The far machinery (ELPM reads, RAMPZ page commands, wire-word math)
costs ~46 B over the m328P's 504, and the tsb-calibrated C++-to-asm
gap says no implementation of this feature set reaches 512 on this
chip — a boundary its hardware does not have anyway: the 1284P's
smallest boot sector is 1 KiB. The slot therefore becomes
per-geometry (512 B, or 1 KiB past 64 KiB), which the host derives
from the word-addressing flag; slot arithmetic unifies (the index is
the wire high byte with its low bit dropped in either unit), the
update preflight demands a two-slot boot section in the chip's own
terms, and pbapp's hand-back jumps to the real slot base. libavr's
far primitives split their RAMPZ/Z asm operands (a page never
crosses 64 KiB, so callers keep a byte and a 16-bit cursor — the
32-bit address folds away; flash_load_far's byte form becomes the
out-RAMPZ+elpm pair avr-libc's pgm_read_byte_far rebuilds per call),
and the host splits reads at 64 KiB boundaries. All ten chips pass
the full suite — the 1284P at 558 B including protocol, relocation,
and the power-fail self-update — with pureboot byte-identical across
generated and reflect modes everywhere, and the original three
chips' images unchanged to the byte (488/502/504).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
check_pi.py asserts the two link-time facts position independence rests on
(no absolute jmp/call; the info block within the image's first 256 bytes);
the size gates drop to 510 on the tinies for the trampoline word.
New per-chip tests beside the reworked protocol test: the planner units
(programming orders and their recovery properties, the surgery, staging
composition, boot-fuse decode, and the update preflight's error/warning
matrix over synthetic fuse bytes), the relocated-copy sweep (the identical
image installed one slot lower serves the full command set — the PI
acceptance test, and the one that caught the temporary-buffer trap), and
the self-update end-to-end: --update-loader to a re-timed build
(pureboot9, byte-different by PUREBOOT_TIMEOUT alone), then every
power-fail phase killed mid-write, restarted from the runner's flash dump,
and completed by a re-run with the application intact throughout. The mega
rounds run the BOOTRST-unprogrammed profile: the fixture application's 'L'
jump is the application-owned loader entry that profile relies on.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
