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pureboot: the classic megas and the word-addressed 1284P groundwork

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Device: boot-section detection probes SPMCR beside SPMCSR, the link
picks any hardware USART through the instance-aware lookups (URSEL
chips included), WDRF reads MCUSR-or-MCUCSR, and the >64 KiB shape
lands — word-addressed wire flash (info flag bit 1, page byte 0 means
256, base as a word address), far reads through flash_load_far, a
single 32-bit byte-cursor page walk (the 256-byte page wraps its low
byte exactly), and slot arithmetic in words (the return address
already is one). Host: addresses stay bytes internally and scale at
the wire, the boot-fuse decode becomes a per-signature table (byte
index + BOOTSZ ladder — the m168A's lives in EXTENDED), and the
planner tests pin every chip's ladder plus the word-addressed info
decode. Tests: the device runner serves every mega over the USART pty,
pbapp banners over the right link, the update rehearsal synthesizes
its assumed fuses from the tool's own table, and the PI lint tracks
the renamed info symbol. All six classic-mega/168A targets pass the
full suite (size, PI, planner, protocol, reloc, self-update) at
466–504 B; the 1284P builds await a libavr far-path slimming to make
its 512.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
BlackMark
2026-07-21 12:00:19 +02:00
parent a1ff032c87
commit 0fa53e1cad
12 changed files with 755 additions and 126 deletions
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18
test/pbupdate.py
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@@ -41,7 +41,17 @@ class PowerFail(Exception):
pass
MEGA_FUSES = "ffffffdd" # high 0xdd: BOOTSZ = 1 KB, BOOTRST unprogrammed
def assumed_fuses(pb, image):
"""Synthetic 'F' bytes for --assume-fuses: the smallest boot section of
at least 1 KB (what a self-update needs), BOOTRST unprogrammed — the
per-chip BOOTSZ ladder and fuse byte come from the tool's own table,
keyed by the update image's embedded signature."""
info = pb.image_info(image)
which, ladder = pb.BOOT_FUSE[bytes(info.signature[1:3])]
bits = min((b for b in ladder if ladder[b] * 2 >= 1024), key=lambda b: ladder[b])
fuses = bytearray((0xFF, 0xFF, 0xFF, 0xFF))
fuses[which] = 0xF8 | (bits << 1) | 1
return bytes(fuses)
def make_fault_loader(pb, base, kill_region, kill_hits, device):
@@ -77,7 +87,7 @@ def make_fault_loader(pb, base, kill_region, kill_hits, device):
def main():
(device_bin, elf, update_elf, mcu, hz, base_hex, page, baud, app_bin, tool, workdir) = sys.argv[1:]
base, page, baud = int(base_hex, 0), int(page), int(baud)
mega = mcu == "atmega328p"
mega = mcu.startswith("atmega")
reset_hex = "0" if mega else None # the mega runs BOOTRST-unprogrammed here
sys.path.insert(0, os.path.dirname(os.path.abspath(tool)))
sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
@@ -95,7 +105,7 @@ def main():
fail("the update image is byte-identical to the resident build")
dump = os.path.join(workdir, "dump.bin")
state = os.path.join(workdir, "update.pbstate")
fuses = bytes.fromhex(MEGA_FUSES) if mega else None
fuses = assumed_fuses(pb, images["v0"]) if mega else None
def connect(device):
port = pb.Port(device.pty, baud)
@@ -136,7 +146,7 @@ def main():
# A clean CLI update, resident -> v9.
args = ["--update-loader", os.path.join(workdir, "v9.bin"), "--state", state, "--stay"]
if mega:
args += ["--assume-fuses", MEGA_FUSES]
args += ["--assume-fuses", fuses.hex()]
out = pbsim.run_tool(tool, device.pty, baud, *args)
if "loader updated" not in out:
fail("update did not report success")