Arria V Hard Processor System Technical Reference Manual

ID 683011
Date 12/02/2022
Public
Document Table of Contents

3.3.3.3.2. SDRAM Clock Group

The SDRAM clock group consists of a PLL and clock gating. The clocks in the SDRAM clock group are derived from the SDRAM PLL. The SDRAM PLL can be programmed to be sourced from the HPS_CLK1 pin, the HPS_CLK2 pin, or the f2h_sdram_ref_clk clock provided by the FPGA fabric.

The FPGA fabric must be configured with an image that provides the f2h_sdram_ref_clk before selecting it as the clock source. If the FPGA must be reconfigured and the f2h_sdram_ref_clk is the clock source for the SDRAM clock group, an alternate clock source must be selected prior to reconfiguring the FPGA.

The counter outputs from the SDRAM PLL can be gated off directly under software control. The divider values for each clock are set by registers in the clock manager.

Table 14.  SDRAM PLL Output Assignments
PLL Output Counter Clock Name Frequency Phase Shift Control
SDRAM C0
ddr_dqs_base_clk

Varies

9
Yes
C1
ddr_2x_dqs_base_clk
ddr_dqs_base_clk x 2 Yes
C2
ddr_dq_base_clk
ddr_dqs_base_clk Yes
C5
h2f_user2_base_clk
osc1_clk to varies9 Yes

The following figure shows clock gating for SDRAM PLL clock group. Clock gate blocks in the diagram indicate clocks which may be gated off under software control. Software is expected to gate these clocks off prior to changing any PLL or divider settings that might create incorrect behavior on these clocks.

Figure 9. SDRAM Clock Group Divide and Gating

The SDRAM PLL output clocks can be phase shifted in real time in increments of 1/8 the VCO frequency. Maximum number of phase shift increments is 4096.

Table 15.  SDRAM Clock Group Clocks

Name

Frequency

Constraints and Notes

ddr_dqs_clk

SDRAM PLL C0

Clock for MPFE, single-port controller, CSR access, and PHY

ddr_2x_dqs_clk

SDRAM PLL C1

Clock for PHY

ddr_dq_clk

SDRAM PLL C2

Clock for PHY

h2f_user2_clock

SDRAM PLL C5

Auxiliary user clock to the FPGA fabric

9 The maximum frequency depends on the speed grade of the device.