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RTC_RX8130CE writes and reads the one-hot WEEK register as a number

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@ptr727 is already working on this.

Since Oct 4, 2026.

  • #3550 by @ptr727 — open

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
c
Domain
embedded-iot

Research direction

Read src/helpers/RTC_RX8130CE.cpp, especially setTime() and getTime(), alongside the RX8130CE manual's week counter section. Update the write and read handling to use the one-hot weekday encoding described in the issue, including the stated behavior for old multi-bit values. Done when all seven weekdays round-trip correctly and an old multi-bit value decodes to its lowest set bit.

Written by the indexing model from the issue text.

Description

RTC_RX8130CE writes and reads the RX8130CE's WEEK register as a number. The chip encodes the day of the week one-hot, so on some days it holds no day at all, and on others it holds two days at once.

References:

The defect

§14.1.2 "Week counter" (p. 27) says the day of the week "is indicated by 7 bits, bit 0 to bit 6", counted as 01h → 02h → 04h → 08h → 10h → 20h → 40h → 01h. Table 15 sets Sunday = 01h through Saturday = 40h, and the manual says: "Do not set '1' to more than one day at the same time."

  • setTime() L98 writes bin2bcd(t->tm_wday) & 0x07. That gives:

    • Sunday (0): 00h, no day set.
    • Wednesday (3): 03h, Sunday and Monday both set.
    • Friday (5): 05h, Sunday and Tuesday both set.
    • Saturday (6): 06h, Monday and Tuesday both set.
    • Monday (1), Tuesday (2) and Thursday (4): 01h, 02h and 04h. Each is a single bit, but for the wrong day: Sunday, Monday and Tuesday.

    No day of the week is stored correctly.

  • getTime() L144 decodes it the same way, bcd2bin(buff[3] & 0x07), so a correctly encoded register (Thursday = 10h) would read back as 0.

Impact

Low. now() and unixtime() go through mktime(), which ignores tm_wday, so the date and time MeshCore uses are unaffected. What is wrong is the chip's own week counter:

  • It holds an invalid value, which the manual tells you not to write.
  • On a Sunday it holds no day at all.

That matters for a weekday alarm, which MeshCore doesn't use, and for any other firmware that reads the chip.

Proposed fix

  • Write: 1 << t->tm_wday.
  • Read: decode the position of the set bit, taking the lowest set bit when a chip still holds an old multi-bit value.

There are no other callers: tm_wday is written and read only in these two places.

The same defect was found independently in ZephCore: ptr727/liquidraver-ZephCore#39.

Dominant language
C
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Avg merge
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Merged PRs (30d)
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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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