CS452 - Real-Time Programming - Fall 2008

Lecture 25 - Programming Languages for Real-time Programs

Questions & Comments

1. Demos:
   • Tuesday afternoon, starting at 1.00
   • fifteen minutes long
   • only two groups in the lab at a time.

Hardware

First Generation

1. Big mainframe computers
   • transaction processing
   • try to be fast, but it's up to the human to wait
2. Finite state machine controllers
   • real-time
     • machines don't wait
   • primarily focussed on small scale control
     • washing machines
     • transmissions
     • artillery shells
   • usually represented as directed graphs with conditions
     • states are nodes
     • edges are transitions
   • simple translation of mechanical hardware to software
     • discrete components, SSI, with program designed into the circuit
   • run on a fixed clock
     • evaluate conditions
     • change state
   • real-time is put in by hand, painfully
     • could be extensively tested

Second Generation

1. Big mainframe computers
   • transaction processing
   • humans still wait
2. Mini-computers
   • real-time
   • primarily focussed on large scale control
     • chemical plamts
     • trains
     • telecommunications

     always backed up by physical failsafes

   • extremely rudimentary single threaded operating systems, to support
     • polling loops
     • cyclic execution
   • interrupt controllers without operating system support
   • Multiple tasks, when required, were programmed ad hoc using more than one computer
     • communication managed by hand
     • no explicit support for real-time
   • Unix came into being on a minicomputer
     • as a response to the all-singing, all-dancing operating systems of mainframes
     • many Unix-like descendants
   • DEC was the leading manufacturer
     • RT11 (real-time for PDP11) was the operating system it supplied
       • MS-DOS was a rip-off of RT11
       • second generation via Gary Kildall
     • PDP11 used the first fully-integrated CPU.
3. Other tools, such as state charts
   • real-time
   • state machines with states that are Cartesian products
   • focussed on small scale control
     • digital watches
     • traffic lights
   • program was in ROM
     • called firmware
   • cyclic execution

Third Generation

1. Multi-CPU servers
   • more or less tightly coupled
   • dominated by RPC and its relatives
2. Micro-computers
   • many (most?) were used in real-time applications
     • point-of-sale systems
     • games
     • telephone switches
   • supported by DOS (still in use!)
   • much ad hoc intercommunication
     • as with mini-computers
3. Micro-controllers
   • including DSPs

Fourth Generation

1. Multi-(multi-core CPUs) called servers
   • communicate and synchronize using shared memory
     • using techniques from CS343
   • multi-core, cache, and shared memory don't play well together
   • performance limited by threading
     • explicit support for threading, e.g. register windows (Sun) increases performance hugely
     • communication still costly
2. Multi-core microprocessors
   • performance strongly hampered by lack of multi-threading
   • multi-core, cache, and shared memory don't play well together
3. Stream processors
   • good for SIMD

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