Quick example

1
SE 746-NT Embedded Software Systems
Development Robert Oshana Lecture
4 For more information, please
contact NTU Tape Orders NTU Media
Services [phone]
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2
Reference book
3
Reference book
4
Lecture 4

• Hardware fundamentals

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Understand the big picture

• Embedded systems designers will work with many
  different hardware systems
• At first only a general knowledge is required
• Read the Users guide of Programmers Guide
• May not have this for custom H/W

6
Understand the big picture

• What is the overall purpose of the board?
• How does data flow through it?
• May want to create a data flow diagram
• Block diagrams are also helpful
• Refer to it throughout the project

7
DFD for a printer sharing device
ROM (256K)
Serial Port A
computer
Zilog 85230 Serial Controller
Intel 80188EB Processor
Parallel port
Data bus
I/O Bus
printer
Address bus
Serial Port B
computer
RAM (128K)
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Examine the landscape

• Things that the processor can communicate with
• Memories
• Peripherals
• Peripherals specialized hardware devices that
  coordinate interaction with the outside world
  (I/O) or perform a specific hardware function
• Serial ports
• timers

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Examine the landscape

• Address spaces
• Memory space mainly for memory devices
• I/O space reserved for peripherals
• When a peripheral is located within the memory
  space, it is called a memory-mapped device
• Look and act like memory devices (from processor
  point of view)

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Examine the landscape

• Peripherals have specialized functions
• Interpret data as a command to do something
• Data to be processed in some way
• Embedded developers prefer memory mapped
  peripherals
• I/O space can be eliminated (cost)
• Programmer can use pointers, data structures,
  unions to interact with peripherals more easily

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Memory map

• Embedded processors store programs and data in
  memory
• Also in external memory chips
• Located in processors memory space
• Communicate via address/data bus
• Write address on the bus
• transfer data over the bus
• Create a memory map

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Memory map a processors address book
FFFFFh E0000h C0000h 72000h 70000h 20000h
00000h
EPROM (128K)
Flash memory (128K)
Unused
Zilog SCC
Unused
SRAM (128K)
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Header files

• Create a header file that describes the boards
  most important features
• Abstract interface to the hardware
• Can refer to the various locations by name
  instead of address
• Application software more important
• Change affected lines of the board-specific
  header file and recompile

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Header file for Arcom board

• /
• Memory map
• Base address Size Description
• ---------------------------------
• 00000000h 128K SRAM
• 200000000h Unused
• 700000000h Zilog SCC
  Registers
• 700001000h Zilog SCC
  Int. Ack
• 700002000h Unused
• C00000000h 128K Flash
• E00000000h 128K EPROM
• /
• define SRAM_BASE (void ) 0x00000000
• define SCC_BASE (void ) 0x70000000
• define SCC_INTACK (void ) 0x70001000

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I/O map

• Repeat the memory map for the I/O space
• Typically a large part of the I/O space will be
  unused because most of the peripherals there will
  have only a handful of registers

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I/O map a processors address book for
peripherals
Chips that control the parallel port and the
debugger port reside outside the
processor. Ports are used to communicate with
printer and host based debugger
FFFFh FF00h FE00h FD00h FC00h 0000h
Peripheral control block
Unused
Parallel port
Debugger port
Unused
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Header file for I/O peripherals

• /
  
• I/O map
• Base address Description
• ---------------------------------
• 0000h Unused
• FC00h SourceVIEW
  Debugger port
• FD00h Parallel I/O
  Port
• FE00h Unused
• FF00h Peripheral
  Control Block
• 
  /
• define SVIEW_BASE 0xFC00
• define PIO_BASE 0xFD00
• define PCB_BASE 0xFF00

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Learn how to communicate

• Two basic communication techniques
• Polling
• Interrupts
• Processor issues a command to the device by using
  the memory and I/O space
• Then wait for the device to complete the command
• Ask the timer to count down from 1000 to 0

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Polling

• are we there yet?
• Processor repeatedly checks to see if the task
  has been completed
• A large amount of time is spent performing this
  checking
• Wastes a lot of processor cycles

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Polling
Do // play game, read, listen to music,
etc. .. // poll to see if were there
yet status areWeThereYet() while (status
NO)
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Interrupts

• Interrupt is an asynchronous electrical signal
  from a peripheral to the processor
• Processor still issues commands to the processor
• Then waits for an interrupt to signal completion
  of the assigned work
• Free to continue doing other things

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Interrupts

• When interrupt occurs, processor stops what its
  doing and executed a small piece of code called
  an ISR
• Programmer must write the ISR
• Programmer must install it and enable it to be
  executed when the right interrupt occurs
• Interrupts generally decrease the complexity of
  the code and make it more structured

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Interrupts

• Interrupts are used when efficiency is paramount
  or multiple devices must be monitored
  simultaneously
• Polling is used when the processor must respond
  to some event more quickly than is possible using
  interrupts

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Interrupt map

• Each interrupt has an interrupt pin and an ISR
• A mapping must exist between interrupt and ISR
• This is called an interrupt vector table
• Array of pointers to functions
• Processor uses the interrupt type (a unique
  number associated with each interrupt pin) as its
  index into the array

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Interrupt map

• Must initialize the interrupt vector table
  correctly (or the wrong mapping will happen, if
  at all)
• Create an interrupt map that organizes the
  relevant information

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Interrupt map
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• /
  
• Interrupt map
• 
  /
• /
• Zilog 85230 SCC
• /
• define SCC_INT 8
• /
• on-chip timer/counters
• /
• define TIMER0_INT 8
• define TIMER1_INT 18
• define TIMER2_INT 19
• /

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Get to know the processor

• Most processors look and act pretty much the same
  if you are writing in C or C
• Assembly language is a different story
• Look in the databooks

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Processors in general

• Most of the common processors are members of
  families
• Processor
• Microprocessors
• Microcontrollers
• Digital signal processors

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Microprocessor

• Chip that contains a powerful CPU that has not
  been designed with any particular computation in
  mind
• Foundation of personal computers and high-end
  workstations
• Motorola 68K
• 80x86

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Microcontroller

• Similar to a microprocessor
• Designed specifically for use in embedded
  applications
• Contain CPU, small amount of RAM, ROM or both,
  other peripherals on the same integrated circuit
• Reduces cost of embedded systems
• Intel 8051, Motorola 68HCxx

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Digital signal processor

• Specially designed to perform discrete-time
  signal processing calculations
• Audio and video calculations very fast
• Powerful low cost alternative for designers of
  modems and other telecommunications and
  multimedia equipment
• TMS320Cxx and 5600x

33
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