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

[Wolfgang Grandegger <wg@grandegger.com>]

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.

> 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.

Wolfgang.