Milestone 1 of docs/superpowers/plans/2026-10-16-lance-ethernet.md.
Modelled:
* MAME am79c90 (AM79C90) at the firmware's two windows -- bit 0x5900000 is
RAP, 0x5800000 is RDP; every other offset in those windows still falls
through to the board model.
* the Ethernet address ROM at bit 0x6800000, as EIGHT bytes. The plan said
six; the firmware's reader (0x3FDD7520) actually loops i = 0..7 and then
validates a folded ones-complement checksum over bytes 0..5 against
bytes 6..7 (0x3FDD78B0). For the MAC 08:00:2b:16:4b:5a that is 0xC186, so
the ROM is 08 00 2b 16 4b 5a c1 86. A six-byte ROM returns expected = 0
and fails LEVEL1/2 ERROR -> ETHERNET ROM CHECKSUM - 23. The checksum
bytes are derived from the firmware's own algorithm (documented in
LANCE_REPORT.md); they are not read off a real PROM.
* the interrupt on INT1, matching the ISR 0x3FA93400 and INTENB bit 1.
* bus-master DMA, translating the LANCE's byte address to the TMS34010's
bit-addressed main RAM (byte B -> word B>>1), cross-checked against the
firmware's own CSR1 = 0xFF60 = RAM word 0x7FB0.
* VT1200_LANCELOG to trace the register/ROM accesses.
Observed with the firmware's own diagnostics menu (driven by the real LK401
model; new menu_keys.lua): the M -- ETHERNET ROM TEST now PASSES. The
C -- LANCE TEST runs the chip for real -- the firmware's init block
(mode 0x004C = LOOP|INTL|DTCR, PADR 08:00:2b:16:4b:5a) is read via the new DMA,
INIT completes (CSR0 = 0x6FE3, IDON), the chip transmits and receives -- but its
internal-loopback receive still reports a CRC error under MAME (RCV descriptor
1 = 0x4B00, message count 0). Cause: MAME's receive() runs the FCS check when
MODE_LOOP && MODE_DTCR (am79c90.cpp:263) even though DTCR means no FCS was
appended. No MAME change was made; quoted and reported in LANCE_REPORT.md.
The OS (skip gate) reads the ROM MAC, programs CSR1/2/3, INITs, sees IDON,
STRTs and polls CSR0; the Terminal Manager now shows Ethernet Address
08-00-2B-16-4B-5A (was 00-00-00-00-00-00) and LAT_08002B164B5A.
Baselines unchanged: no-env samples=198 (3 PCs), VT1200_IO_PATH_STUB samples=53
(75 PCs). ROM md5 unchanged. No MAME tree changes.
