External Memory Interface Handbook Volume 3: Reference Material

ID 683841
Date 7/24/2019
Document Table of Contents

4.5.5. Sequencer

The sequencer employs an RTL-based state machine which assumes control of the interface at reset (whether at initial startup or when the IP is reset) and maintains control throughout the calibration process. The sequencer relinquishes control to the memory controller only after successful calibration.

The sequencer consists of a calibration state machine, together with a read-write (RW) manager, PHY Manager, and PLL Manager.

Figure 141. Sequencer Architecture

Figure 142. Calibration State Machine Stages

RW Manager

The read-write (RW) manager encapsulates the protocol to read and write to the memory device through the Altera PHY Interface (AFI). It provides a buffer that stores the data to be sent to and read from memory, and provides the following commands:

  • Write configuration—configures the memory for use. Sets up burst lengths, read and write latencies, and other device specific parameters.

  • Refresh—initiates a refresh operation at the DRAM. The sequencer also provides a register that determines whether the RW manager automatically generates refresh signals.

  • Enable or disable multi-purpose register (MPR)—for memory devices with a special register that contains calibration specific patterns that you can read, this command enables or disables access to the register.

  • Activate row—for memory devices that have both rows and columns, this command activates a specific row. Subsequent reads and writes operate on this specific row.

  • Precharge—closes a row before you can access a new row.
  • Write or read burst—writes or reads a burst length of data.
  • Write guaranteed—writes with a special mode where the memory holds address and data lines constant. Intel guarantees this type of write to work in the presence of skew, but constrains to write the same data across the entire burst length.

  • Write and read back-to-back—performs back-to-back writes or reads to adjacent banks. Most memory devices have strict timing constraints on subsequent accesses to the same bank, thus back-to-back writes and reads have to reference different banks.

  • Protocol-specific initialization—a protocol-specific command required by the initialization sequence.

PHY Manager

The PHY Manager provides access to the PHY for calibration, and passes relevant calibration results to the PHY. For example, the PHYManager sets the VFIFO and LFIFO buffer parameters resulting from calibration, signals the PHY when the memory initialization sequence finishes, and reports the pass/fail status of calibration.

PLL Manager

The PLL Manager controls the phase of capture clocks during calibration. The output phases of individual PLL outputs can be dynamically adjusted relative to each other and to the reference clock without having to load the scan chain of the PLL. The phase is shifted by 1/8th of the period of the voltage-controlled oscillator (VCO) at a time. The output clocks are active during this dynamic phase-shift process.

A PLL counter increments with every phase increase and decrements with every phase reduction. The PLL Manager records the amount by which the PLL counter has shifted since the last reset, enabling the sequencer and tracking manager to determine whether the phase boundary has been reached.

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