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TPL5111 hardware watchdog timer not suppressible by firmware

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評価

難易度
5/5
見積もり時間
1週間以上
初心者へのやさしさ
30/100
issue の種類
機能追加
明瞭さ
説明が足りない
活発さ
静か
技術スタック
embedded-iot
領域
embedded-iot

調査の方向性

Inspect the hardware schematic and PCB connections for the TPL5111, the DONE signal to the ATmega1284P, and the DELAY resistor. Verify the IC designator and resistor value, calculate the current timeout, and determine whether the revision should document firmware feeding or pursue the proposed firmware-controlled enable; done means the timeout and selected approach are confirmed.

索引モデルが issue の本文から書いたものです。

説明

enhancement

Summary

The TPL5111 (nano-power timer) is used as a hardware watchdog that periodically resets the board if the MCU fails to strobe the DONE pin. Once the TPL5111 is active, firmware has no way to disable or extend the timeout beyond the hardware-set interval — if the board needs to perform a long-duration operation (e.g., writing a large log file, waiting for cellular registration, firmware OTA update), it must continuously strobe DONE or risk a spurious reset.

Specific concerns

OTA firmware update:
The Particle B-Series module supports OTA firmware updates. An update can take several minutes depending on cellular conditions. If the TPL5111 timeout is shorter than the OTA window and firmware is unable to strobe DONE while the modem is occupied, the board will reset mid-update, potentially corrupting the firmware image.

Cellular registration:
In poor-signal areas, initial cellular registration (attach + PDP context) can take 2–10 minutes. The ATmega must strobe DONE during this window, which means firmware must handle the TPL5111 feed loop separately from the cellular wait loop.

Long sensor acquisition:
Some sensor integrations (e.g., SDI-12 sensor with long command timeout) block the MCU for extended periods. If these exceed the watchdog interval, a reset occurs.

TPL5111 timeout setting

The timeout is set by a single resistor on the TPL5111 DELAY pin. This is a fixed hardware value and cannot be changed in software.

Recommended approaches

Option A — Firmware must always strobe DONE:
Accept the current design and require firmware to be structured around always being able to strobe DONE within the timeout period. Document the timeout value prominently for firmware authors.

Option B — Add a firmware-controlled enable on TPL5111 (preferred):
The TPL5111 has an active-low enable pin (!EN or equivalent — verify in datasheet). If connected to a GPIO rather than hard-wired to GND, firmware can:

  • Disable the watchdog before entering a long operation
  • Re-enable it afterward
    This is a hardware change requiring a PCB respin.

Option C — Increase the timeout resistor:
Set the DELAY resistor for a longer timeout (maximum is ~7200 s per the datasheet). Longer timeout reduces protection efficacy but reduces the risk of spurious resets during legitimate long operations.

Affected components

  • U? (verify designator): TPL5111 nano-power timer
  • DONE signal connection to IC1 (ATmega1284P) GPIO
  • DELAY resistor (verify designator and value)

Action required for current revision

Confirm the timeout value set by the DELAY resistor and document it. Ensure all planned firmware use cases (OTA, cellular registration, long sensor reads) can feed the watchdog within that interval.

🤖 Generated with Claude Code

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