Re: [Xenomai-help] CAN rt_dev_recvfrom

[Wolfgang Grandegger <wg@domain.hid>]

Roland Tollenaar wrote:
> Hi Wolfgang,
> 
>>> Can this be confirmed or is rt_dev_recvfrom() behaving incorrectly in 
>>> my case?
>>
>> rt_dev_recvfrom() reads message frames (one at a time) from an 
>> internal socket buffer (there is actually a kernel configuration 
>> option to configure the size). If no messages are available, it will 
>> block by default, but it can also be used in non-blocking mode by 
>> using the flag MSG_DONTWAIT. It seems, that your application is trying 
>> to read messages periodically in polling mode. Either you do reading 
>> and buffering in your own thread as you suggested above or you use 
>> rt_dev_recvfrom() in non-blocking mode.
> 
> Thanks for this. I have not tried it yet but I was looking for that flag 
> in the hope that something like this would exist. I thought I had seen 
> something like it but when I tried to locate it yesterday I failed. 
> Don;t worry it is there, I just checked. Sorry.
> 
> Where can I find the buffer size option in the kernel config menu? What 
> is the default size?

On the first menu of the RT-Socket-CAN configuration options:

config XENO_DRIVERS_CAN_RXBUF_SIZE
         depends on XENO_DRIVERS_CAN
         int "Size of receive ring buffers (must be 2^N)"
         default 1024

Note that the messages are stored in "packed" format.

Wolfgang.