A port set to admit tagged frames only will never see a BPDU, because
delivery rides the forward action and the ingress pipeline drops untagged
frames before the L2 lookup. The failure is silent and looks like a dead
receive path: the port turns edge after three seconds, the bridge elects
itself root, and nothing hints at the ingress setting. Diagnosing exactly
that cost most of a day on a live switch, with the neighbour provably
transmitting the whole time.
stp_setup() now prints one line per affected port, so the hint lands at
"stp on" and at every config replay on boot. The check runs in its own
loop after the MSTP write: port_ingress_filter_get() reads a register
into sfr_data, which the state-building loop above is still using. The
port number in the message is physical, matching what the ingress
command takes.
doc/stp.md explains why this can happen here and not on a normal bridge,
where BPDUs are consumed before any VLAN classification.
stp.rel stays at DSEG 5 with no OSEG and the image at 10498 bytes of
XDATA.
The wording read as a claim about the CPU interface in general, which is
wrong and misleading: the 8051 sits behind an ordinary port of the internal
switch and is an ordinary member of a forwarding mask - which is exactly
what this implementation relies on.
Say what is actually broken instead: the trap action, a separate mechanism
whose destination is an external CPU port these boards do not populate.
Record the measurements behind it, including the widened CPU_PMSK and both
external-CPU destinations, and add the ACL trap result - a rule matching the
group intercepts frames but does not deliver them either, which is a second,
independent path to the same conclusion.
Reported-by: vDorst
Covers enabling it, the bridge and per-port settings, how BPDUs are
delivered on this hardware (RMA forward constrained by a CPU-only static
L2 entry, since trap-to-CPU targets an external CPU these boards do not
have), the timer base, and the management failsafe - enabling STP over
the network can block the very port the management VLAN rides on, so
that part is spelled out rather than left to be discovered.
d00f