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34.6. Architecture
The SDRAM Controller connects to one or more SDRAM chips, and handles all SDRAM protocol requirements. Internal to the device, the core presents an Avalon® -MM agent ports that appears as a linear memory (flat address space) to Avalon® -MM host device.
The core can access SDRAM subsystems with:
- Various data widths (8-, 16-, 32- or 64-bits)
- Various memory sizes
- Multiple chip selects
The Avalon® -MM interface is latency-aware, allowing read transfers to be pipelined. The core can optionally share its address and data buses with other off-chip Avalon® -MM tri-state devices.
Control logic within the SDRAM core responsible for the main functionality listed below, among others:
- Refresh operation
- Open_row management
- Delay and command management
Use of the data bus is intricate and thus requires a complex DRAM controller circuit. This is because data written to the DRAM must be presented in the same cycle as the write command, but reads produce output 2 or 3 cycles after the read command. The SDRAM controller must ensure that the data bus is never required for a read and a write at the same time.