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pureboot: the activation countdown in the narrowest type that holds it

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The fixed-baud window counted down a uint32 where almost every window fits
24 bits; the countdown now takes avr::uint24_t when the poll budget allows
(the autobaud budget's own choice), uint32 past 16.7M polls — four bytes
off every fixed-baud image on every chip, the full suites green on the
changed window. The README size table is refreshed — its autobaud column
had also gone stale by the no-assembly pass's measurement-loop win, which
nothing gated: sizes.py check-readme now runs as the gate's final stage,
where every tree is freshly built and the table can actually be held.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
BlackMark
2026-07-28 14:47:29 +02:00
parent 321ff8a4ee
commit c535c4756c
4 changed files with 29 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
ide/README.md
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@@ -2,7 +2,7 @@
`master` carries `bootloader.atsln`, so this branch does too: `ide/bootloader.atsln` `master` carries `bootloader.atsln`, so this branch does too: `ide/bootloader.atsln`
builds the loaders from the same sources Ninja does, to a **byte-identical builds the loaders from the same sources Ninja does, to a **byte-identical
`.text`** — 404 B for the 328P pureboot loader, 510 B for the `tsb_asm` tier in `.text`** — 400 B for the 328P pureboot loader, 510 B for the `tsb_asm` tier in
its 512-byte section. CMake remains the build system; the solution is here so the its 512-byte section. CMake remains the build system; the solution is here so the
port opens in Studio as its predecessor did. port opens in Studio as its predecessor did.

32
pureboot/README.md
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@@ -28,21 +28,21 @@ it carries the calibration machinery and no clock at all.
| Chip | Flash | Loader at | Link | Stock | Autobaud | | Chip | Flash | Loader at | Link | Stock | Autobaud |
|---|---|---|---|---|---| |---|---|---|---|---|---|
| ATtiny13, ATtiny13A † | 1 KiB | 0x0200 | software | 394 B | 464 B | | ATtiny13, ATtiny13A † | 1 KiB | 0x0200 | software | 390 B | 460 B |
| ATtiny25 † | 2 KiB | 0x0600 | software | 398 B | 468 B | | ATtiny25 † | 2 KiB | 0x0600 | software | 394 B | 464 B |
| ATtiny45 † | 4 KiB | 0x0e00 | software | 402 B | 472 B | | ATtiny45 † | 4 KiB | 0x0e00 | software | 398 B | 468 B |
| ATtiny85 † | 8 KiB | 0x1e00 | software | 402 B | 472 B | | ATtiny85 † | 8 KiB | 0x1e00 | software | 398 B | 468 B |
| ATmega8, 8A | 8 KiB | 0x1e00 | USART0 | 364 B | 478 B | | ATmega8, 8A | 8 KiB | 0x1e00 | USART0 | 360 B | 474 B |
| ATmega16, 16A | 16 KiB | 0x3e00 | USART0 | 366 B | 482 B | | ATmega16, 16A | 16 KiB | 0x3e00 | USART0 | 362 B | 480 B |
| ATmega32, 32A | 32 KiB | 0x7e00 | USART0 | 366 B | 482 B | | ATmega32, 32A | 32 KiB | 0x7e00 | USART0 | 362 B | 480 B |
| ATmega48, 48A, 48P, 48PA † | 4 KiB | 0x0e00 | USART0 | 392 B | 468 B | | ATmega48, 48A, 48P, 48PA † | 4 KiB | 0x0e00 | USART0 | 388 B | 464 B |
| ATmega88, 88A, 88P, 88PA | 8 KiB | 0x1e00 | USART0 | 402 B | 478 B | | ATmega88, 88A, 88P, 88PA | 8 KiB | 0x1e00 | USART0 | 398 B | 474 B |
| ATmega168, 168A, 168P, 168PA | 16 KiB | 0x3e00 | USART0 | 404 B | 482 B | | ATmega168, 168A, 168P, 168PA | 16 KiB | 0x3e00 | USART0 | 400 B | 480 B |
| ATmega328, 328P | 32 KiB | 0x7e00 | USART0 | 404 B | 482 B | | ATmega328, 328P | 32 KiB | 0x7e00 | USART0 | 400 B | 480 B |
| ATmega164A, 164P, 164PA | 16 KiB | 0x3e00 | USART0 | 404 B | 482 B | | ATmega164A, 164P, 164PA | 16 KiB | 0x3e00 | USART0 | 400 B | 480 B |
| ATmega324A, 324P, 324PA | 32 KiB | 0x7e00 | USART0 | 404 B | 482 B | | ATmega324A, 324P, 324PA | 32 KiB | 0x7e00 | USART0 | 400 B | 480 B |
| ATmega644, 644A, 644P, 644PA | 64 KiB | 0xfe00 | USART0 | 398 B | 476 B | | ATmega644, 644A, 644P, 644PA | 64 KiB | 0xfe00 | USART0 | 394 B | 474 B |
| ATmega1284, 1284P | 128 KiB | 0x1fe00 | USART0 | 424 B | 502 B | | ATmega1284, 1284P | 128 KiB | 0x1fe00 | USART0 | 420 B | 500 B |
† No hardware boot section: the host patches the reset vector, and the budget † No hardware boot section: the host patches the reset vector, and the budget
is 510 bytes, since the slot's last word is the trampoline. is 510 bytes, since the slot's last word is the trampoline.
@@ -52,7 +52,7 @@ USART's own pins with the `OSCCAL` trim baked, 510 of its 512 — they alone
carry the far-flash machinery (ELPM reads, RAMPZ page commands), autobaud carry the far-flash machinery (ELPM reads, RAMPZ page commands), autobaud
alone carries the calibration loop, a bit-banged link on a USART's pins alone alone carries the calibration loop, a bit-banged link on a USART's pins alone
has to release it (below), and the trim adds its one register write. Without has to release it (below), and the trim adds its one register write. Without
the trim that build is 504; on the default pins, 502. The flash bank riding the trim that build is 504; on the default pins, 500. The flash bank riding
in a transfer's selector byte keeps even those chips' addressing the same in a transfer's selector byte keeps even those chips' addressing the same
16-bit form every other chip uses, which is why they are no longer the 16-bit form every other chip uses, which is why they are no longer the
outlier they were. outlier they were.

7
pureboot/pureboot.cpp
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@@ -351,9 +351,14 @@ consteval std::uint32_t window_polls()
return timeout_seconds * static_cast<std::uint32_t>(dev::clock.hz / link::poll_cycles); return timeout_seconds * static_cast<std::uint32_t>(dev::clock.hz / link::poll_cycles);
} }
// The countdown in the narrowest type that holds it: a fourth byte would
// cost a wider decrement chain at every poll for range most windows never
// use (the autobaud budget makes the same choice).
using window_t = std::conditional_t<window_polls() <= 0xffffff, avr::uint24_t, std::uint32_t>;
bool pending_before_deadline() bool pending_before_deadline()
{ {
std::uint32_t polls = window_polls(); window_t polls = window_polls();
do { do {
if (link::pending()) if (link::pending())
return true; return true;

6
tools/check.sh
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@@ -36,4 +36,10 @@ if ((full)); then
done done
fi fi
# Every tree is freshly built now — the one moment the README's size table
# can be held to what the images measure (a per-preset ctest sees only its
# own chip; the table needs all of them, and ungated it drifts: a
# common-code shave moves every row at once with nothing over budget).
python3 tools/sizes.py check-readme
echo "check: every chip green" echo "check: every chip green"