ARM Technical Support Knowledge Articles

How do I calculate the offset address for my flash mounted filesystem on my Versatile Express system?

Applies to: V2P-CA15, V2P-CA15-CA7, V2P-CA5

Scenario

This Knowledge Article is intended to explain the way the NOR Flash memory is described in the pre-built Linux images supplied with the Versatile Express DVD 4.0 This Knowledge Article applies to the following CoreTiles:

Answer

The boot arguments required when specifying a flash mounted filesystem include the offset address of the filesystem with respect to the base address of flash. The memory map used by the CoreTiles listed above describe NOR Flash 0 and NOR Flash 1 as two non-contiguous blocks. The Linux 'phys-map' driver will concatenate both flash devices (NOR0 and NOR1) into one device. See image below:

The following formula should be used to calculate the flash offset address that is passed into the 'phys-map' driver. 

If (flash_address >= 0xC000000) then

flash_offset = flash_address - 0x8000000

else if (flash_address >= 0x0000000 && flash_address < 0x4000000)

flash_offset = flash_offset

For example, if the filesystem was located at the physical flash address of 0xC0000000 then the flash offset that would be passed in as a boot argument would be 0x4000000.

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