Cyclone® V Hard Processor System Technical Reference Manual

ID 683126
Date 8/28/2023
Public
Document Table of Contents

5.3.2.4. Initialization Phase

In this phase, the FPGA prepares to enter user mode. The internal oscillator in the FPGA portion of the device is the default clock source for the initialization phase. Alternatively, the configuration image can specify the CLKUSR or the DCLK pins as the clock source. The alternate clock source controls when the FPGA enters user mode.

If DCLK is selected as the clock source, software uses the DCLK count (dclkcnt) register to drive DCLK pulses to the FPGA. Writing to the cnt field of the dclkcnt register triggers the FPGA manager to generate the specified number of DCLK pulses. When all of the DCLK pulses have been sent, the dcntdone bit of the DCLK status (dclkstat) register is set to 1. Software polls the dcntdone bit to know when all of the DCLK pulses have been sent.

Note: Before another write to the dclkcnt register, software needs to write a value of 1 to the dcntdone bit to clear the done state.

The FPGA user I/O pins are still tri-stated in this phase. When the initialization phase completes, the FPGA releases the optional INIT_DONE pin and an external resistor pulls the pin high.