Daniel Samson
8a38540312
Adds real (calendar) time, the foundation for filesystem timestamps. Monotonic time (`clock`) says how long since boot; this says what time it actually is. - cpu.zig (x86_64): readRtcUnixSeconds() reads the CMOS real-time clock (ports 0x70/0x71) — waits out an update-in-progress, reads twice until stable, handles BCD-vs-binary and 12-vs-24-hour per status register B — and converts to Unix epoch seconds (UTC). - kernel/wall-clock.zig: reads the RTC once at boot and anchors it to the monotonic clock, so a query is a cheap arithmetic offset — no per-call CMOS poll, no lock, no SMP hazard on the shared ports. kmain calls init() once the monotonic clock is final and logs the epoch. - wall_clock() syscall (33) -> Unix epoch seconds, wrapped by runtime.system .wallClock(). Wall-clock *seconds* are mechanism the kernel owns like the monotonic clock; calendars/timezones are user-space policy (the stale comment on systemClock that called wall-clock a "user-space service" is updated in spirit by the new handler's doc). - A `wall-clock` kernel test asserts the boot RTC read is a plausible current epoch. Verified against the host: the guest read epoch 1783971244 while `date -u +%s` gave 1783971245 (one second of boot lag) — the CMOS read + epoch conversion are correct to the second. zig build, zig build test, and smoke/clock/init are green.
27 lines
1.1 KiB
Zig
27 lines
1.1 KiB
Zig
//! Wall-clock time: the CMOS real-time clock read once at boot and anchored to the
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//! monotonic clock, so a query is a cheap arithmetic offset — no per-call CMOS poll,
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//! no lock, no SMP hazard on the shared 0x70/0x71 ports.
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//!
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//! Wall-clock *seconds* are mechanism the kernel owns, exactly like the monotonic
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//! clock ([[time-architecture]]): reading the hardware's value is not policy.
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//! Calendars, timezones, and formatting layer on top in user space. It exists so the
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//! filesystem can stamp real timestamps (mtime) — see docs/zig-self-hosting.md.
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const architecture = @import("architecture");
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var boot_unix_seconds: u64 = 0;
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var boot_nanos: u64 = 0;
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/// Read the RTC once and anchor it to the monotonic clock. Call at boot, after the
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/// monotonic clock is calibrated.
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pub fn init() void {
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boot_unix_seconds = architecture.readRtcUnixSeconds();
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boot_nanos = architecture.nanos();
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}
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/// The current wall-clock time in Unix epoch seconds (UTC): the boot RTC value plus
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/// the monotonic time elapsed since. Zero until `init` runs.
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pub fn nowSeconds() u64 {
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return boot_unix_seconds + (architecture.nanos() -% boot_nanos) / 1_000_000_000;
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}
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