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pureboot 7: the same features in fewer words on every chip

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Four cuts, none touching what the loader can do. The entry stub stops
re-doing the reset logic's own SP write where the datasheet guarantees
RAMEND (stack::hardware — the classic megas keep theirs). The autobaud
unit moves into GPIOR2:GPIOR1 wherever the chip has the pair: one-word
accesses, no RAM object, and the host's measured-clock peek follows it
by version and geometry. 'J' rides the unified decode, carrying a
selector it ignores so its address is the same two reads as every other
command — the tool sends the bare form to older residents. run_app stops
insisting on a body of its own. The fleet lands at 358–410 B stock and
438–474 B autobaud; the tightest image in the space — the 1284s'
autobaud on a USART's own pins with the OSCCAL trim — drops from 510 to
484 of its 512. Every chip's suite is green on the wire that changed,
and the README's table is machine-checked against the built images.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
BlackMark
2026-07-28 17:02:38 +02:00
parent a3ea099105
commit 8f6319c068
9 changed files with 164 additions and 103 deletions
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102
pureboot/pureboot.py
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@@ -26,7 +26,7 @@ else:
import termios
PROMPT = b"+"
VERSION = 6 # this tool's own version — free to drift from a loader's
VERSION = 7 # this tool's own version — free to drift from a loader's
# The loader versions this tool can drive. A pureboot version implies its wire
# protocol, which carries no number of its own, so this window is where that
# map lives: the tool keeps a decoder for every generation in it (1–4 speak
@@ -34,7 +34,7 @@ VERSION = 6 # this tool's own version — free to drift from a loader's
# builds and changes nothing on the wire), and a version it has no decoder
# for moves the floor.
OLDEST_LOADER = 1
NEWEST_LOADER = 6
NEWEST_LOADER = 7
SLOT = 512 # the loader slot, on every chip
RETRIES = 3 # rewrites of a page that reads back wrong, before the run stops
@@ -45,11 +45,13 @@ RETRIES = 3 # rewrites of a page that reads back wrong, before the run stops
UNIFIED_LOADER = 5
SP_FLASH, SP_EEPROM, SP_RAM, SP_FUSE, SP_SPM = 0, 1, 2, 3, 4
# A v5+ autobaud loader keeps its measured bit period at ram_start, encoded
# as delay-loop counts: (bit cycles − UNIT_DISCOUNT) / UNIT_LOOP_CYCLES,
# An autobaud loader keeps its measured bit period readable, encoded as
# delay-loop counts: (bit cycles − UNIT_DISCOUNT) / UNIT_LOOP_CYCLES,
# floored — the spin granule and per-bit overhead of libavr's software UART.
# --info undoes the encoding to report the true clock, which therefore sits
# within one granule below it.
# v5/v6 keep it at ram_start; v7 moves it into GPIOR2:GPIOR1 on the chips
# that have the pair (their data addresses are in the geometry) and keeps
# ram_start only where they do not exist. --info undoes the encoding to
# report the true clock, which therefore sits within one granule below it.
UNIT_LOOP_CYCLES, UNIT_DISCOUNT = 4, 8
# A selector's high nibble is the flash bank — the address bits above the 16-bit
@@ -77,36 +79,40 @@ CALIBRATE = 0xC0
# from its chip database at build time). Die revisions that share a signature
# share this row, as they share the silicon.
CHIP_GEOMETRY = {
# signature : (flash, page, eeprom, patch_vector, ram_start)
# signature : (flash, page, eeprom, patch_vector, ram_start, gpior1)
# ram_start is where SRAM begins in data space: the classic megas and the
# tinies keep it right after the plain I/O registers (0x60), the x8/x4
# generations past their extended I/O file (0x100). An autobaud loader's
# measured bit period lives at exactly ram_start (its only RAM object;
# the loader's own build pins the layout), which is what --info reads.
(0x1E, 0x90, 0x07): (1024, 32, 64, True, 0x60), # ATtiny13/13A
(0x1E, 0x91, 0x08): (2048, 32, 128, True, 0x60), # ATtiny25
(0x1E, 0x92, 0x06): (4096, 64, 256, True, 0x60), # ATtiny45
(0x1E, 0x93, 0x0B): (8192, 64, 512, True, 0x60), # ATtiny85
(0x1E, 0x92, 0x05): (4096, 64, 256, True, 0x100), # ATmega48/48A
(0x1E, 0x92, 0x0A): (4096, 64, 256, True, 0x100), # ATmega48P/48PA
(0x1E, 0x93, 0x07): (8192, 64, 512, False, 0x60), # ATmega8/8A
(0x1E, 0x93, 0x0A): (8192, 64, 512, False, 0x100), # ATmega88/88A
(0x1E, 0x93, 0x0F): (8192, 64, 512, False, 0x100), # ATmega88P/88PA
(0x1E, 0x94, 0x03): (16384, 128, 512, False, 0x60), # ATmega16/16A
(0x1E, 0x94, 0x06): (16384, 128, 512, False, 0x100), # ATmega168/168A
(0x1E, 0x94, 0x0B): (16384, 128, 512, False, 0x100), # ATmega168P/168PA
(0x1E, 0x94, 0x0A): (16384, 128, 512, False, 0x100), # ATmega164P/164PA
(0x1E, 0x94, 0x0F): (16384, 128, 512, False, 0x100), # ATmega164A
(0x1E, 0x95, 0x02): (32768, 128, 1024, False, 0x60), # ATmega32/32A
(0x1E, 0x95, 0x0F): (32768, 128, 1024, False, 0x100), # ATmega328P
(0x1E, 0x95, 0x14): (32768, 128, 1024, False, 0x100), # ATmega328
(0x1E, 0x95, 0x08): (32768, 128, 1024, False, 0x100), # ATmega324P
(0x1E, 0x95, 0x11): (32768, 128, 1024, False, 0x100), # ATmega324PA
(0x1E, 0x95, 0x15): (32768, 128, 1024, False, 0x100), # ATmega324A
(0x1E, 0x96, 0x09): (65536, 256, 2048, False, 0x100), # ATmega644/644A
(0x1E, 0x96, 0x0A): (65536, 256, 2048, False, 0x100), # ATmega644P/644PA
(0x1E, 0x97, 0x05): (131072, 256, 4096, False, 0x100),# ATmega1284P
(0x1E, 0x97, 0x06): (131072, 256, 4096, False, 0x100),# ATmega1284
# generations past their extended I/O file (0x100). gpior1 is GPIOR1's
# data address — 0x32 on the t25/45/85, 0x4A from the x8 generation on,
# None where the chip has no pair (t13, classic megas). A v7 autobaud
# loader's measured bit period lives in GPIOR2:GPIOR1 where they exist
# and at exactly ram_start elsewhere (its only RAM object; the loader's
# own build pins the layout); v5/v6 always used ram_start. --info reads
# whichever home the answering version implies.
(0x1E, 0x90, 0x07): (1024, 32, 64, True, 0x60, None), # ATtiny13/13A
(0x1E, 0x91, 0x08): (2048, 32, 128, True, 0x60, 0x32), # ATtiny25
(0x1E, 0x92, 0x06): (4096, 64, 256, True, 0x60, 0x32), # ATtiny45
(0x1E, 0x93, 0x0B): (8192, 64, 512, True, 0x60, 0x32), # ATtiny85
(0x1E, 0x92, 0x05): (4096, 64, 256, True, 0x100, 0x4A), # ATmega48/48A
(0x1E, 0x92, 0x0A): (4096, 64, 256, True, 0x100, 0x4A), # ATmega48P/48PA
(0x1E, 0x93, 0x07): (8192, 64, 512, False, 0x60, None), # ATmega8/8A
(0x1E, 0x93, 0x0A): (8192, 64, 512, False, 0x100, 0x4A), # ATmega88/88A
(0x1E, 0x93, 0x0F): (8192, 64, 512, False, 0x100, 0x4A), # ATmega88P/88PA
(0x1E, 0x94, 0x03): (16384, 128, 512, False, 0x60, None), # ATmega16/16A
(0x1E, 0x94, 0x06): (16384, 128, 512, False, 0x100, 0x4A), # ATmega168/168A
(0x1E, 0x94, 0x0B): (16384, 128, 512, False, 0x100, 0x4A), # ATmega168P/168PA
(0x1E, 0x94, 0x0A): (16384, 128, 512, False, 0x100, 0x4A), # ATmega164P/164PA
(0x1E, 0x94, 0x0F): (16384, 128, 512, False, 0x100, 0x4A), # ATmega164A
(0x1E, 0x95, 0x02): (32768, 128, 1024, False, 0x60, None), # ATmega32/32A
(0x1E, 0x95, 0x0F): (32768, 128, 1024, False, 0x100, 0x4A), # ATmega328P
(0x1E, 0x95, 0x14): (32768, 128, 1024, False, 0x100, 0x4A), # ATmega328
(0x1E, 0x95, 0x08): (32768, 128, 1024, False, 0x100, 0x4A), # ATmega324P
(0x1E, 0x95, 0x11): (32768, 128, 1024, False, 0x100, 0x4A), # ATmega324PA
(0x1E, 0x95, 0x15): (32768, 128, 1024, False, 0x100, 0x4A), # ATmega324A
(0x1E, 0x96, 0x09): (65536, 256, 2048, False, 0x100, 0x4A), # ATmega644/644A
(0x1E, 0x96, 0x0A): (65536, 256, 2048, False, 0x100, 0x4A), # ATmega644P/644PA
(0x1E, 0x97, 0x05): (131072, 256, 4096, False, 0x100, 0x4A),# ATmega1284P
(0x1E, 0x97, 0x06): (131072, 256, 4096, False, 0x100, 0x4A),# ATmega1284
}
VERBOSE = False
@@ -450,7 +456,7 @@ class Info:
if geometry is None:
sig = " ".join(f"{b:02x}" for b in signature)
raise Error(f"unknown signature {sig} — this tool has no geometry for it")
flash, page, eeprom, patch, _ = geometry
flash, page, eeprom, patch, _, _ = geometry
base = flash - SLOT
word_flash = flash > 0x10000
wire_base = base // 2 if word_flash else base
@@ -491,6 +497,11 @@ class Info:
# permits where from_identity refuses.
geometry = CHIP_GEOMETRY.get(tuple(self.signature))
self.ram = geometry[4] if geometry else None
# Where this loader keeps the measured bit period (None when a fixed
# signature row is missing): the GPIOR pair from v7 where the chip
# has one, ram_start before that and everywhere without the pair.
gpior1 = geometry[5] if geometry else None
self.unit_home = gpior1 if self.version >= 7 and gpior1 is not None else self.ram
def describe(self):
sig = " ".join(f"{b:02x}" for b in self.signature)
@@ -745,8 +756,13 @@ class Loader:
return self._command(b"F", 4, 2.0)
def jump(self, word_address):
"""The device acks, then execution continues at the word address."""
self.port.write(bytes((ord("J"), word_address & 0xFF, word_address >> 8)))
"""The device acks, then execution continues at the word address.
From v7 'J' rides the unified decode, so it carries a selector byte
the loader ignores; older loaders take the bare address."""
if self.info.version >= 7:
self.port.write(bytes((ord("J"), 0, word_address & 0xFF, word_address >> 8)))
else:
self.port.write(bytes((ord("J"), word_address & 0xFF, word_address >> 8)))
self._expect_prompt()
def enter_copy(self, byte_address, wait, link=None):
@@ -1541,14 +1557,14 @@ def main():
print("device:")
for line in info.lines():
print(f" {line}")
if args.autobaud and info.ram is not None:
# The whole of the loader's RAM is the measured bit period at
# ram_start; decoded and times the rate this session drives,
if args.autobaud and info.unit_home is not None:
# The measured bit period, from wherever this version keeps it
# (unit_home); decoded and times the rate this session drives,
# that is the true clock — the number to hold an OSCCAL bake
# or a fixed-baud build against (README.md: deployment). The
# autobaud identity path refuses unknown signatures, so ram is
# always known here; the guard states that dependency.
unit = int.from_bytes(loader.read_ram(info.ram, 2), "little")
# autobaud identity path refuses unknown signatures, so the
# home is always known here; the guard states that dependency.
unit = int.from_bytes(loader.read_ram(info.unit_home, 2), "little")
cycles = unit * UNIT_LOOP_CYCLES + UNIT_DISCOUNT
clock = cycles * args.baud
offset = f", {(clock / args.clock - 1) * 100:+.1f} % of {args.clock}" if args.clock else ""