Re: CAN messages being lost on i.MX25 with flexcan

[Wolfgang Grandegger <wg@grandegger.com>]

On 04/19/2012 01:58 PM, Martin Kozusky wrote:
> Dne 19.4.2012 13:44, Wolfgang Grandegger napsal(a):
>> On 04/19/2012 01:21 PM, Martin Kozusky wrote:
>>> Dne 19.4.2012 12:54, Wolfgang Grandegger napsal(a):
>>>> On 04/19/2012 12:04 PM, Martin Kozusky wrote:
>>>>> Hello,
>>>>> I'm using Voipac i.MX25 module with flexcan, kernel 2.6.38.9.
>>>>> I'm sending the data at 250kbps, around 1100 msgs/sec. When I
>>>>> enable the
>>>>> canbus interface (canconfig can0 start), CPU load is higher, that is
>>>>> understandable, there are many interrupts. I'm not doing anything else
>>>>> then using recvmsg (or recvmmsg which is little better), but some
>>>>> messages are still lost (around 1500 messages lost from 467 000 being
>>>>> send from another source). When I start doing something (like  "cat
>>>>> /proc/interrupts",  or write to file), many more messages are lost.
>>>>>
>>>>> Do you have any idea how to fix this? I need to make some CAN messages
>>>>> logger and I cannot lose any message (idealy :) So I made big
>>>>> buffer in
>>>>> my program so that I don't need to write the messages into the file
>>>>> while "recording" is enabled, after "recording" is switched off, I
>>>>> write
>>>>> the buffer into the file, but that is still not good enough.
>>>>> Is there any way how to write to some buffer directly in flexcan
>>>>> driver
>>>>> (the best would be in the IRQ routine) and then read messages from
>>>>> this
>>>>> buffer in my program?
>>>>> Or are just interrupts lost when doing something else in the system
>>>>> and
>>>>> I cannot fix this? Or can I somehow specify that "can rx
>>>>> interrupts" has
>>>>> highest prioroty?
>>>>
>>>> Do you already know where the packets are dropped (get lost). Maybe
>>>> your
>>>> user space app is simply not faster enough to process them in time. You
>>>> can check that with the candump option "-d".
>>>
>>> Hello Wolfgang,
>>> I don't know where it gets lost. But I'm just making select() and
>>> recvmmsg in my app now.
>>> Now when I'm trying candump -d, it shows messages and between that:
>>>
>>>    can0  18FFC33D  [8] 4A E6 00 00 03 00 00 F6
>>>    can0  1CEFB8F3  [8] 34 42 23 3D 8C 01 00 00
>>> DROPCOUNT: dropped 245 CAN frames on 'can0' socket (total drops 30886)
>>>    can0  18FF0AEF  [8] 70 76 46 7C A7 9E 2A 6A
>>>    can0  18FF0AF0  [8] B0 7E FB 7D A7 DC 27 69
>>>    can0  18FEBF0B  [8] F5 03 79 81 69 74 6E 79
>>>
>>> I've sent around 40 000 messages.
>>> Does this help somehow to identify where the problem is?
>>
>> Yes, you are loosing messages because your app is not faster enough.
>>
>>> I found out that if I (in my program) don't printf every frame, then
>>> dropcount is better, so I think when candump would only show dropps and
>>> not every frame then it would also get better.
>>
>> printf takes time, of course. Therefore everything which makes your app
>> reading the messages faster will help including increasing the
>> scheduling priority of the process/thread. Also increasing the size of
>> the receive buffer may help. Try candump with the "-r" option.
> 
> I tried -r 10000000
> 
> and the result was that dropping started some time later then it would
> normaly. From 467 000 packets, total drops was 103064. That is better
> ratio than before. But few times, my system was stucked for a while,
> then it recovered and continued to work. So I will try to use this
> buffer size in my program, without printf and I will see how many
> packets I lose.

If other activities delay your app too much, your are in trouble. Proper
thread priorities may help.

> Is there a way how to get actual used size of the buffer?

getsockopt?

>>> This is my /proc/interrupts
>>>
>>> root@vmx25 /opt$ cat /proc/interrupts
>>>             CPU0
>>>    0:          0           -  spi_imx
>>>    5:      32827           -  IMX-uart
>>>    9:        129           -  sdhci
>>>   13:          0           -  spi_imx
>>>   25:          5           -  imxdi_rtc
>>>   33:      12168           -  mxc_nand
>>>   34:          1           -  mxc-sdma
>>>   37:     109275           -  ehci_hcd:usb1
>>>   43:    1624971           -  can0
>>>   46:          0           -  mxcadc
>>>   54:     195357           -  i.MX Timer Tick
>>> 164:          0           -  ESDHCI card 0 detect
>>> Err:          0
>>
>> In a first place, I don't think your are loosing messages because they
>> are not read-out faster enough from the CAN controller.
>>
>>> I have another problem - when I send messages and nobody is acking them
>>> (no other device on CANbus), system stops responding until I put another
>>> device onto CANbus, but I think I should start new thread with this.
>>
>> What kernel version do you use? Do you use the flexcan driver from that
>> kernel? The problem is bus errors coming at high rate.
> 
> I'm using 2.6.35.9 Preempt, the flexcan.c driver is original.

IIRC, that kernel version did not include the flexcan driver. It entered
with 2.6.36. Anyway, maybe the following patch helps:

  http://patchwork.ozlabs.org/patch/130761/

Wolfgang.