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>
92 lines
4.3 KiB
Markdown
92 lines
4.3 KiB
Markdown
# fantemp
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**v2.1.** Temperature-controlled fan firmware (ATmega328P, 16 MHz), rewritten on
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[libavr](https://git.blackmark.me/avr/libavr): thermistor on ADC0 sampled
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free-running and averaged over 1000 conversions, fan on OC0B at 50 kHz,
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115200 Bd serial console (`help` lists the commands), temperature
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histogram persisted to EEPROM, and a direct jump into a boot-section
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bootloader at `0x7e00`.
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The EEPROM format is the legacy firmware's, unchanged: 100 little-endian
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`uint32` buckets at address 0, one per °C. A board carrying years of history
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from FanTemp 1.8b keeps every count — verified on hardware, all 67 non-empty
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buckets byte-identical across the conversion.
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## The console
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Commands may be abbreviated to any unambiguous-by-order prefix, as the legacy
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firmware allowed: `up` is `uptime`, `st` is `statistics`, `sa` is `save`. The
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table order resolves ties, so `s` is `show` — and `reset` is deliberately the one
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command that cannot be abbreviated, because `r` should not be able to wipe the
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histogram. `save` (new) forces a writeback, which otherwise happens every 30
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minutes and on the way into the bootloader.
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## Reaching the bootloader
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`bootloader` **jumps**; it does not reset. That is not a style choice:
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- **pureboot hands straight back on WDRF**, by design — an unattended board that
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watchdog-resets in a loop must not sit in a loader. So the legacy
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watchdog-reset hand-over arrives and opens no window at all, and on a board
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with no reset line that is a board that cannot be reflashed.
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- The address is `0x7e00`, the top 512 bytes. The legacy firmware used `0x7800`,
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a 2 KB boot section's base, which on a board with a 512-byte boot section reads
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erased — so its `bootloader` command silently never arrived anywhere.
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- `UCSR0B` is cleared first. While `TXEN0` is set the USART owns PD1, so a loader
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that bit-bangs the same pin receives perfectly and answers into nothing.
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`ctest` reads all three back out of the emitted image (`test/check_reachability.py`),
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because none of them is visible from the source alone and the failure mode is an
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unreflashable board. Both the address and the watchdog checks are red-proven
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against the legacy behaviour they exist to catch.
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The Steinhart–Hart math of the legacy firmware (runtime doubles + libm
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log) is gone: the Beta equation and the cubic fan curve are evaluated
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consteval into flash tables — the firmware itself never touches floating
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point.
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libavr rides as the `libavr/` submodule, pinned to the commit this firmware
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builds against; `LIBAVR_ROOT` (cache or environment) overrides it for
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development against a working tree:
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```sh
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git submodule update --init libavr
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cmake --preset atmega328p-generated
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cmake --build --preset atmega328p-generated
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```
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## Atmel Studio
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`master` carries a Studio solution, so this branch does too: `ide/fantemp.atsln`
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builds the same firmware — byte-identical `.text` and `.data` to the CMake
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build — from the same sources, with the flags mirrored by hand.
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Studio finds libavr in the **submodule**, at
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`$(MSBuildProjectDirectory)\..\libavr\include` — correct by construction, and
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anchored to the project rather than written relative to the generated makefile,
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which runs from the configuration's output directory and would need a different
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number of `..`. Unlike the CMake build there is no `LIBAVR_ROOT` to point
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elsewhere: an environment variable set in a shell is not visible to Studio
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launched from the Start menu — which is what the submodule answers.
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It also needs a GCC 16.1 toolchain registered as flavour `avr-g++-16.1.0`;
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nothing older can compile `-std=c++26`.
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One generated file is required before the project will load, and one command
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checks the flags have not drifted (both from libavr's `tools/atmelstudio/`):
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```sh
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python ../libavr/tools/atmelstudio/componentinfo.py \
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ide/fantemp.componentinfo.xml --device ATmega328P
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python ../libavr/tools/atmelstudio/check-flags.py --solution ide/fantemp.atsln \
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--compile-commands build/atmega328p-generated/compile_commands.json \
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--log build/atmelstudio.log
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```
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CMake remains the build system; the solution is there so the project opens in
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Studio as its predecessor did. Only the Release configuration is gated against
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CMake — the presets define no debug build — and Debug carries the `-Og
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-gdwarf-4` pair libavr's own debug preset uses.
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Legacy (yazoalfa submodules) stays on `master`.
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