On 04/28/2016 02:21 PM, Florian Feldbauer wrote:
On 04/28/2016 01:36 PM, Taceant Omnes wrote:
On 26 April 2016 at 08:07, florian.feldbauer85 via BeagleBoard
<[email protected]> wrote:
I did some further tests.
Actually none of the screens from my scope looks like I would
expect it...
Picture 1 shows the result, if I try to read something on the bus
with a 14s
timeout (nothing was sended on the bus...)
Pic1
Picture 2 shows the same, but this time there were messages send
over the
bus. After 49 bytes, the beagle bone toggles the DE/!RE gpio to
high for
unknown reasons (the test program is still reading from the UART
interface)
Pic2
Picture 3 shows the test, where the BeagleBone is sending
Pic3
Your scope picture #3 does appear to show data being sent, however you
seem to say that your picture #2 portrays a test in which you received
49 bytes, however I don't see any sign of data being received in that
picture. Maybe I am missing something.
in all 4 picture from my 2nd post, channel 4 (green) shows one of
the two data lines of the bus.
Looking at #2 one can see, that this signal is starting toggling
shortly before
the DE/RE signal goes high. That's the 49 bytes I receive. After that
the data line
is still toggling araound but no longer between 0 and 1 but something
in between,
because now, there are two devices sending on the bus. One is still
the PC which
sends random data, the other one is the BeagleBone sending a constant
0...
(TX and DE/RE are constant high)
I am not an expert in these things, but my current understanding is
that what the 485 driver provides extra to what the UART driver does
is the automatic switch of the driver enable pin. One test I would
suggest, a test I have done myself, is to send and receive data with
485 using the UART driver. In this case the DE/RE needs to be set
manually. I do it using echo to /sys/class/gpio. Once that is working
well you could start test usinging the 485 driver. You should be able
to use your existing rs485_test.c program for that.
@Alex: I recommend, you read my mail ;-)
I did not look into the kernel source nor am I sure which driver is
used in my Setup,
but the problem is not the "rs485-rts-active-high" flag
As Micka and Alex said the 4.1 and 4.4 driver do not have 485 support
enabled. Per an email by Robert you need to enable the OMAP serial
kernel configuration option and rebuild the kernel.
I'm still a bit puzzled how "rs485 is not supported" looks like...
For me, being able to send and receiving data is quiet the
contrary of "not supported".
Where can I find the sources of the kernel used in the
debian-jessie-console 8.4 image
from April 07 in order to rebuild it? (I prefer changing as less as
possible, thus I'd like
to use the exact same kernel source tree as it is now)
Just found the link to Roberts script-repo at github..
I will rebuild the kernel with the OMAP driver and test the RS485
interface again...
Florian
Best regards,
Florian
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