stem/IOT/OS/Contiki.md

tags
linux iot

• Linux-based
• Small memory (~20 kB)
• Wide network stacks #net
  • TCP/IP
    • IPv6
  • 6LoWPAN
    • IPv6-based
    • Header compression
  • CoAP
    • Application layer protocol
  • RPL
    • Routing for low power
    • Lossy networks
  • SSL/TLS
  • RIME
    • Own communication solution
• Instant Contiki
  • Dev environment
  • Whole VM

Functional

• Separates basic system from dynamically loadable and programmable services
  • Processes
• Event-driven kernel
  • Multi-threading supported by library
  • Hybrid OS
  • No hardware abstractions
• Services communicate by posting kernel events
• Refer to stack with pointer to process state
  • Each service has state in private memory space

Process

• Cooperative
  • Code running sequentially with respect to other coop code
• Pre-emptive
  • Temporarily stops cooperative code
• Normal processes run cooperatively
  • Interrupts and real-time timers run pre-emptively
    • Higher priority
• Programs are processes
  • Started on boot
  • When module containing process loaded
• Processes run on timer firing or external events

Timers

• Libraries
  • Used by applications and system
• Check for timer completion
• Waking system from low power
• Real-time task scheduling
• Allows cooperation when threads sleep
  • Low power mode
• timer and stimer
  • Simplest
  • See if time period passed
  • Need querying
• etimer
  • Event timers
  • Scheduling
  • Uses clock time from clock module
  • struct etimer

Clock

• System time starts from zero when the Contiki system starts
• clock_time()
  • In ticks
• clock_seconds()
  • In seconds
• CLOCK_SECOND
  • Ticks per second

Power Saving Mode

• Kernel does not provide any power saving abstractions
• Need to implement in application
• To help an application decide when to power down the system
  • The event scheduler exposes the size of event queue
  • If there were not events scheduled, this information can be used to power down the processor