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doc: move the L2 multicast and tag word details out of the code

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Review asked for this directly: the hardware layout above port_l2mc_set()
would be better as documentation than as a comment, keeping only the two
lines that say what the function does.

doc/l2.md gains a section on static multicast entries, why delivery uses
the forward action rather than the trap, and the SMI layout of the entry.
doc/CpuPort.md gains the layout of the tag's flags and pmask words, with
the byte order trap that cost an afternoon: writing the flags constant raw
instead of through HTONS puts 0x0020 on the wire as 0x2000, which is EFID
rather than LEARN_DIS, and the ASIC then leaves the 0x8899 header on the
frame.

The comments those paragraphs came from are replaced by a pointer to the
file that now holds them.
This commit is contained in:
d00f
2026-08-18 23:29:10 +02:00
committed by d00f
parent 0160b430f4
commit 4a78b2dc8c
4 changed files with 66 additions and 38 deletions
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rtl837x_port.c
+1 -26
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@@ -28,8 +28,6 @@ extern __xdata struct machine_runtime machine_detected;
__xdata uint32_t l2_head;
/* Bounded-wait counter for the L2 table helpers; xdata because the 8051
* internal-RAM overlay (OSEG) is full. */
__xdata uint8_t l2mc_guard;
__xdata struct vlan_settings vlan_settings;
@@ -320,11 +318,6 @@ void vlan_setup(void) __banked
/*
* Forget the dynamic L2 entries learned on one port.
*
* Same flush engine as port_l2_forget(), but with a single-port mask so a
* topology change only ages out the affected port instead of the whole
* table. Bounded wait (cf. port_l2mc_set): this runs from the STP tick, and
* an unbounded poll on a stuck engine would freeze the main loop.
*/
void port_l2_forget_port(uint8_t port) __banked
{
@@ -429,30 +422,12 @@ void port_l2_learned(void) __banked
/*
* Static L2 multicast entry for the link-local group 01:80:C2:00:00:<mac_last>
* in VLAN `vid`, with member portmask `pmask` (bit 9 = CPU port).
*
* Slow-protocol frames (LACP, STP BPDUs) must reach the CPU without being
* flooded to other ports. The RMA "trap" action cannot deliver to the
* internal NIC on this hardware (its destination is an external CPU on a
* physical port), so the protocol modules keep the RMA action at "forward"
* and constrain the egress with this entry instead: the lookup hits the
* entry's portmask rather than the VLAN flood mask (hardware-verified with
* both the CPU bit cleared - delivery stops - and CPU-only - no egress).
*
* SMI layout (vendor SDK, L2-multicast entry variant):
* DATA_IN_A = MAC bytes 5..2 -> c2 00 00 <mac_last>
* DATA_IN_B = MAC[1..0] | vid<<16 | IVL<<29 | pmask[1:0]<<30
* DATA_IN_C = pmask[9:2]
* Lookups are IVL (a VID-0 entry is not matched), so callers add one entry
* per PVID in use. The write command (table 4 = the whole L2 LUT) hashes
* MAC+VID and picks the bucket slot itself; TBL_EXECUTE self-clears.
* Overwriting the same MAC+VID replaces the entry, so a caller can retarget
* the mask at will (e.g. back to all ports to restore flooding).
*/
void port_l2mc_set(uint8_t mac_last, __xdata uint16_t vid, __xdata uint16_t pmask) __banked
{
l2mc_guard = 0;
do { /* wait out any previous table op (bounded, cf. the IGMP guards) */
do {
reg_read_m(RTL837X_TBL_CTRL);
} while ((sfr_data[3] & TBL_EXECUTE) && ++l2mc_guard);