that supports EMGD. The following command cleans up the recipes-graphics directory:
328 <literallayout class='monospaced'>
329 /usr/local/yocto/meta-intel$ rm –rf \
330 meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-emgd*
331 </literallayout>
332 </para>
333
334 <para>
335At this point the recipes-graphics directory just has files that support Video Electronics Standards Association (VESA) graphics modes. However, we still need to rename a directory in the layer. This command applies the final change to the recipes-graphics directory:
336 <literallayout class='monospaced'>
337 /usr/local/yocto/meta-intel$ mv \
338 meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd \
339 meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-config/mymachine
340 </literallayout>
341 </para>
342
343 <para>
344Finally, let us look at the recipes-kernel directory in the example. The only file we are concerned with for the example is linux-yocto-stable_git.bbappend. The other files all support the EMGD feature of Crown Bay. These commands clean up the directory:
345 <literallayout class='monospaced'>
346 /usr/local/yocto/meta-intel$ rm –rf meta-mymachine/recipes-kernel/linux/linux-yocto
347 /usr/local/yocto/meta-intel$ rm –rf \
348 meta-mymachine/recipes-kernel/linux/linux-yocto-stable
349 /usr/local/yocto/meta-intel$ rm \
350 meta-mymachine/recipes-kernel/linux/linux-yocto_git.bbappend
351 </literallayout>
352 </para>
353
354 <para>
355The linux-yocto-stable_git.bbappend file appends a Yocto Project recipe having the same name. The changes we need to make are to remove the statements that support EMGD and change the remaining Crown Bay strings to be mymachine. We also do not need to include the pointer to the EMGD licenses patch at the end of the file. Here is the original file:
356 <literallayout class='monospaced'>
357 FILESEXTRAPATHS := “${THISDIR}/${PN}”
358 COMPATIBLE_MACHINE_crownbay = “crownbay”
359 KMACHINE_CROWNBAY = “CROWNBAY”
360 COMPATIBLE_MACHINE_crownbay-noemgd = “crownbay-noemgd”
361 KMACHINE_crownbay-noemgd = “crownbay”
362 SRC_URI += file://0001-crownbay-update-a-handful-of-EMGD-licenses.patch
363 </literallayout>
364 </para>
365
366 <para>
367After editing the file it looks like this:
368 <literallayout class='monospaced'>
369 FILESEXTRAPATHS := “${THISDIR}/${PN}”
370 COMPATIBLE_MACHINE_mymachine = “mymachine”
371 KMACHINE_mymachine = “mymachine
372 </literallayout>
373 </para>
374
375 <para>
376In summary, the edits to the layer’s recipe files result in removal of any files and statements that do not support your targeted hardware in addition to the inclusion of any new recipes you might need. In this example, it was simply a matter of ridding the new layer meta-machine of any code that supported the EMGD features. We did not introduce any new recipes to the layer.
377 </para>
378
379 <para>
380Finally, it is also important to update the layer’s README file so that the information in it reflects your BSP.
381 </para>
382 </section>
383
384 <section id='preparing-for-the-build'>
385 <title>Preparing for the Build</title>
386
387 <para>
388Once you have made all the changes to your BSP layer there remains a few things you need to do for the Yocto Project build system in order for it to create your image. You need to get the build environment ready by sourcing an environment setup script and you need to be sure two key configuration files are configured appropriately.
389 </para>
390
391 <para>
392The entire process for building an image is overviewed in the Yocto Project Quick Start at http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#building-image. You might want to reference this information. The remainder of this section will apply to our example of the meta-mymachine layer.
393 </para>
394
395 <para>
396To get ready to build your new layer you need to do the following:
397 <orderedlist>
398 <listitem><para>
3991.Get the environment ready for the build by sourcing the environment script. The environment script is in the Yocto Project source directory and has the string init-build-env in the file’s name. For this example, the following command gets the build environment ready:
400 <literallayout class='monospaced'>
401 /usr/local/yocto$ source poky-init-build-env yocto-build
402 </literallayout>
403When you source the script a build directory is created in the current working directory. In our example we were in the Yocto Project source directory. Thus, entering the previous command created the yocto-build directory. If you do not provide a name for the build directory it defaults to build. The build directory contains a conf directory that contains two configuration files you will need to check: bblayers.conf and local.conf.</para></listitem>
404 <listitem><para>
4051.Check and edit the resulting local.conf file. This file minimally identifies the machine for which to build the image by configuring the MACHINE variable. For this example you must set the variable to mymachine as follows:
406 <literallayout class='monospaced'>
407 MACHINE ??= “mymachine”
408 </literallayout>
409 You should also be sure any other variables in which you are interested are set. Some variables to consider are BB_NUMBER_THREADS and PARALLEL_MAKE, both of which can greatly reduce your build time if you are using a multi-threaded development system (e.g. values of 8 and j 6, respectively are optimal for a development machine that has four available cores).</para></listitem>
410 <listitem><para>
4111.Update the bblayers.conf file so that it includes the path to your new BSP layer. In this example you need to include the pathname to meta-mymachine. For example, if you created a Yocto Project Git repository named yocto in /usr/local then the BBLAYERS variable in the file would need to include the following path:
412 <literallayout class='monospaced'>
413 /usr/local/yocto/meta-intel/meta-mymachine
414 </literallayout></para></listitem>
415 </orderedlist>
416 </para>
417
418 <para>
419The variable glossary in the Poky Reference Manual at http://www.yoctoproject.org/docs/1.1/poky-ref-manual/poky-ref-manual.html#ref-variables-glos has more information on configuration variables.
420 </para>
421 </section>
422
423 <section id='building-the-image'>
424 <title>Building the Image</title>
425
426 <para>
427The Yocto Project uses the BitBake tool to build images based on the type of image you want to create. You can find more information on this tool at http://bitbake.berlios.de/manual/.
428 </para>
429
430 <para>
431The build process supports several types of images to satisfy different needs. When you issue the BitBake command you provide a “top-level” recipe that essentially starts the process off of building the type of image you want.
432 </para>
433
434 <para>
435You can find these recipes in the meta/recipes-core/images and meta/recipes-sato/images directories of the Yocto Project source tree or Git repository. Although the recipe names are somewhat explanatory, here is a list that describes them:
436 <itemizedlist>
437 <listitem><para>Base – A foundational basic image without support for X that can be reasonably used for customization.</para></listitem>
438 <listitem><para>Core – A foundational basic image with support for X that can be reasonably used for customization.</para></listitem>
439 <listitem><para>Direct Disk – An image that you can copy directory to the disk of the target device.</para></listitem>
440 <listitem><para>Live – An image you can run from a USB device or from a CD without having to first install something.</para></listitem>
441 <listitem><para>Minimal – A small image without a GUI. This image is not much more than a kernel with a shell.</para></listitem>
442 <listitem><para>Minimal Development – A Minimal image suitable for development work.</para></listitem>
443 <listitem><para>Minimal Direct Disk – A Minimal Direct Disk image.</para></listitem>
444 <listitem><para>Minimal RAM-based Initial Root Filesystem – A minimal image that has the initramfs as part of the kernel, which allows the system to find the first “init” program more efficiently.</para></listitem>
445 <listitem><para>Minimal Live – A Minimal Live image.</para></listitem>
446 <listitem><para>Minimal MTD Utilities – A minimal image that has support for the MTD utilities, which let the user interact with the MTD subsystem in the kernel to perform operations on flash devices.</para></listitem>
447 <listitem><para>Sato – An image with Sato support, a mobile environment and visual style that works well with mobile devices.</para></listitem>
448 <listitem><para>Sato Development – A Sato image suitable for development work.</para></listitem>
449 <listitem><para>Sato Direct Disk – A Sato Direct Disk image.</para></listitem>
450 <listitem><para>Sato Live – A Sato Live image.</para></listitem>
451 <listitem><para>Sato SDK – A Sato image that includes the Yocto Project toolchain and development libraries.</para></listitem>
452 <listitem><para>Sato SDK Direct Disk – A Sato SDK Direct Disk image.</para></listitem>
453 <listitem><para>Sato SDK Live – A Sato SDK Live image.</para></listitem>
454 </itemizedlist>
455 </para>
456
457 <para>
458The remainder of this section applies to our example of the meta-mymachine layer.
459 </para>
460
461 <para>
462To build the image for our meta-mymachine BSP enter the following command from the same shell from which you ran the setup script. You should run the bitbake command without any intervening shell commands. For example, moving your working directory around could cause problems. Here is the command for this example:
463 <literallayout class='monospaced'>
464/usr/local/yocto/yocto-build$ bitbake –k poky-image-sato-live
465 </literallayout>
466 </para>
467
468 <para>
469This command requests an image that has Sato support and can be run from a USB device or from a CD without having to first install anything. The build process takes significant time and includes thousands of tasks, which are reported at the console. If the build results in any type of error you should check for misspellings in the files you changed or problems with your host development environment such as missing packages.
470 </para>
471 </section>
472 </section>
473
474 <section id='modifying-a-kernel'>
475 <title>Modifying a Kernel</title>
476
477 <para>
478[WRITER'S NOTE: This section is a second example that focuses on just modifying the kernel.
479I don't have any information on this yet.
480 </para>
481
482 <para>
483Here are some points to consider though:
484 <itemizedlist>
485 <listitem><para>1.Reference http://events.linuxfoundation.org/events/embedded-linux-conference/hart</para></listitem>
486 <listitem><para>1.Reference the “Getting Started” chapter to get set up at minimum.</para></listitem>
487 <listitem><para>1.Are there extra steps I need specific to kernel development to get started?</para></listitem>
488 <listitem><para>1.What do I do to get set up? Is it a matter of just installing YP and having some pieces together? What are the pieces?</para></listitem>
489 <listitem><para>1.Where do I get the base kernel to start with?</para></listitem>
490 <listitem><para>1.Do I install the appropriate toolchain?</para></listitem>
491 <listitem><para>1.What kernel git repository do I use?</para></listitem>
492 <listitem><para>1.What is the conversion script? What does it do?</para></listitem>
493 <listitem><para>1.What do I have to do to integrate the kernel layer?</para></listitem>
494 <listitem><para>1.What do I use to integrate the kernel layer? HOB? Do I just Bitbake it?</para></listitem>
495 <listitem><para>Using the System Image Creator.]</para></listitem>
496 </itemizedlist>
497 </para>
498 </section>
499</section>
500
501<section id='user-application-development'>
502 <title>User Application Development</title>
503
504 <para>
505[WRITER'S NOTE: This section is the second major development case - developing an application.
506Here are points to consider:
507 <itemizedlist>
508 <listitem><para>1.User-space Application Development scenario overview.</para></listitem>
509 <listitem><para>1.Using the Yocto Eclipse Plug-in.</para></listitem>
510 <listitem><para>1.Back-door support.</para></listitem>
511 <listitem><para>1.I feel there is more to this area than we have captured during our two review meetings.]</para></listitem>
512 </itemizedlist>
513 </para>
514</section>
54</chapter> 515</chapter>
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