EE382C Embedded Software Systems
Specification and Description Language

Announcements

• TBA

Lecture

• Lecture on Specification and Description Language in PowerPoint and PDF formats
  • SDL assumes a sloppy distributed system model
    • Channels have nondeterministic communication delays (e.g. from network routers)
    • Signals have zero delay that is "software" delay on the same processor, and not a network delay
  • SDL accesses time information in three ways (from Prof. Stephen A. Edwards, Columbia University)
    • First, the input queues on each process respect the arrival order unless explicitly overridden using a "save" operator, so a sequence of events sent from one process to another arrive in a coherent order.
    • Second, an SDL process has access to global time through the "now" operator, which returns a system-wide wall clock time.
    • Third, SDL processes may employ timers that automatically generate events after a prescribed timeout period.
  • Data sent over channels does not appear to have timestamps, and the relative timing of processes within the same block appears to be limited to simple causality; races are explicitly permitted. (from Prof. Stephen A. Edwards, Columbia University)