After a few weeks of trying and trying, we are still facing this problem. Could you get any information from the configuration above?
This is driving us crazy, because we don't really understand what can be happening.
Based on your given set-up configuration, the following is your set-up:
sweep Freq 0 : 125MHz
rising step size : 0.000061MHz
step interval : 0.008us
sweep Freq 1 :132.8125MHz
falling step size : 0.00497513MHz
step interval : 0.0640us
Since you have already set the no-dwell bits to high, then the ramp would have swept up and down. Changing the falling step interval to 8ns (equivalent falling step size = 0.000625MHz to give 0.1ms ramp period) would still be working since the lowest limit of step size is 0.12Hz.
Have you checked the initial states of your pin? Also, maybe you could check your IO_update.
Your numbers are right, that's what we want. I can assure that IO_update pin is correctly managed (otherwise, neither of the configurations would work, and others configuration we've tested as well also work fine). In fact, we can program the AD9910 to work with the 64ns and it'll work, then to 8ns and it'll stop running, but when we program it back to 64ns, it's running again; so I must think there is no pin misconfiguration. All in all, both set of registers are exactly equal save for the step interval.
We're still facing this problem. We've checked pin status and programming code, everything seems to be fine.
In fact, I find no reason for the DDS to work with a time step of 00...11 setting but not for 00...00; maybe there's some bug in the digital system of the AD9910 you're not aware of? That's the only reason I can find for now for this behaviour.
You are right that there seems to be no reason for the DDS to work on 00...11 setting but not on 00..00. I'm not sure if there's some bug in the digital system of the AD9910 because we were able to bench your set-up using the AD9910 evaluation board and the ramp was able to sweep up and down for both settings. Maybe there's some limitation on the algorithm of your code that was overlooked.
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