MECAR regulation problem upon attempted turn on after a power outage
After a power outage (on 11/04/2014) for most of the Accelerator Complex (but not MECAR), upon trying to establish a MI ramp, MECAR was show large errors on the way up and down the ramp. It was discovered that the ramp was running out of voltage.
The maximum PS voltage limit in MECAR's tiers was increased to allow provide the needed voltage. But the questioned remained: why do we need more voltage all of a sudden?
The next morning (11/05/2014), while still scratching our heads, we had MECAR rebooted... the problem went away (i.e. the additional voltage was no longer needed). This lead to the hypothesis that MECAR's PPL that locks the 1440Hz interrupt to TCLK's 720Hz event became unlocked during the power outage (TCLK went away).
#1 Updated by Kevin Martin over 5 years ago
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The PLL Frequency gain was set to -0.001. The gain is ok to lock the PLL at boot time. However, if TCLK goes away and then comes back is was not sufficient to relock the PLL. I did some testing in the micropit (using the backup MECAR) and found that increasing the gain to -0.01 works very well to lock at boot time and after losing and recovering TCLK.
The mecar_sys.c module was modified to permanently change the PLL Frequency Gain.