Software Development and Software Loading in Embedded Systems

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Software Development and Software Loading in
Embedded Systems
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Cross Compilation

• Development of embedded software is not generally
  done on the target processor
• - Software development is done on a host
• The compiler may run on one kind of processor
  (80x86) produce code for another ( 8051)
• This is called a cross-compiler, but is otherwise
  not unlike any other compiler.

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The Build and Load Process of Embedded
Application Programs
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Linking and Locating

• After compilation of modules, a set of object
  files must be linked together
• - The linker runs on the host and does this
• - The output is a relocatable program, with
  no fixed
• addresses yet assigned to the code/data
• A separate relocation step must be performed to
  create the executable binary image
• - general-purpose computers generally do
  this
• automatically, as the relocatable is
  loaded

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Linking
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Locating
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Startup Code

• Embedded software generally runs out of ROM, with
  all the modules linked together
• - It is itself responsible for
  booting/initializing the system
• In addition to your application code, it is
  necessary to have code to prepare the CPU for the
  execution of your C/C application.

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C/C Startup Code Details

• Copy initialized data from ROM to RAM
• Zero uninitialized data area
• Allocate space for and initialize the stack
• Initialize the processors stack pointer
• Create and initialize the heap (optional)
• Execute constructors and initializers for all
  global variables (C only)
• Enable interrupts
• Call main()

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Reset Vector

• When a processor is started or reset, it must
  read its first instruction from a fixed known
  address
• - A small piece of reset code is stored at
  that
• address typically in a nonvolatile memory
  device
• The reset code might just disable interrupts
  (since the vector table isnt initialized yet)
  and jump to the startup code
• - Though sometimes additional hardware
  initialization is
• required before the startup code can get
  control

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The World Before main()

• Reset code (assembly, at known address in ROM)
• Hardware intialization (assembly, in ROM)
• Startup code (assembly, in ROM)
• C/C program (starting from main)