DocID018909 Rev 11
RM0090
Flexible memory controller (FMC)
1669
If the next access is sequential and the current access crosses a bank boundary, the
SDRAM controller activates the first row in the next bank and initiates a new read/write
command. Two cases are possible:
•
If the current bank is not the last one, the active row in the new bank must be
precharged. At a bank boundary, the automatic activation of the next row is supported
for all rows/columns and data bus width configuration.
•
For 13-bit row address, 11-bit column address, 4 internal banks and bus width 32-bit
SDRAM memories, if the current bank is the last one and the selected SDRAM device
is connected to Bank 1, the SDRAM controller continues to read/write from the second
SDRAM device (assuming it has been initialized):
a) The SDRAM controller activates the first row (after precharging the active row, if
there is already an active row in the first internal bank, and initiates a new
read/write command.
b) If the first row is already activated, the SDRAM controller just initiates a read/write
command.
Note:
At bank boundary, if the current bank is the last one, the automatic activation of the next row
is supported only when addressing 13-bit rows, 11-bit columns, 4 internal banks and 32-bit
data bus SDRAM devices. Otherwise, the SDRAM address range is violated and an AHB
error is generated.
SDRAM controller refresh cycle
The Auto-refresh command is used to refresh the SDRAM device content. The SDRAM
controller periodically issues auto-refresh commands. An internal counter is loaded with the
COUNT value in the register FMC_SDRTR. This value defines the number of memory clock
cycles between the refresh cycles (refresh rate). When this counter reaches zero, an
internal pulse is generated.
If a memory access is ongoing, the auto-refresh request is delayed. However, if the memory
access and the auto-refresh requests are generated simultaneously, the auto-refresh
request takes precedence.
If the memory access occurs during an auto-refresh operation, the request is buffered and
processed when the auto-refresh is complete.
If a new auto-refresh request occurs while the previous one was not served, the RE
(Refresh Error) bit is set in the Status register. An Interrupt is generated if it has been
enabled (REIE = ‘1’).
If SDRAM lines are not in idle state (not all row are closed), the SDRAM controller generates
a PALL (Precharge ALL) command before the auto-refresh.
If the Auto-refresh command is generated by the FMC_SDCMR Command Mode register
(Mode bits = ‘011’), a PALL command (Mode bits =’ 010’) must be issued first.
37.7.4
Low power modes
Two low power modes are available:
•
Self-refresh mode
The auto-refresh cycles are performed by the SDRAM device itself to retain data
without external clocking.
•
Power-down mode
The auto-refresh cycles are performed by the SDRAM controller.