I’m using bpf to send and receive the EtherCat frame,but there are something strange than when I send a broadcast ECAT frame and this frame is less then 60 bytes,I can’t receive the frame form the slave, but I add a command ‘nop’ to fill the frame size over 60 bytes ,I can receive from slave. I am using QNX6.5 and the ethernet card rtl8139. And also when I use rtl8169,there is no problem like this.
See en.wikipedia.org/wiki/Ethernet_frame and search for “runt”. Ethernet does not support packets less than 64 bytes.