EC-20.4 Embedded Linux, Device Drivers and the Board Support Layer

Work through these

• The line between a microcontroller and an applications processor

  Memory management hardware, external memory and a storage device are what make a general-purpose operating system possible, and their absence is what makes a microcontroller predictable. Knowing which side of that line a part sits on decides most of the software structure.

  NPTEL: Embedded System Design with ARM (IIT Kharagpur) · Course

• Bootloader, kernel, root filesystem: what boots what, and in what order

  A board that will not start is almost always failing at one identifiable stage, and being able to name the stages turns a dead board into a question with an answer. Each stage also has its own way of telling you what it is doing.

• The device tree: describing hardware the kernel cannot discover

  A processor cannot enumerate the parts wired to its pins the way a computer enumerates a plug-in card, so the wiring is written down in a separate description the kernel reads at boot. Most bring-up work on a new board is edits to that description.

  NPTEL: Embedded System Design with ARM (IIT Kharagpur) · Course

• What a driver is: one kernel interface, one piece of hardware, and the mapping between

  A driver exposes a standard interface upward and talks to registers downward, and almost all of its complexity is in the middle. Reading one small existing driver end to end teaches more than any description of the model.

• User space against kernel space, and why most work belongs above the line

  Code in the kernel can crash the whole system and is far harder to debug, so the standard advice is to do as little there as the hardware allows. Several interfaces exist specifically to let ordinary programs reach hardware safely.

  NPTEL: Design for Internet of Things (IISc Bangalore) · Course

• What happens to your timing guarantees, and what a real-time kernel restores

  A general-purpose kernel will occasionally take milliseconds to get back to your code, which destroys any hard deadline. The usual answers are a real-time variant of the kernel, or leaving the hard timing on a separate small processor.

  NPTEL: Real-Time Systems (IIT Kharagpur) · Course