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Honored Contributor I

Cyclone V AS configuration using Micron MT25Q

I have a card with aCyclone V that is using Active Serial Configuration from a Micron N25Q(128Mbit) flash. 

Recently i have hadto switch flash to Micron MT25Q, due to the fact that N25Q is end-of-life. 


The problem I havenow is that the FPGA on some of my boards does not configure, whereas it isalways configuring ok on other boards. 


On the boards thatdo not configure properly, the configuration works ok if I put a probe on theflash clock, or if I solder on a 10pF capacitor between the flash clock andground, or if the board is warmed up. 

So it seems to be atiming problem on the interface between the flash and the FPGA. 


The FPGA is clockingdata out on the falling edge of the clock, and in on the falling edge of theclock. 

The flash isclocking data out on the falling edge of the clock, and in on the rising edgeof the clock. 


The clock frequencyis 9.8 MHz, so there should be no problem meeting setup times. 

However, there couldbe a problem with hold time on data going from flash to FPGA, given that datais clocked out on falling edge from the flash, and clocked into the FPGA on thefalling edge. 

But - the clock iscoming from the FPGA, the flash has a clock to out of at least 1.5ns (measuredvalue in lab is 2-2.5ns), and the FPGA has a hold time of 0ns, according to theCyclone V data sheet. 


The clock looksbeautiful - perfect flanks, very little noise. 

There is no noise onany of the power rails. 


When the FPGA is notconfiguring, I see that CONF_DONE stays low, but nSTATUS is pulled low every~3.7ms. 


I'm familiar withthis very nice thread:

This thread hastempted me to use Windbond flash instead of Micron, but I'm concerned that thismay not improve my situation. 

After all, theproblems I'm having is only on some of my boards, not on all of them. 


I'm also aware thatAltera has recently added support for Micron MT25, but unfortunately this onlyapplies to 256Mbit and above, and at the moment these devices are hard to get. 


So, I'm reaching outto all of you experts in this forum; do you have any suggestions, ideas,thoughts, comments? 

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