Changes from ANFS 4.21 (variant 1) to ANFS 4.24

ANFS 4.24 is the next Master 128 ANFS after 4.21 (variant 1). Both are 65C02 ROMs that keep their filing-system workspace in HAZEL hidden RAM at &C000–&C2FF, so 4.24 inherits the whole Master-128 architecture 4.21 introduced. The two 16 KB ROMs share 93.9 % of their opcode structure; the byte-level similarity is 85.1 %, and only 2.3 % of bytes match at the same offset because almost every operand shifted as code grew and moved.

The differences are refinements rather than a redesign: a scattering of defensive fixes and a handful of routines compacted or reshaped. None changes externally-visible behaviour.

ROM header

The service entry moves down by &36 bytes, tracking the code inserted ahead of it.

Defensive CLD guards in the interrupt paths

4.24 adds four CLD instructions at the head of paths reachable from Econet NMI / IRQ context:

An interrupt can arrive while the foreground has the decimal flag set; each guard clears D so the binary ADC / SBC further down its path computes correctly. 4.21 relied on callers never leaving D set. A fifth CLD byte sits at &8397 but is unreached (it follows an RTS), so it is inert.

ACCCON-guarded buffer stores

The Master 128 reaches the Econet receive buffer through shadow / HAZEL paging, controlled by ACCCON. 4.24 widens the save-restore of ACCCON around the buffer writes. The clearest new instance is the last-data-byte store at &8284: it saves ACCCON, switches to the caller's paging value in escapable, performs the (open_port_buf),Y store, then restores ACCCON — so the write lands in the correct RAM regardless of what the interrupted foreground had paged in.

Credits easter egg rewritten

The * credits keyword handler drops its hand-written character-emit loop. Where 4.21 walked credits_keyword_start byte by byte through OSASCI, 4.24 emits the same text with a single jsr print_inline (at &8D59) over the inline, high-bit-terminated string at &8D5C. The &EA (NOP) terminator doubles as the resume opcode and falls through to the RTS. The string still lists the four authors (B Cockburn, J Dunn, B Robertson, J Wills).

print_fs_address / print_ps_address share one tail

4.21 had two near-identical routines that each read a network.station pair from CMOS and printed it. 4.24 folds them into one body: print_ps_address loads X=4 and branches into the shared tail; print_fs_address loads X=2 and falls straight in. The shared tail print_cmos_pair prints CMOS[X], a ., then CMOS[X-1], deriving the station index with PHX / PLX / DEX instead of a second literal LDX.

Immediate-operation handlers compacted

The port-0 immediate-operation setup block (&848B–&84F9 in 4.21) is reshaped: the dispatch low-byte table moves, and the machine-type handler at &84C7 now uses the same workspace-offset setup as the PEEK path (port_ws_offset = &2E, rx_buf_offset = &0D, then jsr tx_calc_transfer) rather than writing its own buffer dimensions.

The transfer-size routine tx_calc_transfer is relocated from &8900 to &85AD (its three call sites move with it) and gains a CLD guard and a new shadow-RAM branch: when the buffer is a Tube address and ACCCON.E marks shadow RAM enabled, it now sets the shadow bit in escapable before the 4-byte size subtraction.

New command sub-table record

4.24 inserts a five-byte record — 4F 6E 80 00 00, ASCII "On" followed by table markers — into the FS-command sub-table at &A80E, immediately after that sub-table's shifted default-handler word (&8E44, i.e. &8E45-1, the *command / *RUN-& classifier). This is the one net-new record in the command tables; it is why command-table addresses shift by +&14 before it and +&19 after. (The preceding word &8E2C→&8E44 is not new — it is the same default-handler slot, shifted with the extended- vector region.)

TX control block grows a byte

Several TXCB field offsets shift by +1 (e.g. the destination-offset load LDY #&2C→LDY #&2D and the control-byte LDA #&21→LDA #&22), reflecting a one-byte growth in the transmit control block layout.

Dispatch-table bases

Every PHA/PHA/RTS dispatch table shifts with the code around it: