Am 04.02.21 um 16:38 schrieb Patrick Menschel:
> Hi,
>
> is anyone writing to BCMSocket on the Raspberry Pi from Python3 ?
>
> I'm digging through an endianess / alignment issue on armhf platform.
>
> My testcode [1] that I wrote years ago on works on X86_64 platform but
> fails on armhf platform with OSERROR 22 "invalid argument".
Some more details.
The length on X86_64 results in 72 bytes which are consumed by bcm.
On armhf it results in 52 bytes which cause OSError: [Errno 22] Invalid
argument.
>
> Then I started concatenating bytes by hand instead of using ctypes.
>
> What I came around is that frames[0] is somehow expected to be 8 bytes
> length although it should be 16 bytes.
>
> struct bcm_msg_head {
> ...
> struct can_frame frames[0];
> };
>
> I ended up inserting padding 8 bytes instead of frames[0] value and that
> actually works.
I have to amend that, it's 4 padding bytes.
struct.pack("=IIIllllII4xIB3x8s",opcode,flags,count,ival1_sec,ival1_usec,ival2_sec,ival2_usec,can_id,nframes,can_id,can_dlc,data)
^^ padding bytes
Sending the resulting 56bytes to bcmsocket gets me a cyclic message on
armhf.
>
> That makes my overall BCMHead 40 bytes and the complete bcm message
> including the can frame 56bytes.
>
> [1] https://github.com/menschel/pysocketcan
>
Thanks,
Patrick
