It fires almost always 0x5800 for tx and 0x01 for rx
ir=0x01 means RF0N set (Rx FIFO 0 New Message)
ir=0x5800 means TEFF|TEFN|TFE
(Tx Event FIFO Full, Tx Event FIFO New Entry, Tx FIFO Empty)
It seems, that m_can_isr is called to late. I catch Fifo full and empty
flags together.
According to tcan4550 datasheet, M_CAN Revision is 3.2.1.1 ,thus >3.0
I am slightly confused by the discrepancy in Bits > 29 in m_can.c and
mcan_users_manual_v330.pdf, section 2.3.16 Interrupt Register (IR), page
20. But it is not my focus point.
