Functional Description
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Responding to Address Transfers
When the Falcon pair detects an address transfer that it is to respond to, it
asserts AACK_ immediately if there is no uncompleted PowerPC 60x bus
data transfer in process. If there is one in process, then 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,
it 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 and External 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
is available.
Data Parity
The Falcon pair has 8 DP pins (4 per Falcon) for generating and checking
60x data bus parity. In addition, each Falcon has a DPERR_ pin to provide
real-time data parity error notification for its half of the 60x data bus.
During read cycles that access the Falcon pair, the pair generates the
correct value on DP0-DP7 so that each data byte lane along with its
corresponding DP signal has odd parity. This can be changed on a lane
basis to even parity by software bits that can force the generation of wrong
(even) parity.
During write cycles to the Falcon pair, each Falcon in the pair checks each
of its four 60x data byte lanes and the corresponding DP signal for odd
parity. If any of the four lanes has even parity, that Falcon logs the error in
the CSR and can generate a machine check if so enabled. In addition to