ARM Technical Support Knowledge Articles

Split/Retry: What is the difference between SPLIT and RETRY responses?

Applies to: AHB

Answer

Both the Split and Retry responses are used by slaves which require a large number of cycles to complete a transfer. These responses allow a data phase transfer to appear completed to avoid stalling the bus, but at the same time indicate that the transfer should be re-attempted when the master is next granted the bus.

The difference between them is that a SPLIT response tells the Arbiter to give priority to all other masters until the SPLIT transfer can be completed (effectively ignoring all further requests from this master until the SPLIT slave indicates it can complete the SPLIT transfer), whereas the RETRY response only tells the Arbiter to give priority to higher priority masters.

A SPLIT response is more complicated to implement than a RETRY, but has the advantage that it allows the maximum efficiency to be made of the bus bandwidth.

The master behaviour is identical to both SPLIT and RETRY responses, the master has to cancel the next access and re-attempt the current failed access.

See also:

Article last edited on: 2014-02-05 15:50:11

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