Symbian Hardware Abstraction Layer (HAL) APIs

The Symbian C++ Hardware Abstraction Layer APIs can be used to query system capabilities, share state data with other applications and register for notification of changes to system states.

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Created: vvsnaresh (15 Apr 2007)

Last edited: hamishwillee (13 Aug 2012)

These APIs are implemented in two main components:

• The Hardware Abstraction Layer (HAL)
• The System Agent Components

HAL provides a very simple to use APIs, which can query the attributes of the device, for example:

• Manufacturer: manufacturer of the device, hardware and software version number.
• Processor: processor architecture, ABI and processor speed.
• Memory: total RAM, free RAM and total ROM.
• Screen: screen dimension and display color.
• Keyboard information.

The class HAL (hal.h) derives from HALData (hal_data.h), which contains the definition of the enumeration TAttribute.

Header Required:

#include <hal.h>

Library needed:

LIBRARY hal.lib

The API itself is very small, with only three functions, all provided by the class HAL:

static TInt Get(TAttribute anAttribute, TInt& aValue);
static TInt Set(TAttribute anAttribute, TInt& aValue);
static TInt GetAll(TInt& aNumEntries, SEntry*& aData);

Some examples for getting the device attributes

1. Getting all the device attributes

   TInt numHalEntries;
    
   HAL::SEntry* halEntries;
    
   HAL::GetAll(numHalEntries, halEntries);

2. Getting one specific attribute, in this case total RAM in bytes.

   TInt ram;
    
   HAL::Get(HAL::EMemoryRAM, ram);

Some examples for setting the device attributes

TInt err = HAL::Set(HAL::ECaseSwitchDisplayOn, 1);

If a field is not settable, then the return value from the call will be one of the standard system error codes, typically KErrNotSupported.