Board-level Linux integration, U-Boot, device trees, kernel drivers and peripheral bring-up. Separate power and hardware checks from software adaptation, and define a recoverable boot path.
Use Linux clock-rate exclusivity to protect a bounded interval in which another consumer must not change the relevant clock rate. Balance every acquired claim and distinguish a genuinely blocked rate change from a successful no-op. This API is counted rate protection, not a mutex that makes a second acquisition wait until the first owner leaves….
A recovery reset belongs to every device affected by the physical reset line, even when only one driver requested it. Map those consumers before attempting recovery. With Linux shared reset controls, an assert call may legitimately leave the line deasserted because a healthy peer still needs it released; successful API return is not proof that…
Moving a signal from a memory-mapped SoC GPIO to an I2C expander can change the legal execution context of the same-looking GPIO operation. Audit the provider and use a sleepable path when required. Adding the _cansleep suffix does not make a hard-interrupt handler sleepable; the operation must move to a suitable thread or other permitted…
Choose one software meaning for assertion and let the GPIO descriptor map it to the required controller-pin level. In the Linux descriptor API, logical one means active; it does not always mean a measured high voltage. A second inversion in application code can silently undo the board description and reverse a reset or enable signal….
A Linux I2C mux transaction has a route-selection phase, a target transfer, and an optional deselection phase. The locking model determines which other transfers may occur between those phases. Review that exact model and the complete upstream topology before adding a lock: an extra parent-adapter acquisition can deadlock a mux callback, while a missing topology…
Build the IIO scan layout from enabled-channel metadata, then decode each field using its own storage width, byte order, shift, and signedness. A packed C structure or a list sorted by channel name can produce believable values while reading padding or the wrong channel. Applicability: this article pins Linux v6.12. The original Python 3 example…
Define three representations before sending a non-byte SPI frame: the numerical word, its bytes in host memory, and its bits on the wire. A correct value in a debugger does not prove that a byte-oriented wrapper, transfer length, or controller word-width setting will produce the intended clocks. Applicability: this procedure uses the Linux v6.12 SPI…
Map transmitted and received bits on the same clock timeline. SPI clocks both directions, but the peripheral protocol decides which received bits have meaning. Discarding “all command bytes” can lose valid response bits when command and response fields share a host byte. Applicability: the concrete example is Microchip MCP3008 using the three eight-bit-segment framing in…
Translate the peripheral timing diagram into idle level, launch edge, and sample edge before changing SPI frequency. A clock rate reduction cannot make an incorrect edge contract correct. It may only make an accidental timing margin look reliable enough to hide the defect. Applicability: the concrete device is Analog Devices ADXL345 in four-wire SPI, datasheet…
Using a bundle’s signing time changes the time at which its certificate chain is evaluated; it does not prove when the signature was actually created. Review that distinction before treating an expired signing certificate as an operational nuisance that a configuration switch can solve. This analysis pins RAUC 1.14 and uses OpenSSL 3.0.18 source for…