ECEN 4623/5623RT Embedded Systems

Mid-Term Review Lecture

MT Review

• Fundamentals of RT Analysis– RT Correctness – Before Deadline and Correct Result– Best Effort, Hard RT, Isochronal RT, and Soft RT– Utility Curves for each of the above– CPU, I/O, and memory resource space (CPU-bound, I/O-bound,

memory/CPU trade-offs)– Basic Timing Diagrams– Theorem 1 – RM Least Upper Bound– Theorem 2 (Lehoczky, Shah, Ding) – If deadline(s) are met over

longest period from C.I., then system is feasible– Fixed priority, preemptive, run-to-completion scheduling– Services and interference (interrupts and higher prio services)– Necessary and Sufficient feasibility means?

MT Review

• Deadline Monotonic Theory– DM priority assignment policy

– Simple sufficient feasibility test

– Improved (more necessary) feasibility test

– Differences between RM and DM theory• T not equal to D

• Priority assignment policy

• Iterative feasibility test

MT Review

• Rate Monotonic Theory– RM priority assignment policy (optimality is ?)– Liu and Layland Assumptions

• C = WCET• T=D• Critical Instant• Others?

– RM Feasibility test is ?– Derivation of 2 task RM sufficient LUB

• LUB is O(C) complexity – equation• Sufficient, but not Necessary and Sufficient

• Dynamic Priority Theories– EDF– Least Laxity

MT Review

• Tornado / VxWorks– Diagram of Host-Target IDE– Cross compilation– Target agent (WDB)– Target server (tgtsvr)– Target-Host communication (ethernet, serial, JTAG/BDM)– Dynamic linking and loading

• Downloadable ELF modules• Module manager, loader/unloader• built-in target symbol table?• Host-based symbol table?• Host-and-target symbol table with synchronization?

– logMsg versus printf• Printf I/O delays caller and can’t be called in kernel/ISR context• logMsg performs output in slack time via tlogTask and message

queue interface

MT Review

Interval timer

Host Link

X-window system

Target server

Windview

Target agent

WindKernel

X-interfaceControl Callback {time-stamp read}

Link Data Relay

WTX-App-Cmd

WTX-DataWTX-Cmd

WTX-App-Data {wvOn, wvOff}

WDB-CmdWDB-Data

Trace-data

{time-stamp}X-display

update

Target Link

MT Review

• RT Synchronization– Priority Inversion– Unbounded Priority Inversion– Priority Inheritence– Priority Ceiling– Necessary 3 Conditions for Unbounded Prio Inversion

• 3 or more tasks (H, M, L priority)• H and L tasks involved in mutex• 1 or more M tasks not involved in mutex cause interference

– Mars Pathfinder Story• What went wrong?• Why?• How was it fixed?

MT Review

• VxWorks Kernel Mechanisms– Basic Task Control – taskLib

• VxWorks task states (see Programmer’s Guide)• Creation, Deletion, and Control

– Basic Synchronization – semLib– POSIX RT Extensions

• Message queues– Priority enqueue and dequeue– Same priority?– Blocking vs. non-blocking send and receive

• Real-time signals– Signals that queue – why?– Passing data – how?

• Real-Time interval timers and clocks– Systems tick and interval timer jiffy– Hardware interval timer operation– Virtual timers built on hardware interval timer(s)

MT Review

• Estimating and Measuring C (WCET)– Windview analysis

• Kernel instrumentation (store event ID and time-tag in trace buffer at key locations – e.g. context switch)

• Dump trace-buffer in slack time to host• Post-analyze

– Estimating C on RISC architectures• Pipelining and superscalar processing• CPI• Cache hit/miss ratio (I-cache and D-cache)• Pipeline stalls• Page faults

– WCET