FA-89826 / Instruction set emulation / Open access

16 KiB ROM not mirrored into the upper window · case 01

Reads from 0xC000 upward return bytes past the end of a 16 KiB ROM.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

ROM offsets are not reduced modulo the ROM size.

VERIFIED REPAIR

Reduce the ROM offset modulo rom_size.

Unsuccessful approach: Always mirroring at 16 KiB breaks 32 KiB ROMs.

Case contract

Input [rom_size, sram_enabled, ops] with ops ['r', addr] or ['w', addr, value] on a 16-bit bus. 0x0000-0x1FFF: 2 KiB RAM mirrored every 0x800. 0x2000-0x3FFF: 8 video registers mirrored every 8 bytes. 0x4000-0x4017: I/O registers. 0x4018-0x5FFF: unmapped. 0x6000-0x7FFF: SRAM when enabled, else unmapped. 0x8000-0xFFFF: ROM of rom_size bytes mirrored to fill the window, byte at offset o = (7o + (o >> 8) + 3) & 0xFF, writes ignored. Every write drives its value onto the data bus; reads of unmapped space return the last bus value, other reads drive the bus. Unwritten RAM/register/SRAM bytes read 0. Writes yield None, reads the value.

Why this case matters

Console and microcontroller emulators depend on exact address decoding; mirroring and open-bus behaviour are relied on by real software.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    rom_size, sram_en, ops = args
    ram, ppu, io, sram = {}, {}, {}, {}
    bus = 0
    out = []
    for op in ops:
        kind, addr = op[0], op[1] & 0xFFFF
        if addr < 0x2000: dev, key = ram, addr & 0x7FF
        elif addr < 0x4000: dev, key = ppu, addr & 7
        elif addr < 0x4018: dev, key = io, addr
        elif addr < 0x6000: dev, key = None, None
        elif addr < 0x8000: dev, key = (sram, addr - 0x6000) if sram_en else (None, None)
        else: dev, key = 'rom', (addr - 0x8000) & 0x7FFF
        if kind == 'w':
            bus = op[2] & 0xFF
            if dev is not None and dev != 'rom':
                dev[key] = bus
            out.append(None)
        else:
            if dev == 'rom': bus = (key * 7 + (key >> 8) + 3) & 0xFF
            elif dev is not None: bus = dev.get(key, 0)
            out.append(bus)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('ram mirrors', [32768, 1, [['w', 2049, 67], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 67, 67, 67]), ('video register mirrors', [32768, 1, [['w', 8201, 5], ['r', 16377], ['r', 8193]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 17], ['r', 16640]]], [None, 119, None, 17]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17665]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49158], ['r', 32774]]], [45, 45]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49158]]], [102, None, 109]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 152], ['r', 24576], ['r', 24577]]], [None, 152, 152]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 68], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 68, 68, 68]), ('video register mirrors', [32768, 1, [['w', 8202, 5], ['r', 16378], ['r', 8194]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 18], ['r', 16640]]], [None, 119, None, 18]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17666]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49159], ['r', 32775]]], [52, 52]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49159]]], [102, None, 116]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 151], ['r', 24576], ['r', 24577]]], [None, 151, 151]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 69], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 69, 69, 69]), ('video register mirrors', [32768, 1, [['w', 8203, 5], ['r', 16379], ['r', 8195]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 19], ['r', 16640]]], [None, 119, None, 19]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17667]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49160], ['r', 32776]]], [59, 59]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49160]]], [102, None, 123]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 150], ['r', 24576], ['r', 24577]]], [None, 150, 150]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 70], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 70, 70, 70]), ('video register mirrors', [32768, 1, [['w', 8204, 5], ['r', 16380], ['r', 8196]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 20], ['r', 16640]]], [None, 119, None, 20]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17668]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49161], ['r', 32777]]], [66, 66]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49161]]], [102, None, 130]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 149], ['r', 24576], ['r', 24577]]], [None, 149, 149]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 71], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 71, 71, 71]), ('video register mirrors', [32768, 1, [['w', 8205, 5], ['r', 16381], ['r', 8197]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 21], ['r', 16640]]], [None, 119, None, 21]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17669]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49162], ['r', 32778]]], [73, 73]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49162]]], [102, None, 137]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 148], ['r', 24576], ['r', 24577]]], [None, 148, 148]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
ram mirrors	`[None, 67, 67, 67]`	`[None, 67, 67, 67]`	Passed
video register mirrors	`[None, 5, 5]`	`[None, 5, 5]`	Passed
open bus after unmapped write	`[None, 119, None, 17]`	`[None, 119, None, 17]`	Passed
open bus after read	`[24, 24]`	`[24, 24]`	Passed
small rom mirrors	`[109, 45]`	`[45, 45]`	Failed
large rom does not mirror	`[102, None, 109]`	`[102, None, 109]`	Passed
io registers	`[None, 15, 0]`	`[None, 15, 0]`	Passed
disabled sram is open bus	`[None, 152, 152]`	`[None, 152, 152]`	Passed
enabled sram	`[None, 18, 0]`	`[None, 18, 0]`	Passed

SHA-256 / f67b279c51a8f1b1f1161ae949e4295582b45aaeddc511a7859763df2778b75a

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    rom_size, sram_en, ops = args
    ram, ppu, io, sram = {}, {}, {}, {}
    bus = 0
    out = []
    for op in ops:
        kind, addr = op[0], op[1] & 0xFFFF
        if addr < 0x2000: dev, key = ram, addr & 0x7FF
        elif addr < 0x4000: dev, key = ppu, addr & 7
        elif addr < 0x4018: dev, key = io, addr
        elif addr < 0x6000: dev, key = None, None
        elif addr < 0x8000: dev, key = (sram, addr - 0x6000) if sram_en else (None, None)
        else: dev, key = 'rom', (addr - 0x8000) % 0x4000
        if kind == 'w':
            bus = op[2] & 0xFF
            if dev is not None and dev != 'rom':
                dev[key] = bus
            out.append(None)
        else:
            if dev == 'rom': bus = (key * 7 + (key >> 8) + 3) & 0xFF
            elif dev is not None: bus = dev.get(key, 0)
            out.append(bus)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('ram mirrors', [32768, 1, [['w', 2049, 67], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 67, 67, 67]), ('video register mirrors', [32768, 1, [['w', 8201, 5], ['r', 16377], ['r', 8193]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 17], ['r', 16640]]], [None, 119, None, 17]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17665]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49158], ['r', 32774]]], [45, 45]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49158]]], [102, None, 109]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 152], ['r', 24576], ['r', 24577]]], [None, 152, 152]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 68], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 68, 68, 68]), ('video register mirrors', [32768, 1, [['w', 8202, 5], ['r', 16378], ['r', 8194]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 18], ['r', 16640]]], [None, 119, None, 18]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17666]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49159], ['r', 32775]]], [52, 52]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49159]]], [102, None, 116]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 151], ['r', 24576], ['r', 24577]]], [None, 151, 151]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 69], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 69, 69, 69]), ('video register mirrors', [32768, 1, [['w', 8203, 5], ['r', 16379], ['r', 8195]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 19], ['r', 16640]]], [None, 119, None, 19]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17667]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49160], ['r', 32776]]], [59, 59]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49160]]], [102, None, 123]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 150], ['r', 24576], ['r', 24577]]], [None, 150, 150]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 70], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 70, 70, 70]), ('video register mirrors', [32768, 1, [['w', 8204, 5], ['r', 16380], ['r', 8196]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 20], ['r', 16640]]], [None, 119, None, 20]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17668]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49161], ['r', 32777]]], [66, 66]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49161]]], [102, None, 130]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 149], ['r', 24576], ['r', 24577]]], [None, 149, 149]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 71], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 71, 71, 71]), ('video register mirrors', [32768, 1, [['w', 8205, 5], ['r', 16381], ['r', 8197]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 21], ['r', 16640]]], [None, 119, None, 21]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17669]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49162], ['r', 32778]]], [73, 73]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49162]]], [102, None, 137]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 148], ['r', 24576], ['r', 24577]]], [None, 148, 148]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
ram mirrors	`[None, 67, 67, 67]`	`[None, 67, 67, 67]`	Passed
video register mirrors	`[None, 5, 5]`	`[None, 5, 5]`	Passed
open bus after unmapped write	`[None, 119, None, 17]`	`[None, 119, None, 17]`	Passed
open bus after read	`[24, 24]`	`[24, 24]`	Passed
small rom mirrors	`[45, 45]`	`[45, 45]`	Passed
large rom does not mirror	`[38, None, 45]`	`[102, None, 109]`	Failed
io registers	`[None, 15, 0]`	`[None, 15, 0]`	Passed
disabled sram is open bus	`[None, 152, 152]`	`[None, 152, 152]`	Passed
enabled sram	`[None, 18, 0]`	`[None, 18, 0]`	Passed

SHA-256 / c52fb813e5a574abea4b9e2204bf70c390357c5667f139dce3ecdf1280f6e7c0

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    rom_size, sram_en, ops = args
    ram, ppu, io, sram = {}, {}, {}, {}
    bus = 0
    out = []
    for op in ops:
        kind, addr = op[0], op[1] & 0xFFFF
        if addr < 0x2000: dev, key = ram, addr & 0x7FF
        elif addr < 0x4000: dev, key = ppu, addr & 7
        elif addr < 0x4018: dev, key = io, addr
        elif addr < 0x6000: dev, key = None, None
        elif addr < 0x8000: dev, key = (sram, addr - 0x6000) if sram_en else (None, None)
        else: dev, key = 'rom', (addr - 0x8000) % rom_size
        if kind == 'w':
            bus = op[2] & 0xFF
            if dev is not None and dev != 'rom':
                dev[key] = bus
            out.append(None)
        else:
            if dev == 'rom': bus = (key * 7 + (key >> 8) + 3) & 0xFF
            elif dev is not None: bus = dev.get(key, 0)
            out.append(bus)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('ram mirrors', [32768, 1, [['w', 2049, 67], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 67, 67, 67]), ('video register mirrors', [32768, 1, [['w', 8201, 5], ['r', 16377], ['r', 8193]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 17], ['r', 16640]]], [None, 119, None, 17]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17665]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49158], ['r', 32774]]], [45, 45]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49158]]], [102, None, 109]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 152], ['r', 24576], ['r', 24577]]], [None, 152, 152]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 68], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 68, 68, 68]), ('video register mirrors', [32768, 1, [['w', 8202, 5], ['r', 16378], ['r', 8194]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 18], ['r', 16640]]], [None, 119, None, 18]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17666]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49159], ['r', 32775]]], [52, 52]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49159]]], [102, None, 116]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 151], ['r', 24576], ['r', 24577]]], [None, 151, 151]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 69], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 69, 69, 69]), ('video register mirrors', [32768, 1, [['w', 8203, 5], ['r', 16379], ['r', 8195]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 19], ['r', 16640]]], [None, 119, None, 19]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17667]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49160], ['r', 32776]]], [59, 59]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49160]]], [102, None, 123]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 150], ['r', 24576], ['r', 24577]]], [None, 150, 150]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 70], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 70, 70, 70]), ('video register mirrors', [32768, 1, [['w', 8204, 5], ['r', 16380], ['r', 8196]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 20], ['r', 16640]]], [None, 119, None, 20]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17668]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49161], ['r', 32777]]], [66, 66]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49161]]], [102, None, 130]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 149], ['r', 24576], ['r', 24577]]], [None, 149, 149]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])], [('ram mirrors', [32768, 1, [['w', 2049, 71], ['r', 1], ['r', 6145], ['r', 4097]]], [None, 71, 71, 71]), ('video register mirrors', [32768, 1, [['w', 8205, 5], ['r', 16381], ['r', 8197]]], [None, 5, 5]), ('open bus after unmapped write', [32768, 1, [['w', 16416, 119], ['r', 20480], ['w', 2, 21], ['r', 16640]]], [None, 119, None, 21]), ('open bus after read', [32768, 1, [['r', 32771], ['r', 17669]]], [24, 24]), ('small rom mirrors', [16384, 1, [['r', 49162], ['r', 32778]]], [73, 73]), ('large rom does not mirror', [32768, 0, [['r', 49157], ['w', 49157, 1], ['r', 49162]]], [102, None, 137]), ('io registers', [32768, 1, [['w', 16405, 15], ['r', 16405], ['r', 16406]]], [None, 15, 0]), ('disabled sram is open bus', [32768, 0, [['w', 28672, 148], ['r', 24576], ['r', 24577]]], [None, 148, 148]), ('enabled sram', [16384, 1, [['w', 28672, 18], ['r', 28672], ['r', 24576]]], [None, 18, 0])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
ram mirrors	`[None, 67, 67, 67]`	`[None, 67, 67, 67]`	Passed
video register mirrors	`[None, 5, 5]`	`[None, 5, 5]`	Passed
open bus after unmapped write	`[None, 119, None, 17]`	`[None, 119, None, 17]`	Passed
open bus after read	`[24, 24]`	`[24, 24]`	Passed
small rom mirrors	`[45, 45]`	`[45, 45]`	Passed
large rom does not mirror	`[102, None, 109]`	`[102, None, 109]`	Passed
io registers	`[None, 15, 0]`	`[None, 15, 0]`	Passed
disabled sram is open bus	`[None, 152, 152]`	`[None, 152, 152]`	Passed
enabled sram	`[None, 18, 0]`	`[None, 18, 0]`	Passed

SHA-256 / 98b37d79126d3d78dc9ebed31b78a8e59b914727c242ce8373bd47a2f4d8a516

Verification & scope

A deterministic bounded teaching model of one emulator rule; the instruction semantics are a stipulated contract inspired by common ISAs and are not a claim of cycle-exact or architectural conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:21.101061+00:00.

Case digest / 4bd656375354d4bd5f84fba90d245b90186bcca49a54bd2c7f908ab584239617