The program date
The date of the machine: this service reads the real-time clock of the machine (the CMOS clock, ports 0x70 and 0x71) at its start and each 10 seconds, and writes in the date page the date of the time 0 of the system. Each program reads the date from the page and the time page, with no kernel entry and no call (contract/date).
A driver of a clock is a program, not a part of the kernel: the root service gives this program the two ports and the page with the right Write, and nothing else.
The clock gives whole seconds. The service waits for the clock to change its second, so the date of the time 0 is exact to about one millisecond. The clock of the machine keeps UTC (QEMU: -rtc base=utc). Leap seconds are not counted. The year has two digits: the dates are from 2020 to 2099 (support/calendar, clock_seconds).
| Fact | Value |
|---|---|
| Source | programs/date |
| Boot image | in the boot image; the image is not built, so its size is not known |
| Imports | none |
| Imported by | none |
Exports
| Export | What it does |
|---|---|
| now() -> Date | gives the date and the time of day in UTC, from the date page and the time page: the same value that each program reads with no call |
| entry() |
Read from the source of the module, as the build reads it to describe the exports (tools/kerneltool/describe.odin).
What the root service gives it
| What | Value | As the root service says |
|---|---|---|
| Grants | {.Clock, .Serve} | It reads the real-time clock, writes the date page, and serves now(). |
| Budget: pages, programs, threads | {pages = 2048, programs = 1, threads = 1} | Not named in things_of: the budget of each other program. |
Read from grants_of and things_of in programs/root/main.odin; budget_of in the same file adds the limits of processor time and of log records.