Atmel Evaluation Kit AT91SAM9X25-EK AT91SAM9X25-EK Data Sheet
Product codes
AT91SAM9X25-EK
449
SAM9X25 [DATASHEET]
11054E–ATARM–10-Mar-2014
30.5.4.4 Reset Mode
The reset mode is a feature of the DDR2-SDRAM. This mode is activated by setting the low-power command bits (LPCB)
to 11 and the clock frozen command bit (CLK_FR) to 1.
to 11 and the clock frozen command bit (CLK_FR) to 1.
When this mode is enabled, the DDRSDRC leaves normal mode (mode == 000) and the controller is frozen. Before
enabling this mode, the end user must assume there is not an access in progress.
enabling this mode, the end user must assume there is not an access in progress.
To exit reset mode, the low-power command bits (LPCB) must be set to “00”, clock frozen command bit (CLK_FR) set to
0 and an initialization sequence must be generated by software. See
0 and an initialization sequence must be generated by software. See
30.5.5 Multi-port Functionality
The SDRAM protocol imposes a check of timings prior to performing a read or a write access, thus decreasing the
performance of systems. An access to SDRAM is performed if banks and rows are open (or active). To activate a row in
a particular bank, it has to de-active the last open row and open the new row. Two SDRAM commands must be
performed to open a bank: Precharge and Active command with respect to Trp timing. Before performing a read or write
command, Trcd timing must checked.
performance of systems. An access to SDRAM is performed if banks and rows are open (or active). To activate a row in
a particular bank, it has to de-active the last open row and open the new row. Two SDRAM commands must be
performed to open a bank: Precharge and Active command with respect to Trp timing. Before performing a read or write
command, Trcd timing must checked.
This operation represents a significative loss. (see
Figure 30-24.Trp and Trcd Timings
The multi-port controller has been designed to mask these timings and thus improve the bandwidth of the system.
DDRSDRC is a multi-port controller since four masters can simultaneously reach the controller. This feature improves
the bandwidth of the system because it can detect four requests on the AHB slave inputs and thus anticipate the
commands that follow, PRECHARGE and ACTIVE commands in bank X during current access in bank Y. This allows Trp
and Trcd timings to be masked (see
the bandwidth of the system because it can detect four requests on the AHB slave inputs and thus anticipate the
commands that follow, PRECHARGE and ACTIVE commands in bank X during current access in bank Y. This allows Trp
and Trcd timings to be masked (see
). In the best case, all accesses are done as if the banks and rows were
already open. The best condition is met when the four masters work in different banks. In the case of four simultaneous
read accesses, when the four banks and associated rows are open, the controller reads with a continuous flow and
masks the cas latency for each different access. To allow a continuous flow, the read command must be set at 2 or 3
cycles (cas latency) before the end of current access. This requires that the scheme of arbitration changes since the
round-robin arbitration cannot be respected. If the controller anticipates a read access, and thus before the end of current
access a master with a high priority arises, then this master will not serviced.
read accesses, when the four banks and associated rows are open, the controller reads with a continuous flow and
masks the cas latency for each different access. To allow a continuous flow, the read command must be set at 2 or 3
cycles (cas latency) before the end of current access. This requires that the scheme of arbitration changes since the
round-robin arbitration cannot be respected. If the controller anticipates a read access, and thus before the end of current
access a master with a high priority arises, then this master will not serviced.
NOP
PRCHG
NOP
ACT
NOP
READ
BST
NOP
0
3
Trp
Trcd
Latency =2
4 cycles before performing a read command
SDCLK
A[12:0]
COMMAND
BA[1:0]
DQS[1:0]
D[15:0]
DM1:0]
Da
Db