CS 3210 Design of Operating Systems
College of Computing, Georgia Tech

Thursday 13 January 2000

Kernel Overview / Architecture / Development with Skiff Boards

announcements

• roll
• photos
• handouts: LCKC chs 1-3, Beck Ch 3?
• team signups
• books
• new web pages

review of code development with Skiff boards

• Skiff Lab
• Home development
• power
• console (db9 serial)
• ethernet (hub or cross-over cable)
• flash rom, ram

Skiff development: software components

• terminal emulator: 38400, 8-1-N, no flow control
  • Linux: minicom
  • Windows/NT: hyperterminal
  • xmodem for serial download (only hyperterminal xmodem works ... ouch!)
• kernel source tree (~50meg)
• Linux Intel hosted gcc cross-compiler (~100meg)
  • xmodem download (slow, about 20 minutes)
  • ethernet flash write (fw)
• bootloader (in flash)
• remotely mounted filesystems (NFS)
  • to access additional cross-compiled applications, libraries, etc.
  • for transferring applications to Skiff board
  • to access new kernel when using fw
  • for building root filesystem
• ramdisk-based root filesystem (initrd)
  • stored in flash
  • reconstituted as part of boot process

kernel architecture overview (Maxwell Ch 3)

• design goals (lots of tradeoffs)
  • clarity (within constraints of robustness, speed)
  • compatibility
    • POSIX, Sys V, BSD, "personalities", emulation
    • file systems, networking, device drivers
    • mechanism: modularity, abstraction, interfaces (e.g. VFS)
  • portability
  • robustness
  • security
  • speed
• basic architecture:
  • hardware
  • kernel (arch dependent, independent)
  • system calls
  • libraries
  • applications
• kernel structuring techniques
  • layering
  • modules
  • objects
  • Linux is hybrid, based on pragmatic decisions
• monolithic kernel vs. microkernel
  • speed vs. flexibility, maintainability
• kernel "module" system
• kernel source structure (usually /usr/src/linux)
  • Documentation
  • arch/ (alpha, arm, i386, m68k, mips, ppc, sparc, sparc64, etc.)
    • boot code, interrupts, trap handling, fp emulation, optimized utility routines (strlen)
    • contains kernel subdirectories for platform-specific kernel stuff
    • contains mm subdirectories for platform-specific memory stuff
  • drivers
  • fs (vfs, ext2, isofs, proc, etc.)
  • include (for compiling the kernel; not stdlib includes for apps)
  • init -- main.c (!), boot, kernel initialization, some tricks here
  • ipc
  • kernel -- platform-independent core stuff; sched.c, fork.c, etc.
  • lib -- inflate.c, stdlib utilities for use within the kernel
  • mm -- platform-independent memory stuff
  • net
  • scripts -- kernel compilation, configuration scripts

readings for next tuesday (18 jan 2000)

• Maxwell Ch 2 "First Look at Code" printk
• Maxwell Ch 4 Booting
• Beck Ch 3.2.3, Appendix D Booting
• Rubini Ch 16 Kernel Source Tour, Booting

coming up!

• system calls
• timers, interrupt handling
• char device drivers ? project
• process/thread structure
• scheduling