Startup time after power-up is not consistent

Published: 17 October 2024 · Status: Open — no fix recorded in any release · Last reviewed: 2026-08-07

Affected

All devices. This is in the bootloader, which runs before any firmware version or configuration is involved, so no setting changes it.

What happens

The device takes a random amount of time to start after power is applied. Not a long time — a variable one. Power the same system up twice and the device is ready at a different moment each time.

That matters wherever something else expects the device to be present at a predictable point in the power-up sequence. A module that starts talking before the device is listening, or that decides the device is absent because it did not answer in time, will behave differently from one power cycle to the next — and intermittent-on-startup is among the least pleasant things to diagnose.

Why

The bootloader is the small program that runs first at power-up: it brings the hardware up and hands over to the main firmware. Something in that sequence does not take a fixed amount of time.

I have not published the root cause, and I am not going to guess at one here. The original notice recorded the behaviour and that it was being investigated.

What to do

There is no firmware fix to update to, so this is a design constraint rather than a defect to clear:

  • Do not build a startup sequence that depends on the device being live at a fixed moment after power. Anything that must wait for the device should wait for it to respond, not for a timer to expire.
  • Give it time before deciding it is absent. A module that reports the device missing immediately after power-up may simply have asked early.
  • On a bench, power the device first and let it settle before bringing up whatever talks to it.

If a symptom only ever appears on the first few seconds after power-up and never afterwards, this is worth suspecting before the wiring.

Status

Open. The original notice said the cause was under investigation and that an update would follow in a later release. Searching the release history for any bootloader or startup-timing entry finds nothing, so as of this review no fix has been published.