ARM Technical Support Knowledge Articles

How does the AHB handle LOCKed SPLITs?

Applies to: AHB

Answer

When a transfer is SPLIT the arbiter degrants and removes the SPLIT master out of the arbitration until the slave indicates that the transfer can complete. When an access is LOCKed the access cannot be interrupted by an access from another master.

The only possible way that an AHB system can handle these two requirements simultaneously is to grant a "dummy master" when the LOCKed access is SPLIT. The dummy master will only perform IDLE transactions, which are allowable during a locked transfer. To grant any other master would violate the LOCK protocol, for the arbiter to ignore the SPLIT would violate the SPLIT protocol - the dummy master is the only option.

The dummy master is also used when all masters are have received a SPLIT response (the dummy master cannot receive a SPLIT response).

It is recommended that the designer of the split-capable slave(s) makes sure that the slave monitors its HMASTLOCK input so that it doesn't return a SPLIT on a LOCKed transfer, as this serves no purpose.

Article last edited on: 2008-09-09 15:47:49

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