Digi NS9215 Ownership, Until the transaction completes, Master will not occupy the system bus

S Y S T E M C O N T RO L M O D U L E	. .
System bus arbiter..
	.

2The arbiter stops evaluating the BRR until a bus grant is issued for the previous evaluation cycle.

3The arbiter grants the bus to requesting channels, in a round-robin manner, at the rising clock edge of the last address issued for the current transaction (note that each transaction may have multiple transfers), when a SPLIT response is sampled by the arbiter, or when the bus is idling.

4Each master samples the bus grant signal (hgrant_x) at the end of the current transfer, as indicated by the hready signal. The bus master takes ownership of the bus at this time.

5The arbiter updates the hmaster [3:0] signals at the same time to indicate the current bus master and to enable the new master’s address and control signals to the system bus.

See your AMBA standards documentation for detailed information and illustrations of AMBA AHB transactions.

Ownership	Ownership of the data bus is delayed from ownership of the address/control bus.
	When hready indicates that a transfer is complete, the master that owns the
	address/control bus can use the data bus — and continues to own that data bus —
	until the transaction completes.
	Note: If a master is assigned more than one request/grant channel, these channels
	need to be set and reset simultaneously to guarantee that a non-requesting
	master will not occupy the system bus.

Locked bus sequence

Relinquishing the bus

The arbiter observes the hlock_x signal from each master to allow guaranteed back- to-back cycles, such as read-modified-write cycles. The arbiter ensures that no other bus masters are granted the bus until the locked sequence has completed. To support SPLIT or RETRY transfers in a locked sequence, the arbiter retains the bus master as granted for an additional transfer to ensure that the last transfer in the locked sequence completed successfully.

If the master is performing a locked transfer and the slave issues a split response, the master continues to be granted the bus until the slave finishes the SPLIT response. (This situation degrades AHB performance.)

When the current bus master relinquishes the bus, ownership is granted to the next requester.

If there are no new requesters, ownership is granted to the last master.

Bus parking must be maintained if other masters are waiting for SPLIT transfers to complete.

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