ARM Technical Support Knowledge Articles

General: Why is a burst not allowed to cross a 1 kilobyte boundary?

Applies to: AHB

Answer

If an AHB slave samples HSELx at the start of a burst transaction, it knows it will be selected for the duration of the burst. Also, a slave which is not selected at the start of a burst will know that it will not become selected until a new burst is started.

1 kilobyte is the smallest area an AHB slave may occupy in the memory map. Therefore, if a burst did cross a 1 kilobyte boundary, the access could start accessing one slave at the beginning of the burst and then switch to another on the boundary, which must not happen for the above reason.

The 1 kilobyte boundary has been chosen as it is large enough to allow reasonable length bursts, but small enough that peripherals can be aligned to the 1 kilobyte boundary without using up too much of the available memory map.

See also:

Article last edited on: 2014-02-06 13:48:21

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