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Hi Chu,
On 2014-11-04 21:40, Shu Liu wrote:
> You can give a 3.3v directly or use a small resistor to make the
> voltage on the 4th pin of J1 higher than 3V. That should work. We
> rebooted a
Well, that is interesting, as it isn't consistent with my findings. I
guess you missed that I use a 82k5 ohms resistor as pull up. That's
where the 3,3V*(100k/(100k+82,5k)= 1.81V level on B_UART0_RX/J4.1 is
from (which I misstated as the 82k2's voltage drop of 1.4V in previous
post).
This is close to, but not surpassing, the high level voltage of U15
which is 2V at 3.3V VCC (datasheet p. 3), thus it will interpret my
B_UART0_RX as a low level. As my modification also solves the issue,
your assumption about your fix (a high level at J4.1/B_UART0_RX
(U15.2/1A)) is not true.
> board over hundreds of time by using an app on Linux. It did not
> fail a single time.
Nice, thought about doing something like that too while manually
plug/unplugging ;). Is that application available somewhere? It would be
nice to fully automate the test to really hammer this issue.
How do you notify the application of successful boot? Another BBB and
some IO's?
> We found this accidently by using serial cable and the board never
> fails
No-one can plan for good stuff, it just shows up. Nice find, I remember
having read your posting about it somewhere.
> We measured the UART3_RX(D16), UART3_TX(D15), UART4_RX(pin11 on
> header P9) and UART4_TX(pin13 on header P9). They are all 3.3V and
> they are in UART mode.
Pins configurable for UART3 is used for MMC/MII, so I guess it is UART1
on TX;D15/P9.24 and RX;D16/P9.26 you have measured?
> We removed the R165 which is the pull down resistor on the UART0_RX
> line. The UART0_RX is around 1.4V and sometimes floating. We also
> checked the device tree. The internal pull up of the UART0_RX is
> turned on.
Peculiar, as it should never float.
> We do not know why the UART0_RX is not getting 3.3V, can you please
> check the voltage on both UART0_TX and UART0_RX when U15 is
> removed?
I'll definitely look into this tomorrow. Including taking this
measurement.
> Again, If somebody can tell me how to fix it in uboot or from
> software perspective, I would really appreciate it.
Got hints or pointers on bulding uboot for BBB? There's a lot of
different how-tos/blogs out there.
Regads,
- --
Mikkel
,= ,-_-. =.
((_/)o o(\_))
`-'(. .)`-'
\_/
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