Timezone database

The firmware’s timezone list is a binary resource (RESOURCE_ID_TIMEZONE_DATABASE) built from an IANA tzdata snapshot (resources/normal/base/tzdata/timezones_olson.txt) by tools/timezones.py, wired into the resource build by tools/cmake/resources.py. It is read by fw/services/timezone_database/service.c; the DST-rule struct is TimezoneDSTRule in include/pbl/services/timezone_database.h.

Layout (little-endian): a 6-byte header, then region records, DST rules and link records.

Region records — 24 bytes each

Field	Size	Notes
continent index	1	into a fixed 10-entry list: Africa, America, Antarctica, Asia, Atlantic, Australia, Europe, Indian, Pacific, Etc
city name	15	NUL-padded; full name is `continent/city`
GMT offset	2	`int16_t`, minutes
tz abbreviation	5	NUL-padded; may contain `*` as a `%s` placeholder for the D/S letter
DST rule id	1	0 = no DST

DST rules — 16 bytes per id

Each DST id owns a pair of 8-byte TimezoneDSTRule records, start rule then end rule:

Field	Size	Notes
`ds_label`	1	`'D'` enter DST, `'S'` leave, `'\0'` none
`wday`	1	0 = Sunday; 255 = any day
`flag`	1	bit 0: “last ” (day-decrement); bit 1: rule time is standard time; bit 2: UTC; bit 3: wall time (written by the builder, never read — wall time is the firmware default)
`month`	1	0-based
`mday`	1	1-based
`hour`, `minute`	2
padding	1

Rule id 0 (“no DST”) is counted in dst_rule_count but not stored, so rule id n lives at (n - 1) × 16 bytes into the section. The mapping from tzdata rule names to ids (dstzone_list in tools/timezones.py) is append-only: the firmware hardcodes some ids (e.g. Brazil = 6), so the order must never change between database releases.

Link records — 35 bytes each

uint16_t region_id plus a 33-byte NUL-padded alias (sized for the longest IANA name). Links resolve legacy aliases — old mobile OSes still send names like US/Pacific — to a region record.

PebbleOS

Timezone database

Header

Region records — 24 bytes each

DST rules — 16 bytes per id

Link records — 35 bytes each

Overview