Re: [Xenomai-help] CAN rt_dev_recvfrom

[Wolfgang Grandegger <wg@domain.hid>]

roland Tollenaar wrote:
> Hi,
> 
> Ok the issue I posted earlier regarding the read function. It seems
> that it IS recieving can messages and displaying them correctly. Only
> its behaviour is not as I expected. I thought the function
> 
> rt_dev_recvfrom
> 
> would simply perform a read one frame from a buffer (which in my
> experience holds a number of can messages) then exit.
> 
> By the look of things I will have to implement the aforementioned
> buffer myself. I.e
> 
> run rt_dev_recvfrom in a separate thread other than my periodic task
> and store an x number of messages in BUFFER that I recieve there. The
> can_read() function which I implement in the periodic task must then
> simply read the messages from BUFFER.
> 
> 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.

Wolfgang.