OEMAddressTable

Article
06/30/2006

OEMAddressTable defines a table that maps a 4 GB physical address space to the kernel's 512-MB unmapped space for a device. Each entry in the table consists of the virtual base address to map to, the physical base address to map from, and the number of MB to map.

The data must be declared in a READONLY section and there must be at least one non-zero entry for the structure to be valid. For x86 platforms, the first entry must identify RAM, and it must start at 0x80000000. For ARM platforms, 0x80000000 can be mapped to anything. Each entry is of the following format.

Virtual Address, Physical Address, Size.

Size must be a multiple of 4MB for x86 platforms and a multiple of 1MB for ARM platforms. The last entry of the table must be zeroed. You can leave holes between ranges but you cannot have overlapping ranges.

The only valid virtual memory mapping range is from 0x80000000 to 0x9FFFFFFF. For every entry created in the table, the kernel creates two virtual address ranges. One exists in the virtual address range from 0x80000000 to 0x9FFFFFFF and is memory that has caching and buffering enabled. The second exists in the virtual address range from 0xA0000000 to 0xBFFFFFFF and has caching and buffering disabled.

Note If you modify the RAM entry in OEMAddressTable, you need to update Config.bib if you want to use the new memory mapping. For an example on how to update the Config.bib file, see Updating Config.bib with a New RAM Mapping.

Any memory that is not mapped at boot time cannot be directly accessed by an interrupt service routine (ISR) without first calling CreateStaticMapping to map the address.

The following code example shows an implementation of OEMAddressTable for x86 platforms, which has the restriction of VA 0x80000000 = PA 0x00000000. ARM platforms do not have this restriction.

public      _OEMAddressTable

   _OEMAddressTable:
   ; 
   ; OEMAddressTable defines the mapping between Physical and Virtual Address
   ;   o MUST be in a READONLY Section
   ;   o First Entry MUST be RAM, mapping from 0x80000000 -> 0x00000000
   ;   o each entry is of the format ( VA, PA, cbSize )
   ;   o cbSize must be multiple of 4M
   ;   o last entry must be (0, 0, 0)
   ;   o must have at least one non-zero entry
   ; RAM 0x80000000 -> 0x00000000, size 64M
   dd  80000000h,    0,   04000000h
   ; FLASH and other memory, if any
   ; dd  FlashVA,      FlashPA,    FlashSize
   ; Last entry, all zeros
   dd  0   0   0

OEMAddressTable

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