cc'ing beagleboard list, Kevin
thanks for the patch. A quick question for you or anyone else who is
experiencing this problem.
There is an erratum in DM3730 which results in the
EHCI USB PLL (DPLL5) not updating sufficiently frequently; this
leads to USB PHY clock drift and once the clock has drifted far
enough, the PHY's ULPI interface stops responding and USB
drops out. This is manifested on a Beagle xM by having the attached
SMSC9514 report 'Cannot enable port 2. Maybe the USB cable is bad?'
The fix is to carefully adjust your DPLL5 settings so as to
keep the PHY clock as close as possible to 120MHz over the long
term; TI SPRZ319e gives a table of such settings and this patch
applies that table to systems with a 13MHz or a 26MHz clock,
thus fixing the issue (inasfar as it can be fixed) on Beagle xM
and Overo Firestorm.
Signed-off-by: Richard Watts <firstname.lastname@example.org>
Funny, I just had a conversation with Kevin Hilman about needing to put
the DPLL rate rounding code back in for the OPP tables. This looks like
another reason why...
Could you, or anyone else who is experiencing this problem on a board with
a 26MHz oscillator try a quick test for me? I'm a little curious about
the (M, N) of (443, 12) that SPRZ319E is recommending. Could you see if
your USB problems are also solved by using (480, 13) ?
Here's the rationale. Walking through the estimates here based on
SPRZ319E, (443, 12) results in a frequency error of -166,667 Hz at the VCO
output. This is 174 ppm below the desired target rate of 960MHz. But
(480, 13) results in no frequency error.
The downside of using (480, 13) is that the PLL update interval increases
from 461 ns to 500 ns (+9%). But if the long-term drift of the DPLL is
downward, then starting at a -174 ppm error has removed 35% of the total
margin (+/- 500 ppm). This might be too naïve, but a downward drift,
seems likely given that gate delay increases as temperature increases.
Mainline is currently using (120, 13) which results in a VCO output
frequency of 240MHz -- this presumably results in increased phase noise
compared to (443, 12) and (480, 13) per SPRZ319E.