BlackMark
e56e8b977f
608 B of flash, 7.6 % of the image, and it is not available: this board runs continuously and an uptime that restarts every 49.7 days is not acceptable, which is what a 32-bit millisecond counter wraps at. The tick split goes with it. It only ever made sense beside the narrowing, and on its own it costs 66 B to buy about 0.4 % of a CPU nothing here is competing for. Both are recorded rather than deleted, and that is the point of the change: the numbers are real and re-measurable, so someone will find 608 B again and read it as an opportunity. What they need with it is the reason it was refused. Docs only; five tests green. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
41 lines
1.7 KiB
Markdown
41 lines
1.7 KiB
Markdown
# Tasks
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This file is current work. The repo is the sole task tracker (libavr guidance
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rule 20).
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## Open
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Nothing.
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## Decided against
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Both of these are measured, and both are recorded here rather than deleted so
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that the next person to measure them does not read a number as an opportunity
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and re-propose work the owner has already refused.
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### The millisecond clock stays 64 bits
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Narrowing `uptime::millis()` and the three timestamps that hold its value from
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`uint64_t` to `uint32_t` is **608 B of flash, 7.6 % of the image** (8004 B down
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to 7396), plus 16 B of RAM.
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**Refused, owner-stated: this board runs continuously and an uptime that
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restarts every 49.7 days is not acceptable.** That is what a 32-bit
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millisecond counter wraps at, and the display is not the only cost - the
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interval tests would have to become subtractions, since `now - last >=
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interval` survives a wrap where `now >= last + interval` does not, and
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`terminal.hpp`'s monitor tick is written the second way. The 64-bit counter is
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what puts the wrap out of reach, which is the property being bought.
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### The 1 kHz tick keeps its 64-bit increment
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The compare handler increments 64 bits, so it calls libgcc's `__adddi3_s8`, and
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a call inside a signal handler decides the prologue - twelve push/pop pairs for
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what the helper might clobber. Splitting the counter into two 32-bit halves
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removes the call and keeps the full range, taking the handler from ~47
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instructions to ~26 with the carry running once every 49.7 days.
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**Refused: it costs 66 B of flash to buy about 0.4 % of the CPU**, and nothing
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here is timing-critical. It was only ever worth considering alongside the
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narrowing above, which is refused outright.
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