Atmel Evaluation Kit AT91SAM9X25-EK AT91SAM9X25-EK Data Sheet
Product codes
AT91SAM9X25-EK
450
SAM9X25 [DATASHEET]
11054E–ATARM–10-Mar-2014
The arbitration mechanism reduces latency when conflicts occur, i.e., when two or more masters try to access the
SDRAM device at the same time.
SDRAM device at the same time.
The arbitration type is round-robin arbitration. This algorithm dispatches the requests from different masters to the
SDRAM device in a round-robin manner. If two or more master requests arise at the same time, the master with the
lowest number is serviced first, then the others are serviced in a round-robin manner. To avoid burst breaking and to
provide the maximum throughput for the SDRAM device, arbitration may only take place during the following cycles:
SDRAM device in a round-robin manner. If two or more master requests arise at the same time, the master with the
lowest number is serviced first, then the others are serviced in a round-robin manner. To avoid burst breaking and to
provide the maximum throughput for the SDRAM device, arbitration may only take place during the following cycles:
1.
Idle cycles: When no master is connected to the SDRAM device.
2.
Single cycles: When a slave is currently doing a single access.
3.
End of Burst cycles: When the current cycle is the last cycle of a burst transfer. For bursts of defined length, pre-
dicted end of burst matches the size of the transfer. For bursts of undefined length, predicted end of burst is
generated at the end of each four beat boundary inside the INCR transfer.
dicted end of burst matches the size of the transfer. For bursts of undefined length, predicted end of burst is
generated at the end of each four beat boundary inside the INCR transfer.
4.
Anticipated Access: When an anticipate read access is done while current access is not complete, the arbitration
scheme can be changed if the anticipated access is not the next access serviced by the arbitration scheme.
scheme can be changed if the anticipated access is not the next access serviced by the arbitration scheme.
Figure 30-25.Anticipate Precharge/Active Command in Bank 2 during Read Access in Bank 1
NOP
READ
NOP
0
NOP
PRECH
ACT
READ
1
1
2
Anticipate command, Precharge/Active Bank 2
Trp
Read access in Bank 1
SDClK
A[12:0]
COMMAND
BA[1:0]
DQS[1:0]
Da
Db
Dc
Dd
De
Df
Dg
Dh
Di
Dj
Dk
Dl
D[15:0]
3
DM1:0]