Re: read() question from newbie

[Wolfgang Grandegger <wg@grandegger.com>]

On 04/19/2012 01:10 AM, Michael Economides wrote:
> Hi Wolfgang,
> 
> I checked and the Freescale BSP I'm using is based on Linux version
> 2.6.24.7-rt21

Do you need rt? Anyway, IIRC, the MPC5121EADS board is supported by the
mainline kernel:

http://lxr.linux.no/#linux+v3.3.2/arch/powerpc/boot/dts/mpc5121ads.dts

There is no need to use the old kernel from Freescale's LTIB
distribution, which uses a special and old Socket-CAN implementation.

Wolfgang.


> On Wed, Apr 18, 2012 at 1:32 PM, Wolfgang Grandegger <wg@grandegger.com> wrote:
>> Hi Michael,
>>
>> On 04/18/2012 10:13 PM, Michael Economides wrote:
>>> Hi Oliver,
>>>
>>> Looking on my scope, it does seem like the baudrate is a little off.
>>>
>>> Here are the commands I use to set up my CAN interface on my Linux board:
>>>
>>> insmod -m candev;
>>
>> Oops, you are using a very very old version of insmod. Are you using
>> Linux 2.4.x? I do remember using "-m" with old Linux 2.4 distributions.
>>
>>> insmod -m mscan-mpc52xx;
>>> insmod -m can;
>>> insmod -m can-raw
>>> ifconfig can0 up;
>>>
>>> ./cantest can0 baud 1000000;
>>>
>>> This "cantest" program uses:
>>>
>>>  ifr.ifr_ifru.ifru_ivalue = baudrate;
>>> ret = ioctl(s, SIOCSCANBAUDRATE, &ifr);
>>>
>>> to set the baudrate.  But it seems from reading other discussions,
>>> that this is not the correct way to set baud rate.
>>
>> That's right, in case you are using a recent kernel version.
>>
>>> I am using the MPC5121 from Freescale, in case that is relevant.
>>
>> What Linux kernel version do you use? Where did you get the drivers
>> above from?
>>
>> Wolfgang.
>>
>>> On Mon, Apr 16, 2012 at 11:08 PM, Oliver Hartkopp
>>> <socketcan@hartkopp.net> wrote:
>>>> On 17.04.2012 06:16, Michael Economides wrote:
>>>>
>>>>
>>>>>>
>>>>>> I assume there is a CAN bus problem:
>>>>>>
>>>>>> - wiring (CAN_L/CAN_H)
>>>>>> - correct CAN termination (2x 120 Ohms)
>>>>>> - different bitrate
>>>>>>
>>>>>
>>>>> I think you are right, but I have checked that, it looks ok.  I will
>>>>> check again.
>>>>>
>>>>> I am using a PCAN USB adapter, and the PCAN software says there is an
>>>>> "acknowledge error" when it sends a frame to my Linux board.
>>>>
>>>>
>>>> This is an indication for a missing counterpart CAN node:
>>>>
>>>> - Wrong connection wiring
>>>> - Wrong termination
>>>> - Wrong bitrate
>>>>
>>>>>
>>>>> When the Linux board tries to send a frame to PCAN, the PCAN software
>>>>> says "form error acknowledge delimiter".
>>>>>
>>>>> It seems this is the same error in both cases, just worded differently.
>>>>
>>>>
>>>> Yes. But this means the same regarding the obvious problems.
>>>>
>>>>>
>>>>> In your opinion, is this most likely a hardware issue?  Or is there
>>>>> still some way I could be doing something wrong at the software level?
>>>>
>>>>
>>>> Did you swap CAN_H / CAN_L ??
>>>>
>>>> It's definitely one of the three points above. No SW problem ...
>>>>
>>>> Try to add a third CAN node - if you have one.
>>>>
>>>> Regards,
>>>> Oliver
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>>
> 
>