RAM Allocator interface

The RAM Allocator interface is used to allocate and free RAM. During ChorusOS boot and initialization, the RAM occupation is described by a RamDesc object. The ramAllocator field in the BootConf structure points to the RamDesc object. The ramAllocator field is initialized by the mkimage tool as described in "RAM Occupation".

RAM occupation is described by a particular tag value associated with each address of the physical address space. The tag can have one of the following values:

• RAM_ALLOCATED, indicating that the physical address belongs to an occupied portion of RAM

• RAM_FREE, indicating that the physical address belongs to a portion of RAM available for allocation

• RAM_NONEXISTENT, indicating that the physical address does not belong to RAM (or is not available for allocation as RAM)

Three routines are provided for managing RamDesc. These routines can be used by the bootstrap program to update RamDesc according to the target BKI.

• ram_tag()

  void ram_tag (RamDesc* ram, PhAddr paddr, Phsize size, int tag);

  The ram_tag() function attempts to change the tag values of all addresses from the address range of size size starting from paddr to the value specified by tag. The ram_tag() function only changes a tag if the initial value is RAM_FREE or RAM_NONEXISTENT. It does not change a tag if the initial value is RAM_ALLOCATED.

• ram_alloc()

  int ram_alloc (RamDesc* ram, PhAddr*, paddr, PhSize size, int align);

  The ram_alloc() function allocates a portion of available RAM, tags the corresponding address range as RAM_ALLOCATED, and returns the physical address of the allocated RAM in the variable that paddr points to. align specifies the RAM alignment constraints (in bytes), or is 0 if there are no constraints. ram_alloc() returns 1 if successful, and 0 if the allocation failed.

• ram_free()

  void ram_free (RamDesc* ram, PhAddr paddr, PhSize size);

  The ram_free() function changes the tag values for the specified range of physical addresses to RAM_FREE.