CS 452/652 Winter 2023 - Lecture 1

Course Overview

• tackle a difficult and sizeable implementation project!
• key characteristics
  • full-stack, including low-level communication
  • timely interaction with real-world system: latency bottleneck
  • robustness against defects (train, switch, sensor)

Software Development

• small kernel
  • no memory translation/protection, no file system
  • micro-kernel with send-receive-reply (SRR) communication
  • multi-threading, no locking → concurrency & non-determinism
  • interrupt handling
• train control
  model and control real-world system in software
  • multi-faceted problem space, inherent timing constraints

System Overview

• train set, Märklin controller, RPi computer, Track PC, TFTP server, development computer (see sketch)
• two-box model: development vs. execution
• example code: freestanding (vs. hosted)
  • no kernel, no libc, no heap
  • explicit linking rules including linker script
  • standard library (newlib) is part of compiler
  • C++ can be used with additional libraries and linking rules

Assignment 0

• assignment is out and due soon → start now
• generic polling loop

  for (;;) {
    if (c1) a1();
    if (c2) a2();
    ...
  }
  

Memory Layout

• at runtime: code, data, no heap, stack
• ELF file format - sections: text, data, bss
  • text and data are placed by boot process
  • entry point is learned by is well-defined
  • bss section must be zeroed by program itself

Build Environment

• linking with libc
• without MMU and/or other magic: SIMD/FP instructions require strict alignmen
  • not a problem, since kernels typically don't do FP
  • but: precompiled libc routines don't care
  • options:
    1. do not use libc!
    2. do not use those routines (see test in Makefile)
    3. recompile libc?
• linking and loading for C++: might need constructors, etc.