However, some hardware I have sometimes produced longer preambles
How long were they, and did they happen to coincide with short frames? It's been a long time since I've worked with 10M Ethernet PHY but I vaguely remember some non-standard implementations would lengthen the preamble instead of padding the "tail" of the frame.
The preambles were longer by a few bits (even less than 8). I didn't check which frames excatly caused this, but it happened only with one old 10 MBit switch.
It's possible that some PLLs might fail to lock in within a normal amount of time to acquire the full preamble. In which case varying the length of the preamble slightly shouldn't negatively affect receivers that are well designed to tolerate unusual conditions.
Comments
However, some hardware I have sometimes produced longer preambles
How long were they, and did they happen to coincide with short frames? It's been a long time since I've worked with 10M Ethernet PHY but I vaguely remember some non-standard implementations would lengthen the preamble instead of padding the "tail" of the frame.
The preambles were longer by a few bits (even less than 8). I didn't check which frames excatly caused this, but it happened only with one old 10 MBit switch.
It's possible that some PLLs might fail to lock in within a normal amount of time to acquire the full preamble. In which case varying the length of the preamble slightly shouldn't negatively affect receivers that are well designed to tolerate unusual conditions.