Functional Description

PowerPC 60x Bus Interface

The Falcon pair has a PowerPC slave interface only. It has no PowerPC master interface. The slave interface is the mechanism for all accesses to DRAM, ROM/Flash, and Falcon registers/SRAM.

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Responding to Address Transfers

When the Falcon pair detects an address transfer to which it should respond, it asserts AACK_ immediately if there is no uncompleted PowerPC 60x bus data transfer in progress. If a transfer is in progress, the Falcon pair waits and asserts AACK_ coincident with the uncompleted data transfer’s last data beat if the Falcon pair is the slave for the previous data. If it is not the slave for the previous data, the Falcon pair holds off AACK_ until the CLOCK after the previous data transfer’s last data beat.

Completing Data Transfers

If an address transfer to the Falcon pair will have an associated data transfer, the Falcon pair begins a read or write cycle to the accessed entity (DRAM/ROM/Flash/internal register) as soon as the entity is free. If the data transfer will be a read, the Falcon pair begins providing data to the PowerPC 60x bus as soon as the entity has data ready and the PowerPC 60x data bus is granted. If the data transfer will be a write, the Falcon pair begins latching data from the PowerPC data bus as soon as any previously latched data is no longer needed and the PowerPC 60x data bus has been granted.

Cache Coherency

The Falcon pair supports cache coherency by monitoring the ARTRY_ control signal on the PowerPC 60x bus and behaving appropriately when it is asserted. When ARTRY_ is asserted, if the access is a read, the Falcon pair does not source the data for that access. If the access is a write, the Falcon does not write the data for that access to the DRAM array. Depending upon when the retry occurs however, the Falcon pair may cycle the DRAM even though the data transfer does not happen.

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Motorola MVME2300 Series manual PowerPC 60x Bus Interface, Responding to Address Transfers, Completing Data Transfers