AN 738: Intel® Arria® 10 Device Design Guidelines

ID 683555
Date 6/30/2017
Document Table of Contents

1.5.4. Clock and PLL Selection

Table 42.  Clock and PLL Selection Checklist
Number Done? Checklist Item
1   Use the correct dedicated clock pins and routing signals for clock and global control signals.
2   Use the device PLLs for clock management.
3   Analyze input and output routing connections for each PLL and clock pin. Ensure PLL inputs come from the dedicated clock pins or from another PLL.

The first stage in planning your clocking scheme is to determine your system clock requirements. Understand your device’s available clock resources and correspondingly plan the design clocking scheme. Consider your requirements for timing performance, and how much logic is driven by a particular clock.

Arria® 10 devices provide dedicated low-skew and high fan-out routing networks. They are organized in a hierarchical structure that provides up to 417 unique clock domains within the device (16 GCLKs + 92 RCLKs + 309 PCLKs). There are up to 28 fractional PLLs per device and up to 18 independently-programmable outputs per PLL. You can use 16 differential dedicated GCLK input pins or 48 to 56 single-ended clock inputs.

The dedicated clock pins drive the clock network directly, ensuring lower skew than other I/O pins. Use the dedicated routing network to have a predictable delay with less skew for high fan-out signals. You can also use the clock pins and clock network to drive control signals like asynchronous reset.

Connect clock inputs to specific PLLs to drive specific low-skew routing networks. Analyze the global resource availability for each PLL and the PLL availability for each clock input pin.

Use the following descriptions to help determine which clock networks are appropriate for the clock signals in your design:

  • The GCLK networks can drive throughout the entire device, serving as low-skew clock sources for device logic. This clock region has the maximum delay compared to other clock regions but allows the signal to reach everywhere within the device. This option is good for routing global reset/clear signals or routing clocks throughout the device.
  • The RCLK networks only pertain to the quadrant they drive into and provide the lowest clock delay and skew for logic contained within a single device quadrant.
  • IOEs and internal logic can also drive GCLKs and RCLKs to create internally generated GCLKs or RCLKs and other high fan-out control signals; for example, synchronous or asynchronous clears and clock enables.
  • PLLs cannot be driven by internally-generated GCLKs or RCLKs. The input clock to the PLL must come from dedicated clock input pins or from another pin/PLL-fed GCLK or RCLK.
  • PCLK networks are a collection of individual clock networks driven from the periphery of the Arria® 10 device. Clock outputs from the DPA block, PLD-transceiver interface, I/O pins, and internal logic can drive the PCLK networks. These PCLKs have higher skew compared to GCLK and RCLK networks and can be used instead of general purpose routing to drive signals into and out of the Arria® 10 device.

If your system requires more clock or control signals than are available in the target device, consider cases where the dedicated clock resource could be spared, particularly low fan-out and low-frequency signals where clock delay and clock skew do not have a significant impact on the design performance. Use the Global Signal assignment in the Quartus® Prime Assignment Editor to select the type of global routing, or set the assignment to Off to specify that the signal should not use any global routing resources.