Embedded Design Handbook

ID 683689
Date 8/28/2023
Public
Document Table of Contents

5.3.9.2.2. The cpu_resetrequest Signal

In versions 6.0 and later of the Nios® II processor, an optional cpu_resetrequest signal is available to control the reset state of the processor. This signal differs from the normal Platform Designer system-wide reset signal reset_n—the cpu_resetrequest signal resets the Nios® II processor only. The rest of the Platform Designer system remains operational. This signal holds the Nios® II processor in reset while code is moved into the Nios® II program memory.

The cpu_resetrequest signal does not cause the Nios® II processor to enter the reset state immediately. When cpu_resetrequest is held high, the Nios® II processor finishes executing any instructions currently in the pipeline, then enters reset. This process may take an indeterminate number of clock cycles, so a status signal cpu_resettaken is driven high by the Nios® II processor when it reaches the reset state. The processor holds this signal high for one cycle. The cpu_resettaken signal continues to assert periodically while the cpu_resetrequest signal is held high.

To enable the cpu_resetrequest signal, open a project in Platform Designer that contains a Nios® II processor. Double-click the Nios® II component to open the Nios® II MegaWizard interface, then click the Advanced Features page. Turn on Include cpu_resetrequest and cpu_resettaken signals to enable the signals. They appear as ports on your top-level Platform Designer system after you regenerate the system.