Characteristics of Realtime and Embedded Systems

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Characteristics of Realtime and Embedded Systems

• Chapter 1

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Embedded Systems

• Embedded systems are computing systems with
  tightly coupled hardware and software
  integration.
• Designed to perform dedicated function
• Embedded means that the system is a integral part
  of a larger system
• Multiple embedded systems can co-exist in a
  single system.
• General purpose processor are typically not aware
  of the applications.
• An embedded processor is application-aware.

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Embedded Systems (contd.)

• Hardware and software co-design hardware and
  software for the embedded system are developed in
  parallel.
• Cross-platform development Both embedded system
  and its application use the cross-platform
  development method.
• Software is developed on one platform but runs on
  another.
• Software storage will have to be chosen to allow
  for upgradeability.
• Of course, the SoC, PoE, etc.

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Realtime Systems
Real-time systems
Synchronous Asynchronous Outputs
Synchronous asynchronous Events
Timing constraints
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Real-time Systems

• Real-time systems are those systems in which the
  overall correctness of the system depends on both
  the functional correctness and the timing
  correctness.
• Realtime systems also have a substantial
  knowledge of the system it controls and the
  applications running on it.
• Deadline dependent.
• Predictability is important.

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Hard and soft Real-time Systems

• A hard real-time systems is a real-time system
  that must meet its deadlines with a near zero
  degree of flexibility. Deadlines must be met,
  otherwise catastrophes occur.
• A soft-time system is a real-time system that
  must its deadlines but with a degree of
  flexibility. The deadlines contains various
  levels of tolerance, even statistical
  distribution of response times with different
  degrees of acceptability.
• An important requirement scheduling algorithms

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Real-time Embedded Systems
RTS
EMB
RTEMB
Railway monitoring and scheduling RTS Cell
phone EMB Heart pacemaker RTSEMB
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Chapter 2 Basics of Development for Embedded
Systems

• Typical cross-platform development environment
• Host system essential tools are cross compiler,
  linker, source level debugger
• Executable image contains RTOS, Kernel,
  application program compiled and linked
• Target system where to store the executable
  image, and how?
• Connections ethernet and serial
• See figure 2.1

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Making of an Executable

• Makefile
• Demo

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Compile and Link

• Compiler converts the high level language code
  into native machine code or object code
• Linker does symbol resolution and symbol
  relocation to generate the executable code
• See Figure 2.3
• Symbol resolution is the process by which the
  linked goes through each object file and
  determines where the external symbols in it are
  located. Then it copies the required file into
  the final image.
• Symbol relocation is the process in which the
  linker maps symbol reference to its definition.

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ELF (Executable Linker Format)

• An object file contains
• file size, binary code, data size, source file
  name and other general information
• Machine architecture specific binary instructions
  and data
• Symbol table and relocation table
• Debug information, which the debugger uses
• There are standards for organizing object file
  formats. ELF is very commonly used format.

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ELF (contd.)

• Compiler organizes the compiled code into
  system-defined as well as user-defined content
  groupings called sections.
• Example sections binary code, symbol table
• Each section also has important information about
  load address and run address.
• Section header and program header Listing 2.1
• A section header table is an array of section
  header sections of an object file.
• A program header table is array of program header
  structures describing a loadable segment of an
  image.

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Section Types (sh_types)

• PROGBITS code or initialized data
• SYMTAB etc.
• Some common system created default sections are
  .text, .data, .sdata
• Section attributes (sh_flags) WRITE, ALLOC,
  EXECINSTR
• sh_addr is the section address and p_addr is the
  program address on the target machine

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User defined sections

• You could add user-defined sections
• .section mysection
• If you were to create the embedded program from
  scratch you will define it in terms of sections
  as defined above.
• Remember the .data and .text sections from your
  MIPS code (of cse341).

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Mapping Executable Images into Target Embedded
Systems

• Multiple source files (C/C, assemble) have been
  compiled and assembled into object files, a
  linker must combine these object files and merge
  sections from different object files into program
  segments.
• The process creates a single executable image for
  the target embedded system.
• Embedded system developer uses linker directives
  to control how the linker combines sections and
  allocates segments into target system.
• Common directives are MEMORY and SECTION (see
  examples Listing 2.2 and 2.3)

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Memory Map of the Target System

• See fig 2.5 and compare it with MEMORY directive
  listing 2.2
• Also check out the memory map of XINU
• Section .text can be mapped to ROM, Flash or Ram
  where the section .data has to be mapped to RAM.

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Generating Executable Image

• Combining multiple sections into executable
  image fig. 2.6
• Mapping executable image into target memory fig
  2.7
• Module upgradability through flash memory.
• Use SDRAM for code /data that require fast access
  and DRAM for the rest of the code/data.
• See Listing 2.5 and Figure 2.8 for examples.