Intel Cyclone V Design Manuallines page 66

5.4.1.5. Example Code to Write and Read from All Addresses
5.4.1.6. Read/Write to HPS Register in Preloader
Use the following function:
1.
writel
AN 796: Cyclone V and Arria V SoC Device Design Guidelines
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to write to HPS register
5. Embedded Software Design Guidelines for SoC FPGAs
AN-796 | 2018.06.18