BlackMark
0f5e40510c
8382 -> 8004 B of flash, 725 -> 511 B of RAM on a part that has 2048. The command names were a std::to_array of string_view, and on a Harvard machine that is the worst of both: the characters land in .data and so does the table's own pointer-and-length pair for each of them, so the firmware carried 216 B of RAM for thirteen words that never change - and paid for them in flash too, since .data is copied out of an initialiser image at startup. They are one NUL-separated blob in flash now, walked with lpm. Separators rather than an offset table, because an offset table is the RAM this exists to give back; the names sit in it in match order, so the walk that finds a name is the same walk that compares it and measures it. Flash falls further than RAM does: the initialiser image and the two tables were 216 B of it, and the blob is 87. The header said the names "cannot" be in flash because they are matched at run time. Being matched at run time is not a reason to be in RAM on a machine with two address spaces - only being *written* is, and nothing writes these. Two smaller things came with it. `reset`'s exact-match rule was a bool on every entry to protect one; it is an index found by searching the list, so reordering the commands cannot move the protection onto a different one. And `version` was the last string_view left, holding its own characters and a pointer to them. The matching is now pinned rather than assumed: lookup() is constexpr and the battery asserts the load-bearing order the README documents - `s` is show and not statistics, `st` is statistics, no abbreviation of `reset` resolves, and `helpful` is not `help`. Red-checked by claiming `s` is statistics. Both modes byte-identical, ten tests green. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
106 lines
5.1 KiB
Markdown
106 lines
5.1 KiB
Markdown
# fantemp
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**v2.2.** 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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`show`, `statistics` and the histogram print one value per line behind a dotted
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label, the way the original did — a run-on line is fine for one reading and
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unreadable when `monitor` emits one a second. `curve` walks every whole degree
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from 10 to 60 with a bar, because the curve is a cubic and five-degree samples
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without a graph show none of its shape.
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**Ctrl+C** abandons a half-typed line and gives a fresh prompt, echoing `^C`, and
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it is what stops `monitor`. Stopping on *any* byte, which is what the port did
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first, reads well right up until a host sends a line ending: `monitor\r\n` then
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stopped itself on the `\n` it arrived with, one reading in.
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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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The firmware is **8004 B** of flash, byte-identical between the generated and
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reflect modes, and `ctest` holds it to that number.
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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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