CHIME

> Network time sync for DOS.

NetISA suite app. Asks the network for the current time, sets the DOS clock. v1.0 uses HTTPS HEAD and parses the response Date: header. SNTP and NTS over UDP land in v1.1/v1.2 once NetISA exposes UDP.

CHIME 1.0 running in DOSBox-X with the /STUBNET flag. White-on-black terminal output reads: CHIME 1.0.0; NetISA: stub mode; Server: time.cloudflare.com (HTTPS HEAD); Time: 2026-04-25 14:30:42 UTC; Now: 2026-04-25 08:06:28 (DOS clock); Delta: +23054 seconds; Write to DOS clock? [Y/n]. — CHIME report and confirmation prompt. /STUBNET activates the synthetic backend so the captured frame is reproducible.

Mode captures

CHIME with /STUBNET /DRYRUN: same report as the default, but the tail line reads 'DOS clock NOT set (dry run or declined)' and the program returns to the DOS prompt without writing. — `/DRYRUN`: report only, never write.

CHIME /HELP: prints the flag reference. Lists /AUTO, /DRYRUN, /QUIET, /VERBOSE, /SAFE, /STUBNET, /VERSION, /HELP, /SERVER=host, /PATH=/foo, /PORT=443, /MODE=xxx, /TZ=+/-HH:MM, each with a short description. — `/HELP`: cmdline reference.

CHIME 1.0
NetISA: ready (firmware 1.0.0, IP 192.168.1.42)
Server: time.cloudflare.com (HTTPS HEAD)
Time:   2026-04-25 14:30:42 UTC (-08:00 = 06:30:42 local)
Now:    2026-04-25 06:30:39 (DOS clock)
Delta:  +3 seconds
Write to DOS clock? [Y/n]

Status

2026-04-25. Compiles clean under Open Watcom V2. CHIME.EXE is 28 KB. TESTTIME reports 21 of 21 parser and stub-query assertions green.

What is in the tree:

src/chime.c, chime.h: main flow.
src/cmdline.c, config.c: /AUTO, /DRYRUN, /SAFE, /STUBNET, /SERVER=, /PATH=, /PORT=, /MODE=, /TZ=; CHIME.CFG reader/writer.
src/netisa_api.c: subset of the INT 63h API CHIME uses, plus a stub backend for /STUBNET.
src/timesrc.c: HTTP Date: parser (RFC 7231 IMF-fixdate), worldtime JSON parser, unix_ts conversion, query orchestrator.
src/dos_clock.c: INT 21h AH=2Bh/2Dh date+time set, CMOS RTC write-through via ports 0x70/0x71.
src/ui_status.c: terminal output, [Y/n] prompt.
test/testtime.c: parser roundtrip, stub query.
Makefile, README.md.

Why HTTP, not SNTP

NTP/SNTP run over UDP. The NetISA TSR INT 63h API as of v1.0 carries TLS sessions and plaintext TCP. No UDP yet. So CHIME v1.0 talks HTTPS HEAD to time-anchor URLs (time.cloudflare.com, time.google.com, worldtimeapi.org) and parses the Date: response header. One-second precision. v1.1 adds SNTP over UDP when NetISA exposes the UDP group. v1.2 adds NTS-KE / NTS over UDP.

Setting the clock

Three layers. CMOS RTC at I/O ports 0x70/0x71 (persists). BIOS tick at 0040:006C, 18.2 Hz (resets on reboot). DOS internal date/time via INT 21h AH=2Ah/2Ch get and AH=2Bh/2Dh set.

On modern DOS (MS-DOS 5+, FreeDOS) the INT 21h set propagates to CMOS. On older DOS (3.3, OEM 4.x) it does not, and the next reboot loses the change. CHIME does a direct CMOS write after the INT 21h call as a backstop: stop RTC updates by setting bit 7 of register 0x0B, BCD-encode and write seconds (reg 0), minutes (2), hour (4), day (7), month (8), year-mod-100 (9), century (32), then resume.

Timezone is fixed-offset (/TZ=-08:00). DST is not handled.

Usage

CHIME                          sync, prompt before writing
CHIME /AUTO                    sync, write without prompt
CHIME /DRYRUN                  report only, never write
CHIME /SERVER=time.google.com  override server
CHIME /TZ=-08:00               local timezone offset
CHIME /MODE=https-head         specific time source
CHIME /STUBNET                 use stub backend, no NetISA needed
CHIME /VERSION                 print version, exit
CHIME /HELP                    flag list

Roadmap

v1.0: HTTPS HEAD + JSON GET + plain HTTP fallback. Confirmation prompt UI. INT 21h + CMOS write-through.
v1.1: SNTP over UDP when NetISA exposes the UDP group. Sub-second precision, becomes default.
v1.2: NTS over UDP per RFC 8915.
v1.3: CHIME.TSR resident with periodic resync, INT 21h hooks for transparent correction.
v1.4: Optional COM-port time source for serial GPS receivers (1PPS + NMEA).
v1.5: Multi-server median consensus, drift trend reporting.

Hardware

Floor286 + 256KB

DOS3.3+

NetworkNetISA TLS path

ToolchainOpenWatcom V2

StandardC89/C90

LicenseMIT