install zephyr

• west init: install zephyr in current folder with default yml
  • we can init with a manifest file
    • the manifest file will have its own repo
    • other repos can be included as module
  • forest topology
• use modules to define out of tree board, dts, drivers, etc
  • repo should contain zephyr/module.yml
  • Reference
  • kconfig extensions

Kconfig

• Reference
• build/zephyr/.config is generated based on the following sources
  • board config <BOARD>_defconfig
  • CMAKE cache CONFIG_
  • application conf file: prj.conf and etc
• Kconfig item without label is invisible in menuconfig

board porting

• Reference
• Kconfig.board
  • define options in menuconfig
• board specific kconfig defaults
  • Kconfig.defconfig: invisible Kconfig symbols
  • <BOARD>_defconfig: visible Kconfig symbols

device tree

• Specification
• Reference
• each node is named like [label:] node-name[@unit-address]
• node-name should describe teh general class of device
  • tree struct starts from root node /
• unit-address: differentiate node based on bus address, but for naming purpose only
  • actual bus address is determined by node’s reg property
    • reg is constructed by concat address + size (i.e. offset)
  • #address-cells, #size-cells: specified by parent bus controller
    • #address-cells: number of <u32> cells in reg for address
    • #size-cells: number of <u32> cells in reg for size
• label: unique shorthand for identifying node
  • a node can have zero, one, or multiple node labels
  • translate into phandle which compiling
• node property
  • compatible: specify driver to be used
  • node name is contained in property
    • label: device_get_binding()
    • name: ?
• /aliases: gloabl section for node name to label mapping

• /chosen: describe non-hardware parameters. ex. bootargs

• device tree puts no contraint over its content
  • dts/bindings: enforce tree structure & parsing requirement.
  • dt_schema: used in linux kernel with slight different definition

device access

• get node id
  • cannot assign to variable
  • DT_PATH(): from tree path
  • DT_NODELABEL(): from node_label
  • DT_ALIAS(): from /aliases
  • DT_INST(): get one compatible device via its instance number
    • order of instance is not guaranteed
• get node label
  • DT_LABEL
• get device binding
  • notice that device loading depend on priority

device driver

• struct device *
  • config: build time configuration
  • data: driver data
  • api: sub system api

macro

• device tree content will be convert to macro with the help of bindings
  • if a matching driver is not found
    • the compilation still pass
    • the device is not used
    • the dt entry can get accessed
• driver macro defined as #define DT_DRV_COMPAT ...
  • if dt macro is not defined, ie device does not exist
    • compilation fail becasue driver cannot be registered.

interrupt

• gpio:
  • gpio_pin_configure()
    • init gpio struct for read
  • gpio_init_callback() init cb struct
    • with callback func and pin mask
  • gpio_add_callback() add gpio to callback
  • gpio_pin_interrupt_configure()
    • enable interrupt for gpio struct
• callback func:
  • called with gpio struct + cb struct + pin mask
  • should trigger worker thread
• global thread k_work
  • trigger by k_work_submit
  • k_work.handler stores the actual work
• local thread
  • trigger by semphemore k_sem_give

concurrency

https://docs.zephyrproject.org/latest/reference/kernel/index.html#scheduling-interrupts-and-synchronization

todo

user mode optimization