diff -r 89d6a7a84779 -r 25a17d01db0c Symbian3/PDK/Source/GUID-3A625B23-354E-5CB4-98CF-FF53AD724FA0.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Symbian3/PDK/Source/GUID-3A625B23-354E-5CB4-98CF-FF53AD724FA0.dita Fri Jan 22 18:26:19 2010 +0000 @@ -0,0 +1,62 @@ + + + + + +Migration +Tutorial: Demand Paging +

Demand paging is a change to how the Kernel can use RAM from Symbian platform +v9.3. This topic describes the possible results for base port.

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When demand paging is used, the contents of memory are available to a program +when they are required - i.e. 'on demand'. When the contents are no longer +required, the RAM can be used for other content. In this way, the total RAM +required to store content is less than if it were all permanently available.

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The Device Driver Guide provides Suggested +techniques for mitigating the effects of demand paging for writers +of device drivers. These recommendations can result in a more ‘multithreaded’ +base-port. This may have the following impact that needs to be considered:

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  • A base-port component +may provide services to device drivers, exposing to them a shared resource; +either hardware or software:

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    • hardware - may be a +hardware controller whose non-instantaneous operation, once initiated, cannot +be disturbed until it completes

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    • software - may be a +list of requests for services.

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  • A hardware component +has a control interface that can be used by a number of drivers. Operations +on the control interface although near instantaneous, are not atomic and cannot +be interrupted.

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In the case of the base-port component, when the state of a resource needs +to be protected from the effects of pre-emption for a non-negligible period +of time, the recommended approach is to use mutual exclusion, protecting the +resource with a mutex: unless there is any chance that the same driver may +trigger the same operation before the previous one completed. For example, +when operations are non-blocking and happen in a context different from the +initiator’s, a NFastMutex should suffice.

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An example of the hardware component situation is a set-clear control interface, +where a pair of registers (one containing the bits to be set, the other the +bits to be cleared) have to be written to produce the desired change. If the +operation is pre-empted after bits are set but before they are cleared for +a desired final output, and a new set-clear operation is initiated, the final +state of the interface may be undetermined. Pre-emption protection in this +case is achieved by simply locking the Kernel using NKern::Lock() before +the operation starts and unlocking it with NKern::Unlock() after +it completes. If the interface is to be used from an interrupt context disabling +all interrupts is sufficient to protect against thread concurrency.

+ +Migration + Tutorial: Demand Paging and Internal MMC Cards + +Migration +Tutorial: Demand Paging and Media Drivers + \ No newline at end of file