System Control Blocks

A board-specific configuration must define two references to linking area objects where global system control blocks are allocated:

• supervisor_context_area_ref specifies the area where supervisor address space global control blocks will be allocated.

• user_context_area_ref specifies the area where the memory for user thread private data will be allocated.

For example, the SBC8260 board-specific configuration defines supervisor_context_area_ref as a reference to ram_area:

<definition name='supervisor_context_area_ref'>
			<description>reference to the address range where global system 
				control blocks must be allocated</description>
			<type name='Area' ref-only='yes' />
			<ref name='ram_area' />
</definition>

The mkimage tool will allocate an address range for supervisor address space control blocks in ram_area (as well as the address ranges for all segments link-edited into it).

Two configurations for user_context_area_ref are defined for the SBC8260 board.

• When the micro-kernel is configured with the memory management module implementing the flat memory model (that is, when the value of the VIRTUAL_ADDRESS_SPACE configuration variable is false), user_context_area_ref is defined as a reference to ram_area:

  <definition name='user_context_area_ref'>
  			<description>reference to the address range where user software 
  					registers must be allocated</description>
  			<condition><not><var name='VIRTUAL_ADDRESS_SPACE' /></not></condition>
  			<type name='Area' ref-only='yes' />
  				<ref name='ram_area' />
  </definition>

  mkimage allocates user thread private data in ram_area.

• When the micro-kernel is configured with one of memory management modules implementing the virtual memory model (that is, when the value of the VIRTUAL_ADDRESS_SPACE configuration variable is true), user_context_area_ref defines a specific address range (linking area) in the user virtual address space:

  <definition name='user_context_area'>
  			<description>address range where user software registers must 
  				be allocated</description>
  			<condition><var name='VIRTUAL_ADDRESS_SPACE' /></condition>
  			<type name='Area' />
  			<value field='virtual'><true /></value>
  			<value field='private'><false /></value>
  			<value field='addr'><const>0xeffff000</const>></value>
  			<value field='size'><const>0x00001000</const></value>
  </definition>
  
  <definition name='user_context_area_ref'>
  			<description>reference to the address range where user software registers 
  				must be allocated</description>
  			<condition><var name='VIRTUAL_ADDRESS_SPACE' /></condition>
  			<type name='Area' ref-only='yes' />
  			<ref name='user_context_area' />
  </definition>