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Configuration Tutorial

Describes the steps required in producing a ROM that will work with Writable Data Paging (WDP).

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.

It is recommended to enable WDP kerneltrace warnings if the build is being migrated to a data paged system. This is done by setting trace bit number 60 of the kernel trace flags. The UDEB version of the build has to be used in order for tracing messages to be available. Once the demand paging build is stable, then the REL version of the build can be used.
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.
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[<partion>] {}' block.
In order for a ROM to support data paging, it has to have a media driver that supports data paging.

The output of this tutorial will be a configuration that allows the ROM build to use demand paging.

Note: This tutorial only describes how to configure the general paging behaviour.

Example OBY configuration file

Below is a typical OBY file that uses data paging, XIP ROM and code paging:

// 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

The OBY file that determined the start of the primary ROFS partition, for example base.iby, would then be adjusted thus:


#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

Note: Make sure to include media drivers that can support writable data paging.

This tutorial only covers the configuration of the general demand paging parameters. To see how to make individual executables pageable see (the mmp configuration tutorial).

The next step is to build the writable data paging ROM

Parent topic: Writable Data Paging Tutorial

Related tasks

Building ROM tutorial