Linux SVDS BSP

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Linux SVDS BSP

• By Dave Thomas

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Purpose To Port Linux OS to Custom Board

• Boot operating system
• Make hardware available
• Communicate with the board before, during, and
  after OS is booted.
• Perform as much development and communication as
  possible on host PC
• Develop a custom driver specific to our hardware

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Overview of the Hardware

• Board Description
• ARM-based Intel PXA-255
• 64MB Flash Memory
• 10/100 Ethernet
• LCD
• Serial I/O
• FPGA

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Overview of the Hardware
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PXA 255
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Why Linux?

• Rich set of tools
• Very large support community
• Open source is free
• Standard for smart embedded systems
• Sex appeal

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Real-Time Linux

• To digress this is not an express purpose of our
  project
• Linux 2.4 not real-time but
• Kernel can be improved
• Employ a real-time microkernel for hard real-time
• Linux 2.6
• O(1) scheduler provides good soft real-time
• MVL 2.6.10 advertises 65 us maximum preemption
  latency

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Challenges

• Procedural
• Cycle time for testing changes
• Detecting changes made by earlier developers
• Technical
• Network booting
• Understanding the Linux build environment
• Porting a large software project to ARM
• Locating the piece of code

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Methods

• Gentoo embedded Linux distribution
• Produce LOTS of documentation
• Old-fashioned UNIX tools
• diff Naur
• patch p0
• grep -r

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Methods

• Program bootloader firmware and FPGA through JTAG
  interfaces

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Methods

• Logic analysis with Agilent 54622D

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Key Milestones Achieved

• Armboot
• Linux 2.4 kernel and modules
• Network interface
• Boot-from-LAN (kernel and NFS)
• Filesystem
• Toolchain
• X-Windows
• Port to 2.6

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What is a Cross-Toolchain?

• Binutils
• Binutils is a collection of binary utilities,
  including
• ar (for creating, modifying and extracting from
  archives), as (a family of GNU assemblers),
• gprof (for displaying call graph profile data),
• ld (the GNU linker),
• nm (for listing symbols from object files),
• objcopy (for copying and translating object
  files),
• objdump (for displaying information from object
  files),
• ranlib (for generating an index for the contents
  of an archive),
• size (for listing the section sizes of an object
  or archive file),
• strings (for listing printable strings from
  files),
• strip (for discarding symbols), and addr2line
  (for converting addresses to file and line).
  rpm qi binutils
• Static GCC
• C Library
• Final, full GCC

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What is a filesystem?

• All the software for the system that the OS needs
  to boot to a usable system
• UNIX init process
• busybox
• Embedded Linux include
• MontaVista Hard Hat (not Free)
• Familiar.HandHelds.org (for HP iPAQ)
• SnapGear (just came up on our radar)
• emDebian (not ready for mass consumption yet)

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Getting started with gentoo

• Get the experimental stage3 and nfsmount it as
  root filesystem on your target
• For our board its stage3-arm-uclib-softfloat
  (armeb is big-endian)
• On your host,
• Make.conf
• CHOST"armv5l-softfloat-linux-uclibc"
• CTARGET"armv5l-softfloat-linux-uclibc"
• CBUILD"i686-pc-linux-gnu"

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Building a minimal embedded distribution with
gentoo

• Generally
• ROOT/newroot (ex /dev/shm) emerge buildpkg
  ltpkgnamegt
• To build an ultimately minimal filesystem
• ROOT/newroot (ex /dev/shm) INSTALL_MASK"/usr/inc
  lude .a .pl" emerge KO baselayout-lite uclibc
  busybox
• USEminimal emerge --buildpkg xorg-x11

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FPGA

• Field Programmable Gate Array
• Xilinx Spartan2E
• 300K gates
• 100MHz clock (from SDRAM)
• Connected to Variable Latency I/O Interface of
  PXA-255
• Memory mapped access

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PXA255 - FPGA Interface
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Servo Motors

• The Argos pan-tilt head from Mekatronix

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Servo Motors

• The servo positions itself based on the width of
  positive pulses fed to it.
• The rate at which pulses are sent to the servo is
  relatively unimportant. (20 ms period, or 50Hz is
  typical)
• A pulse width of 1.5 milliseconds positions the
  servo at its center, with 1 millisecond and 2
  milliseconds being the accepted limits to either
  side.
• Our servo can move /- 90 degrees

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PWM Linux Driver

• The Linux driver
• Enables access to PWM module
• Hides low level details from the programmer
• Can be built as a module for convenience

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Cameras
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Camera Linux Driver

• Provide access to the camera via the data path
  implemented on the FPGA
• The Linux driver features
• Memory mapped access.
• Hide low level details from the programmer via a
  character device.
• Be built as a module for convenience.

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End product