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<task id="GUID-16423056-C435-5C4D-BE3D-4A15F95F7F68" xml:lang="en"><title>Configuration

Tutorial </title><shortdesc>Describes the steps required in producing a ROM that will work

with Writable Data Paging (WDP). </shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody>

<context id="GUID-77EC86D2-A74E-574C-868E-4304668A3863"><p>Writable Data Paging

(WDP) allows allocated memory that is to be written e.g. stacks and heaps

to be paged in and out of the RAM pool. </p> </context>

<steps id="GUID-F19DB5BA-CC38-5C2D-A337-12F4EB85F9E3">

<step id="GUID-DE8E7A0E-DB35-58B5-A5AA-85A2BFC7301C"><cmd/>

<info>It is recommended to enable WDP kerneltrace warnings if the build is

being migrated to a data paged system. </info>

<info>This is done by setting trace bit number 60 of the kernel trace flags. </info>

<info>The UDEB version of the build has to be used in order for tracing messages

to be available. </info>

<info>Once the demand paging build is stable, then the REL version of the

build can be used. </info>

</step>

<step id="GUID-D5F19B3A-3520-576A-8D59-7E1BF29AB97B"><cmd/>

<info>Set the paging policy for pages of the core ROM image. This is done

by using the datapagingpolicy and pagingpolicy keywords in the 'ROM_IMAGE[0]

{}' block. </info>

</step>

<step id="GUID-C1DF8A12-8CB4-5E71-8247-7B8F29EE66D5"><cmd/>

<info>Next, the data paging for ROFS images is enabled by using datapagingoverride

and pagingoverride keywords for each ROFS partition that contains executables

that should use data paging. This is done by adding the keywords into each

relevant 'ROM_IMAGE[&lt;partion&gt;] {}' block. </info>

</step>

<step id="GUID-A13FBB84-3885-5A49-9BA9-698F65CBF1BF"><cmd/>

<info>In order for a ROM to support data paging, it has to have a media driver

that supports data paging. </info>

</step>

</steps>

<result id="GUID-9565A808-C86C-57CF-931E-2684A382D5E2"><p>The output of this

tutorial will be a configuration that allows the ROM build to use demand paging. </p> <p> <note> This

tutorial only describes how to configure the general paging behaviour.</note> </p> </result>

<example id="GUID-9A892A74-0823-57D7-A146-BC8E14508B99"><title>Example OBY

configuration file</title> <p>Below is a typical OBY file that uses data paging,

XIP ROM and code paging: </p> <codeblock id="GUID-1A753A2E-3846-51BC-AF30-06A53785589C" xml:space="preserve">// MyDPConfig.oby 

// 

// The section below is used to specify if XIP ROM paging is to be implemented.

#if !defined PAGED_ROM 

#define PAGED_ROM 

#endif 

// The section below is used when code paging is to be implemented.

#if !defined USE_CODE_PAGING 

// Comment out the next line if code paging is wanted 

#define USE_CODE_PAGING 

#endif

#if !defined CODE_PAGING_FROM_ROFS 

// Comment out the next line if code paging from primary rofs is wanted 

#define CODE_PAGING_FROM_ROFS 

#endif 

// The section below is used to configure the RAM pages for writable data paging.

ROM_IMAGE[0] { 

pagedrom 

compress 

//                 Min   Max   Young/Old 

//                 Live  Live  Page 

//                 Pages Pages Ratio 

demandpagingconfig 256         512            3 

pagingoverride defaultpaged 

// The section below specifies if the default paging policy is to used.

#if defined USE_CODE_PAGING && !defined USE_DATA_PAGING 

codepagingpolicy defaultpaged 

#endif

#if defined USE_DATA_PAGING 

#if defined USE_CODE_PAGING 

codepagingpolicy defaultpaged 

#endif

datapagingpolicy defaultpaged 

#endif 

}

#if defined CODE_PAGING_FROM_ROFS || defined USE_DATA_PAGING 

ROM_IMAGE[1] { 

pagingoverride defaultpaged 

}

#endif 

</codeblock> <p>The OBY file that determined the start of the primary ROFS

partition, for example base.iby, would then be adjusted thus: </p> <codeblock id="GUID-7C438B69-DEB8-5598-A338-9707FA23F758" xml:space="preserve">

#if defined(_NAND) || defined(_NAND2) 

#if !defined PAGED_ROM || defined CODE_PAGING_FROM_ROFS || defined USE_DATA_PAGING 

REM Start of ROFS image 

ROM_IMAGE[1] { 

#endif 

#endif </codeblock> <p> <note> Make sure to include media drivers that can

support writable data paging.</note>  </p> </example>

<postreq id="GUID-DFC44549-2B7B-5D4F-9686-7E7BEA7E430A"><p>This tutorial only

covers the configuration of the general demand paging parameters. To see how

to make individual executables pageable see (<xref href="GUID-16423056-C435-5C4D-BE3D-4A15F95F7F68.dita#GUID-16423056-C435-5C4D-BE3D-4A15F95F7F68/GUID-9A892A74-0823-57D7-A146-BC8E14508B99">the

the writable data paging ROM</xref>  </p> </postreq>

</taskbody><related-links>

ROM tutorial</linktext></link>

</related-links></task>