3Software Design Basics in Embedded Systems

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3-Software Design Basics in Embedded Systems
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Development Environment

• Development processor
• The processor on which we write and debug our
  programs
• Usually a PC
• Target processor
• The processor that the program will run on in our
  embedded system
• Often different from the development processor

Development processor
Target processor
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Development Environment

• Compilers
• Cross compiler
• Runs on one processor, but generates code for
  another
• Assemblers
• Linkers
• Debuggers
• Profilers

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Running a Program

• If development processor is different than
  target, how can we run our compiled code? Two
  options
• Download to target processor
• Simulate
• Simulation
• One method Hardware description language
• But slow, not always available
• Another method Instruction set simulator (ISS)
• Runs on development processor, but executes
  instructions of target processor

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Instruction Set Simulator For A Simple Processor
include ltstdio.hgt typedef struct unsigned
char first_byte, second_byte
instruction instruction program1024
//instruction memory unsigned char memory256
//data memory void run_program(int num_bytes)
int pc -1 unsigned char reg16, fb,
sb while( pc lt (num_bytes / 2) )
fb programpc.first_byte sb
programpc.second_byte switch( fb gtgt 4 )
case 0 regfb 0x0f memorysb
break case 1 memorysb regfb
0x0f break case 2 memoryregfb
0x0f regsb gtgt 4 break
case 3 regfb 0x0f sb break
case 4 regfb 0x0f regsb gtgt 4
break case 5 regfb 0x0f - regsb
gtgt 4 break case 6 pc sb break
default return 1
return 0 int main(int argc, char
argv) FILE ifs If( argc ! 2
(ifs fopen(argv1, rb) NULL )
return 1 if (run_program(fread(pr
ogram, sizeof(program) 0)
print_memory_contents() return(0)
else return(-1)
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Testing and Debugging

• ISS
• Gives us control over time set breakpoints,
  look at register values, set values, step-by-step
  execution, ...
• But, doesnt interact with real environment
• Download to board
• Use device programmer
• Runs in real environment, but not controllable
• Compromise emulator
• Runs in real environment, at speed or near
• Supports some controllability from the PC

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Quartus II Development Tool
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Example of File Menu
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New Project Wizard
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Creation of new project
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Adding files to project
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Choose device family and specific device
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Electronic Design Automation Tools
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Summary of project settings
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Quartus II display of created project
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ProcessinggtStart Compilation
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Assignment gt Pins
For example, SW0,SW1 are connected on FPGA Pins
N25,N26. LEDG0 is pin AE22.
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Available pins
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Programming the FPGAToolsgtProgrammer

• Check the Program/Configure box, then click
  Start.
• Wait till the progress bar show 100 (done).

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Chapter Summary

• General-purpose processors
• Good performance, low NRE, flexible
• Controller, data-path, and memory
• Structured languages prevail
• But some assembly level programming still
  necessary
• Many tools available
• Including instruction-set simulators, and
  in-circuit emulators
• ASIPs
• Microcontrollers, DSPs, network processors, more
  customized ASIPs
• Choosing among processors is an important step
• Designing a general-purpose processor is
  conceptually the same as designing a
  single-purpose processor