BlackMark
2e9c929a19
`set_alarm1/2`'s `enable_interrupt = false` did nothing at all - it skipped the control-register write rather than clearing A1IE/A2IE - and there was no other way to clear them, so an alarm armed once with its interrupt on drove INT/SQW for good. It is `alarm_interrupt::off` now and it clears the bit, with `listen_alarm1/2()` and `mute_alarm1/2()` beside it for a caller that arms once and changes its mind later. The bare bool went with it (rule 37): `set_alarm1(at, rate, false)` said nothing at the point of use. `bool SetWeekday` was the same shape one level up - `device<bus, false>` names nothing - and its two writers disagreed about what it meant: `write_date` skipped the weekday register, `write_clock` stamped a placeholder 1 into it, so a program that turned the maintenance off still had the register overwritten and no way to set it. `weekday_source::external` now means the register is the program's, in both writers. test/consteval.cpp is the battery this driver never had, over the arithmetic that has no bus in it: the BCD round trip across every representable value and its nibble layout, the hours register in both formats including all four noon/midnight cases, Sakamoto's weekday against six calendar dates (leap day, the day after it, and 2100's missing leap), and both alarms' rate encodings transcribed against 19-5170 Table 2 - including that alarm 2's masks sit one place below alarm 1's, which is the property that makes one distribution loop wrong for the other. Red-green: two assertions fire on a flipped DY bit. Beside it, one decode rather than two: `read_clock` and `read_time` spelled the seconds/minutes/hours triplet out separately (rule 6). Every image byte-identical on both chips in both modes. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
ds3231
Maxim DS3231 RTC driver on libavr:
clock and alarm read/write, alarm interrupts, oscillator-stop detection,
die temperature. One source runs on every libavr chip — TWI hardware on
the mega328P, open-drain software I2C on the tinies. All bus errors
surface as std::expected.
using bus = dev::i2c<{.frequency = 100_kHz}>;
using rtc = ds3231::device<bus>;
auto now = rtc::read_clock(); // result<date_time>
auto armed = rtc::set_alarm1({}, ds3231::alarm1_rate::once_per_second);
example/main.cpp is the full tour. libavr rides as the libavr/ submodule,
pinned to the commit this driver builds against; LIBAVR_ROOT (cache or
environment) overrides it for development against a working tree:
git submodule update --init libavr
cmake --preset attiny85-generated
cmake --build --preset attiny85-generated
Presets cover attiny85/atmega328p in both libavr modes (generated and
reflect); ctest runs the consteval battery over the BCD, the hours
register's two formats, the weekday and the alarm rate encodings. The legacy
yazoalfa-based driver lives on the master branch.
The weekday register is derived from the date by default. A program that assigns its own meaning to the device's 1..7 takes ownership of it, and no write here touches it:
using rtc = ds3231::device<bus, ds3231::weekday_source::external>;
An alarm arms its INT/SQW output unless told otherwise, and can be muted and re-wired without re-arming:
auto quiet = rtc::set_alarm2(at, ds3231::alarm2_rate::minutes_match,
ds3231::alarm_interrupt::off);
auto again = rtc::listen_alarm2();
Atmel Studio
master carries a Studio solution, so this branch does too: ide/ds3231.atsln
builds example/main.cpp for both parts the presets cover, each to a
byte-identical .text against the CMake build (check-flags.py below is
what holds the flag sets equal, so the sizes are the presets' own), with the
flags mirrored by hand. CMake remains the build system.
avrdevice is a project-level property in Studio, so a part means a project, not
a configuration: ide/atmega328p/ and ide/attiny85/. They need separate
directories rather than separate names — Studio builds into <project dir>/<Configuration> whatever OutputDirectory says, so two projects sharing
one directory would also share one example/main.o, and building one after the
other without a rebuild would link the other part's object.
Studio finds libavr in the submodule at
$(MSBuildProjectDirectory)\..\..\libavr\include — correct by construction,
and anchored to the project because a plain relative path is resolved against
the generated makefile's directory (the configuration's output directory), not
the project's. There is no LIBAVR_ROOT escape hatch: a variable exported in a
shell is invisible 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 reaching -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/):
for mcu in atmega328p attiny85; do
case $mcu in atmega328p) device=ATmega328P;; attiny85) device=ATtiny85;; esac
python libavr/tools/atmelstudio/componentinfo.py \
"ide/$mcu/ds3231-$mcu.componentinfo.xml" --device "$device"
python libavr/tools/atmelstudio/check-flags.py --solution ide/ds3231.atsln \
--project "ds3231-$mcu" \
--compile-commands "build/$mcu-generated/compile_commands.json" \
--log "build/as-$mcu.log"
done
One reference describes one part, hence --project. Release is what the gate
compares, the presets defining no debug build; Debug carries the -Og -gdwarf-4 pair libavr's own debug preset uses.
Differences from legacy: weekday-rate alarms now actually set the DY bit
(the old setAlarmHelper always cleared it), reads/writes are single
coherent bus transactions, and errors are reported instead of ignored.