BlackMark
c01e583597
Six things the port had dropped or got wrong, and the one that matters is the last. The help is a table again — name, dots, description, one command per line — instead of a single line of bare words that said nothing about what any of them did. The layout is the original's, colons at column 12, which `bootloader` at ten characters is what sets. Abbreviations are back, and they were a feature: any prefix resolves to the first command it matches, so `up` is uptime and `st` is statistics. Order does the disambiguating, which is why the table is in the original's dispatch order and new entries go on the end — appending cannot take an abbreviation that already meant something. `reset` keeps the original's exception and must be typed in full: `r` should not be able to clear the histogram. The histogram gets its resolution back. The bar was capped at 40 columns where the original scaled to 100, and on a distribution this narrow that threw away most of the difference between neighbouring buckets. Same normalisation as before: divide by whatever makes the tallest bucket fit. The sample count moves to a fixed ten-column field before the bar, so the numbers read as a table instead of trailing off the ragged right end. `version` exists again, and this is 2.1 — 2.0 being the port as it stood. Added while here: `save`, to force the writeback that otherwise waits up to thirty minutes; the resistance in `show`, which is the one number that says *why* a temperature is wrong and which the original printed; a report when a line overflows the buffer rather than silently acting on its head; "no data yet" where there is none; and a blank line after each command's output. And the way out. `bootloader` now jumps rather than resetting, because pureboot hands straight back on WDRF by design — so the legacy watchdog-reset hand-over reaches it and opens no window, which on a board with no reset line is a board that cannot be reflashed. Two more bugs in the same three lines: the target was 0x7800, a 2 KB boot section's base, which on this board's 512-byte section reads erased and made the check false and the command a no-op; and UCSR0B was left set, which mutes a loader that bit-bangs the pin the USART still owns. All three are now read back out of the emitted image by ctest, the address and the watchdog red-proven against exactly the legacy behaviour they exist to catch. libavr advances to 71cfb2f. Verified on the board: FanTemp v2.1, min 0 C / max 74 C matching what 1.8b reported off the same EEPROM, the fan curve within one percentage point of the legacy double-precision one at every 5 C from 15 to 60, and `bootloader` -> pureboot 7 -> back to a running application. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
4.3 KiB
fantemp
v2.1. Temperature-controlled fan firmware (ATmega328P, 16 MHz), rewritten on
libavr: thermistor on ADC0 sampled
free-running and averaged over 1000 conversions, fan on OC0B at 50 kHz,
115200 Bd serial console (help lists the commands), temperature
histogram persisted to EEPROM, and a direct jump into a boot-section
bootloader at 0x7e00.
The EEPROM format is the legacy firmware's, unchanged: 100 little-endian
uint32 buckets at address 0, one per °C. A board carrying years of history
from FanTemp 1.8b keeps every count — verified on hardware, all 67 non-empty
buckets byte-identical across the conversion.
The console
Commands may be abbreviated to any unambiguous-by-order prefix, as the legacy
firmware allowed: up is uptime, st is statistics, sa is save. The
table order resolves ties, so s is show — and reset is deliberately the one
command that cannot be abbreviated, because r should not be able to wipe the
histogram. save (new) forces a writeback, which otherwise happens every 30
minutes and on the way into the bootloader.
Reaching the bootloader
bootloader jumps; it does not reset. That is not a style choice:
- pureboot hands straight back on WDRF, by design — an unattended board that watchdog-resets in a loop must not sit in a loader. So the legacy watchdog-reset hand-over arrives and opens no window at all, and on a board with no reset line that is a board that cannot be reflashed.
- The address is
0x7e00, the top 512 bytes. The legacy firmware used0x7800, a 2 KB boot section's base, which on a board with a 512-byte boot section reads erased — so itsbootloadercommand silently never arrived anywhere. UCSR0Bis cleared first. WhileTXEN0is set the USART owns PD1, so a loader that bit-bangs the same pin receives perfectly and answers into nothing.
ctest reads all three back out of the emitted image (test/check_reachability.py),
because none of them is visible from the source alone and the failure mode is an
unreflashable board. Both the address and the watchdog checks are red-proven
against the legacy behaviour they exist to catch.
The Steinhart–Hart math of the legacy firmware (runtime doubles + libm log) is gone: the Beta equation and the cubic fan curve are evaluated consteval into flash tables — the firmware itself never touches floating point.
libavr rides as the libavr/ submodule, pinned to the commit this firmware
builds against; LIBAVR_ROOT (cache or environment) overrides it for
development against a working tree:
git submodule update --init libavr
cmake --preset atmega328p-generated
cmake --build --preset atmega328p-generated
Atmel Studio
master carries a Studio solution, so this branch does too: ide/fantemp.atsln
builds the same firmware — byte-identical .text and .data to the CMake
build — from the same sources, with the flags mirrored by hand.
Studio finds libavr in the submodule, at
$(MSBuildProjectDirectory)\..\libavr\include — correct by construction, and
anchored to the project rather than written relative to the generated makefile,
which runs from the configuration's output directory and would need a different
number of ... Unlike the CMake build there is no LIBAVR_ROOT to point
elsewhere: an environment variable set in a shell is not visible to Studio
launched from the Start menu — which is what the submodule answers.
It also needs a GCC 16.1 toolchain registered as flavour avr-g++-16.1.0;
nothing older can compile -std=c++26.
One generated file is required before the project will load, and one command
checks the flags have not drifted (both from libavr's tools/atmelstudio/):
python ../libavr/tools/atmelstudio/componentinfo.py \
ide/fantemp.componentinfo.xml --device ATmega328P
python ../libavr/tools/atmelstudio/check-flags.py --solution ide/fantemp.atsln \
--compile-commands build/atmega328p-generated/compile_commands.json \
--log build/atmelstudio.log
CMake remains the build system; the solution is there so the project opens in
Studio as its predecessor did. Only the Release configuration is gated against
CMake — the presets define no debug build — and Debug carries the -Og -gdwarf-4 pair libavr's own debug preset uses.
Legacy (yazoalfa submodules) stays on master.