Designing User Interfaces Spring 1999

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SE 746-NT Embedded Software Systems
Development Robert Oshana Lecture
31 For more information, please
contact NTU Tape Orders NTU Media
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2
Emulation and Debugging Technology for Embedded
Systems Part 1
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Agenda

• Embedded debug philosophy
• Debug kernels
• ROM emulators
• Logic analyzers

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Embedded Debug Philosophy
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Embedded debug Philosophy

• In software development, perhaps the most
  critical, yet least predictable stage in the
  process is debugging
• Many factors come into play when debugging
  software applications
• time is of utmost importance
• The time required to set up and debug a software
  application can have significant impacts on
  time-to-market, meeting customer expectations,
  and financial impact of a well developed product
  that succeeds in the market

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Embedded debug Philosophy

• The integration of an application follows a model
  of multiple spirals through the stages of build,
  load, debug/tune, and change

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Host based debugging

• Certain amount of testing can be done on the PC
• Eventually differences force you to the target
• Potential problems
• Word size
• Byte order

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Storing bytes in 16-bit wide memory introduces
order ambiguity
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Remote debuggers and debug kernels

• Embedded platforms too resource limited and
  specialized to support a full featured debugger
• Embedded systems distribute this function
• Portion resides on target
• Portion resides on host
• Communicate via comm channel (serial, ethernet)

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Typical architecture block diagram
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Debugger control services

• Setting breakpoints
• Loading programs from the host
• Viewing or modifying memory and registers
• Running from an address
• Single stepping the processor

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Resources required from target

• Interrupt vector
• Software interrupt

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Schematic presentation of a debug kernel in a
target system
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Debug kernel

• Similar to an ISR
• Interrupt received from device (such as a serial
  port connected to host)
• Usually set at high enough priority level (NMI?)
  so that debugger is always serviced
• Dont want errant interrupt to disable other
  interrupts (locked out!)

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Debug kernel

• Arrival of interrupt from host stops application
  code
• Processor enters ISR (debug kernel)
• Machine context saved
• Debugger now in control of the target

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How a debugger sets a breakpoint in read/write
memory
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Advantages/disadvantages of a debug kernel

• Advantages
• Low cost 0 to lt 1000
• Same debugger can be used with remote kernel or
  on host
• Provides most of the services that a SW designer
  needs
• Simple serial link is all that is required

• Disadvantages
• Depends on a stable memory subsystem in the
  target and is not suitable for initial HW/SW
  integration
• Not real-time, so system performance will differ
  with a debugger present

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Advantages/disadvantages of a debug kernel

• Advantages
• Can be used with a virtual serial port
• Can be linked with users code for ISRs and field
  service
• Good choice for code development when HW is
  stable
• Can easily be integrated into a design team

• Disadvantages
• Difficulty in running out of ROM-based memory
  because you cant single step or insert
  breakpoints
• Requires that the target has additional services
  which may not be possible
• Might not always have control of the system

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ROM emulator

• Cabling device(s) to match the target system
  mechanical footprint of the target system ROM
  devices
• Fast RAM to substitute for the ROM in the target
  system
• Local control processor
• Comm port to the host
• Additional features such as trace memory and
  flash programming algorithms

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Schematic of a ROM emulator
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ROM emulator

• Allows quick downloading new object images to run
  in the target system
• Change cycle time is important
• ROM emulator with TBase100 ethernet is good for
  downloading large images

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ROM emulator

• ROM emulator is really RAM
• Can set breakpoints in memory
• Gets around the write to ROM problem in your
  embedded system
• Can be used to create virtual ports to the host

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Advantages/disadvantages of a ROM emulator

• Advantages
• Cost effective (1000 - 5000)
• Generic tool, compatible with many different
  memory configurations
• Can download large blocks of code to the target
  system at high speed

• Disadvantages
• Requires that the target system memory is in a
  stable condition
• Feasible only if embedded code is contained in
  standard ROMs rather than custom ASICs or
  microcontrollers with on-chip ROM

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Advantages/disadvantages of a ROM emulator

• Advantages
• Most cost effective way to support large amounts
  of RAM substitution memory
• Can trace ROM code activity in real time
• Provides virtual UART function, eliminating need
  for additional services in target system

• Disadvantages
• Real-time trace is possible only if program
  executes directly out of ROM
• Many targets transfer code to RAM for performance
  reasons

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Advantages/disadvantages of a ROM emulator

• Advantages
• Can be integrated with other HW and SW tools such
  as commercial debuggers
• Can set breakpoints in ROM

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Intrusiveness and RT debugging

• Debug kernel not as useful for trying to find
  real time problems
• Highly intrusive
• Tool presence modifies behavior
• Mechanical compatibility between external tools
  as target system
• Signal intrusion
• Physical intrusion

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Evaluation boards
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SE 746-NT Embedded Software Systems
Development Robert Oshana 10 Minute
Break For more information, please
contact NTU Tape Orders NTU Media
Services [phone]
oshana_at_airmail.net
tapeorders_at_ntu.edu