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Zynq-7000 AP SoC Technical Reference Manual www.xilinx.com 290
UG585 (v1.11) September 27, 2016
Chapter 10
DDR Memory Controller
10.1 Introduction
The DDR memory controller supports DDR2, DDR3, DDR3L, and LPDDR2 devices and consists of
three major blocks: an AXI memory port interface (DDRI), a core controller with transaction scheduler
(DDRC) and a controller with digital PHY (DDRP).
The DDRI block interfaces with four 64-bit synchronous AXI interfaces to serve multiple AXI masters
simultaneously. Each AXI interface has its own dedicated transaction FIFO.
The DDRC contains two 32-entry content addressable memories (CAMs) to perform DDR data service
scheduling to maximize DDR memory efficiency. It also contains fly-by channel for low latency
channel to allow access to DDR memory without going through the CAM.
The PHY processes read/write requests from the controller and translates them into specific signals
within the timing constraints of the target DDR memory. Signals from the controller are used by the
PHY to produce internal signals that connect to the pins via the digital PHYs. The DDR pins connect
directly to the DDR device(s) via the PCB signal traces.
The system accesses the DDR via DDRI via its four 64-bit AXI memory ports. One AXI port is
dedicated to the L2-cache for the CPUs and ACP, two ports are dedicated to the AXI_HP interfaces,
and the fourth port is shared by all the other masters on the AXI interconnect.
The DDR interface (DDRI) arbitrates the requests from the eight ports (four reads and four writes).
The arbiter selects a request and passes it to the DDR controller and transaction scheduler (DDRC).
The arbitration is based on a combination of how long the request has been waiting, the urgency of
the request, and if the request is within the same page as the previous request.
The DDRC receives requests from the DDRI through a single interface. Both reads and writes flow
through this interface. Read requests include a tag field that is returned with the data from the DDR.
The DDR controller PHY (DDRP) drives the DDR transactions.