Interfacing to epcs64 from fpga

Unfortunately, the answer here is not what you're looking for...

Refer to Table 10–10: "dedicated configuration pins on the stratix iv device" on page 10-42 of chapter 10 - "configuration, design security, and remote system upgrades in stratix iv devices (https://www.altera.com/content/dam/altera-www/global/en_us/pdfs/literature/hb/stratix-iv/stx4_siv51010.pdf)" of the handbook. This shows which dedicate pins are available in user mode - see the relevant column.

The Active serial configuration pins you've connected the EPCS device to are not available in user mode. So, you cannot store the user data you're hoping to in it. It's only available for device configuration.

Stratix IV does support Remote System Upgrade which allows the FPGA to reprogram the EPCS. Read up from page 10-50 of the same doc. So, the FPGA can write (and therefore read from) an EPCS attached to these pins. Enable 'Remote' configuration mode in your project to allow access to the device. However, I don't expect this will allow you to freely read and write user data in the way you're hoping for.

This is different on newer device families but not, unfortunately, Stratix IV.

Cheers,

Alex