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RE: RS485 userspace test


Since we don't have access to your firmware you need to run the oops 
through ksymoops to see where the problem occurs.

example: ksymoops -v vmlinux -K -L -O -m os/linux/System.map

Normally it should be possible to run any kernel but we recommend
the kernels distributed with the developer board releases on


-----Original Message-----
From: owner-dev-etrax@xxxxxxx.com]On">mailto:owner-dev-etrax@xxxxxxx.com]On
Behalf Of Hansen Martin
Sent: Friday, June 07, 2002 7:56 PM
To: dev-etrax
Subject: RS485 userspace test

I have tested the new serial driver design, in the 2.4.19-pre10 kernel.
I have tested whether I can write to RS485 bus from userspace, with the
RS485 capability on
Basically I enable RS485 in kernel config.
A userspace program open the dev file /dev/ttyS3 then calls the IOCTL to
enable RS485.
I write to the dev file

That runs well if I am the only on the RS485 bus, because if I get an answer
from the device I that also is on the RS485 bus.
Then I get a kernel oops and panic. the answer comes about 10 ms after I
send my message.

I have tested it on kernel 2.4.19-pre8 + new serial patch, and on kernel
2.4.19-pre9 and pre10 without a patch.
Exact same result.

The serial port is set to 9600 parenb (8o1).

By a normal run, (that I can achieve trough a call to the same driver from
another module, and therefore kernelspace).
I get something like the ascii graphic below

         axis send    device answer

But if I do the same thing from userspace, I get this result

         axis send    device answer

As you can see the RTS line makes two short jumps when receiving the answer,
it is probably caused by the kernel going down.

If I turn off my device, so there is no answer. It looks as expected. and no
extra jumps on the RTS line.

         axis send    device answer

Attached the oops message from the pre8 version (they are similar for all

BTW: I can _not_ use the method of toggling the RTS directly from userspace,
it is too slow.

Martin Hansen
Student at SDU Sønderborg. www.sdu.dk
Writing final project at Danfoss drives A/S. http://drives.danfoss.com

Tlf: 74 88 54 62