EP504 AHB Bus to SDRAM Controller
The AHB bus SDRAM controller provides high speed SDRAM for the system. It
features two access ports. One port interfaces directly to the AHB bus and the
other access port is optimized for system core logic such as DMA or PCI bus
The EP504 SDRAM controller contains built-in arbitration unit to allow both the
AHB CPU and system core logic to share SDRAM access. Rotating priority
scheme ensures equal sharing of the memory bandwidth.
The SDRAM controller is a high performance SDRAM controller designed for
transferring data to and from any industry standard SDRAMs or PC100/133
SDRAM DIMMs at the highest possible data rate.
The pipeline feature of the SDRAM controller allows the user port to specify the
next access address while the current data transfer is in progress. Multiple data
transfers can be cascaded together to read or write data from the SDRAM contin-
uously, without any wasted cycle between accesses.
Another performance enhancement features of the SDRAM controller is that it
uses fast page access whether there is a row hit. For each of the four internal
banks, the SDRAM controller keeps the previous accessed row open. If the new
request hits the same row, a column access is performance thus eliminate row
access time. The SDRAM controller simultaneously keeps track of four open
rows, one for each bank.
The SDRAM controller can be programmed to support different sizes and config-
urations of SDRAMs. The SDRAM device sizes supported are 64Mbits,
128Mbits, and 256Mbits. The data width per SDRAM device can be programmed
to 4, 8, 16 or 32 bits. The user can use multiple SDRAMs to build an wider mem-
The SDRAM controller is fully programmable. All access timing parameters such
as CAS latency, row-to-column delay, refresh interval, etc., are programmable to
support different speed grades of SDRAM devices and different operating fre-
quencies. All the timing parameters can be modified during run-time by a separate
access port. The timing parameters can also be set to the proper default values
during compile time so that there is no need to program them during run-time.
The user interface of the SDRAM controller is a user-friendly synchronous bus,
similar to the I960 microprocessor interface. The user provides the address for
each access and the SDRAM controller automatically generate the row (RAS) and
column (CAS) access cycles to transfer data. The user can specify single or burst
data transfer. In burst data transfer, zero wait state data bursting is supported to
maximize memory bandwidth. SDRAM refresh cycle is periodically issued by the
SDRAM controller. The refresh cycles are transparent to the AHB bus or the user
© 2001 by Eureka Technology Inc.
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