CS 452/652 Spring 2022 - Lecture 1

May 3, 2022 next

purpose: 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)

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

train set, controller, ARM computer, Track PC, TFTP server, development computer
see sketch
development
- two-box model: development vs. execution
- manual linking and loading
- gcc/g++ with basic library support → freestanding: no heap
- rudimentary gdb support
- example code provided

a lot of C functionality comes from the C standard libray
C standard library interfaces with operating system
here: newlib, but no operating system kernel
- limited functionality - no heap!
using newlib routines that always need dynamic memory → not possible
using newlib routines that might need dynamic memory → might be possible
- if certain that heap-needing functionality not triggered
- linker might still want to resolve heap-related program break symbol → fake it!

generic polling loop

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

TS-7200 RAM

0x2000000 high end of 32 MB RAM
0x0218000 historic Linux load/start address
0x0100000 suggested load address
0x0044F88 lowest possible load address
0x0000000 low end of RAM
at runtime: code, data, no heap, stack
ELF file format - sections: text, data, bss
- text and data are placed by RedBoot 'load' command
- entry point is learned by RedBoot for 'go' command
- bss section must be zeroed by program itself
- RedBoot 'go' does not re-initialize the data section

0x2000000	high end of 32 MB RAM
0x0218000	historic Linux load/start address
0x0100000	suggested load address
0x0044F88	lowest possible load address
0x0000000	low end of RAM