EPCS : read electronic signature

We've struggled with a similar problem and so I'd be interested in knowing what you've found.

I've put breakpoints in alt_epcs_flash_query where it does the call:

flash->silicon_id =

epcs_read_electronic_signature(flash->register_base);

and have seen rather intermittent results, i.e. sometimes it reads the signature okay and sometimes it doesn't. It often changes its behavior when I re-download the .sof file. We are running on our own hardware with a 2C20-C8. We are using a STM serial flash M25P64V6G. We have Quartus 5.1 and Nios 5.1.

We've looked at the read sequence on a scope and when it fails it looks .... funny, it gets 0 back for the signature and other random stuff. The read signature sequence should be 40 clocks. They are being done a byte at a time which makes sense as they are coming out of a SPI controller but there is a long time between bytes, about 10 us, the clock is 12.5 MHz.

Has anyone experienced similar problems?

Mike