BlackMarkandClaude Opus 5.5
f9bc2cd8e2
Both alarms' registers come from one encoder that derives DY/DT and the mask bits from the rate, and the battery checks the bytes each Table 2 row writes instead of restating the enum values. Register addresses and bits are named, the year register is the year less 2000 rather than a division, and an alarm day reads back with one decode for both forms. Over the whole API the image is 10 B smaller on both parts; a rate only known at run time costs set_alarm1 6 B more. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
98 lines
4.2 KiB
Markdown
98 lines
4.2 KiB
Markdown
# ds3231
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Maxim DS3231 RTC driver on [libavr](https://git.blackmark.me/avr/libavr):
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clock and alarm read/write, alarm interrupts, oscillator-stop detection,
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die temperature. One source runs on every libavr chip — TWI hardware on
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the mega328P, open-drain software I2C on the tinies. All bus errors
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surface as `std::expected`.
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```cpp
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using bus = dev::i2c<{.frequency = 100_kHz}>;
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using rtc = ds3231::device<bus>;
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auto now = rtc::read_clock(); // result<date_time>
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auto armed = rtc::set_alarm1({}, ds3231::alarm1_rate::once_per_second);
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```
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`example/main.cpp` is a complete program. libavr rides as the `libavr/` submodule,
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pinned to the commit this driver builds against; `LIBAVR_ROOT` (cache or
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environment) overrides it for 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 attiny85-generated
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cmake --build --preset attiny85-generated
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```
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Presets cover attiny85/atmega328p in both libavr modes (generated and
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reflect); `ctest` runs the consteval battery over the BCD, the hours
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register's two formats, the weekday, the alarm registers each rate writes and
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the control and status write-backs, and holds the example to its stated size —
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**1468 B** on the mega328P and **1256 B** on the tiny85, byte-identical across
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the two modes. The legacy
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yazoalfa-based driver lives on the `master` branch.
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The weekday register is derived from the date by default. A program that
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assigns its own meaning to the device's 1..7 takes ownership of it, and no
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write here touches it:
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```cpp
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using rtc = ds3231::device<bus, ds3231::weekday_source::external>;
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```
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An alarm arms its INT/SQW output unless told otherwise, and can be muted and
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re-wired without re-arming:
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```cpp
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auto quiet = rtc::set_alarm2(at, ds3231::alarm2_rate::minutes_match,
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ds3231::alarm_interrupt::off);
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auto again = rtc::listen_alarm2();
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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/ds3231.atsln`
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builds `example/main.cpp` for both parts the presets cover, each to a
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**byte-identical `.text`** against the CMake build (`check-flags.py` below is
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what holds the flag sets equal, so the sizes are the presets' own), with the
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flags mirrored by hand. CMake remains the build system.
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`avrdevice` is a project-level property in Studio, so a part means a project, not
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a configuration: `ide/atmega328p/` and `ide/attiny85/`. They need separate
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directories rather than separate names — Studio builds into `<project
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dir>/<Configuration>` whatever `OutputDirectory` says, so two projects sharing
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one directory would also share one `example/main.o`, and building one after the
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other without a rebuild would link the other part's object.
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Studio finds libavr in the **submodule** at
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`$(MSBuildProjectDirectory)\..\..\libavr\include` — correct by construction,
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and anchored to the project because a plain relative path is resolved against
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the generated makefile's directory (the configuration's output directory), not
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the project's. There is no `LIBAVR_ROOT` escape hatch: a variable exported in a
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shell is invisible to Studio launched from the Start menu — which is what the
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submodule answers. It also needs a GCC 16.1 toolchain registered as flavour
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`avr-g++-16.1.0`, nothing older reaching `-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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for mcu in atmega328p attiny85; do
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case $mcu in atmega328p) device=ATmega328P;; attiny85) device=ATtiny85;; esac
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python libavr/tools/atmelstudio/componentinfo.py \
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"ide/$mcu/ds3231-$mcu.componentinfo.xml" --device "$device"
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python libavr/tools/atmelstudio/check-flags.py --solution ide/ds3231.atsln \
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--project "ds3231-$mcu" \
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--compile-commands "build/$mcu-generated/compile_commands.json" \
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--log "build/as-$mcu.log"
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done
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```
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One reference describes one part, hence `--project`. Release is what the gate
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compares, the presets defining no debug build; Debug carries the `-Og
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-gdwarf-4` pair libavr's own debug preset uses.
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Differences from legacy: weekday-rate alarms set the DY bit (the legacy
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driver always cleared it), each register block is read or written in one
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coherent bus transaction, and errors are reported instead of ignored.
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