Programming I/O for Embedded System

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Programming I/O for Embedded System
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Overview

• Basis A DE2 Computer Architecture
• Parallel I/O
• 7-Segment Display Basic
• Manipulating 7-Segment Display on DE2
• Interrupt and Interruption handling
• DE2 Internal Timer Basic
• Manipulating Internal Timer

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Basis A DE2 Computer Architecture

• A SOPC system on DE2 Board
• Created by Quartus II
• With a full featured I/O and memory devices
  integrated

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System components

• NIOS II Processor with on-chip memory
• SDRAM
• Flash Memory
• Internal Timer
• Parallel output ports to 8 green leds and 16 red
  leds
• Parallel output ports to 8 on-board 7-segment
  leds
• On-board LCD output
• Parallel input ports to 16 switches
• Parallel input ports to 4 push-buttons
• JTAG-UART connection to host machine

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Basis A DE2 Computer Architecture

• CPU 32 bits word width, 50 MHz
• On-Chip SRAM 32 bits, 4KB
• On-board SDRAM 16bits, 8MB
• On-board Flash Memory 16 bits, 4MB
• Internal Timer period 1ms
• 3 Parallel I/O ports to LEDs and Switches 8 bits
• 8 Parallel I/O ports to 7-segment LED 8 bits
• On-board LCD Optrex 16207
• JTG UART Serial Communication 64 bits FIFO buffer

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Interrupt request (IRQ)

• Input device generated interrupts
• push buttons IRQ 2
• JTAG_UART IRQ 0
• Internal Timer IRQ 1
• Interrupts provide an asynchronous way for
  data transmission between I/O devices and CPU

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Address Map

• Check sopc configuration for detailed Address map

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Using HAL for embedded software development

• HAL Hardware Abstraction Layer
• A programming interface for embedded system
  development, provide user a hardware-irrevelant
  programming platform
• Parallel I/O Communication
• Device Driver
• Interrupt and DMA control
• Video/Audio signal processing
• Ethernet/Internet access

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Using HAL

• HAL require a bunch of header files be included
  in user C source file, different HAL module
  require different header files
• system.h includes the basic configuration of
  SOPC, Processor parameters, address and data
  bus width, I/O Address Map, should be included if
  HAL is used.

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Parallel I/O

• Parallel I/O is directly connected to processor
  pins, NIOS parallel I/O is addressed in 8-bit,
  and made up by 5 basic port registers
• Data Register
• Direction Register
• Interruptmask Register
• Edge Capture Register
• Outset Register
• Outclear Register

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Parallel I/O Port
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Access to Parallel I/O port in NIOS

• HAL integrated a group of macros and functions
  for I/O port access
• Header file requested
• include system.h
• include "altera_avalon_pio_regs.h

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Access to Parallel I/O port in NIOS

• IORD_ALTERA_AVALON_PIO_DATA(base)
• IOWR_ALTERA_AVALON_PIO_DATA(base,data) 
• // Read and write to I/O Port     
• IORD_ALTERA_AVALON_PIO_DIRECTION(base)  
• IOWR_ALTERA_AVALON_PIO_DIRECTION(base,data) 
• // Set/Get port direction
• IORD_ALTERA_AVALON_PIO_IRQ_MASK(base)
• IOWR_ALTERA_AVALON_PIO_IRQ_MASK(base, data) 
• // Set/Get interrupt mask

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Difference between direct assignment and using
HAL Macro

• We have already seen such code before
• define PIO_ADDR 0x00000010
• .
• ((char )PIO_ADDR)(char) 0xff
• Equivalent code using HAL Macro will be
• define PIO_ADDR 0x00000010
• IOWR_ALTERA_AVALON_PIO_DATA(PIO_ADDR,0xff) 
• Difference? HAL provides a safety way for data
  transmission, user doesnt need to be involved
  into complicated type cast and data alignment.

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Constants definition in system.h

• The constants in SOPC system s.t. I/O port and
  register file address, are defined in system.h.
• For example, user have a 8-bit PIO port named
  switch_0_7 build in SOPC
• The corresponding definition will be added to
  system.h
• define SWITCH_0_7_BASE 0x1803020

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7-segment Display

• Can display hex numbers (0-9,A-F)
• Widely used in digital clock, temperature
  controller,etc

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7-segment Display
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How board segment display works

• Segment display on DE2 board is implemented as
  common-cathode

0x01803080
bit 7 6 5 4 3 2 1 0
X 0 1 1 0 0 0 0
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Connecting segment display to processor

• the 7 pins of segment display can be connected to
  parallel I/O port and use parallel I/O operation
  to control the display on LED.

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C Code Example of Segment Display

• include system.h
• include "altera_avalon_pio_regs.h
• // define SEG_LED_0_ADDR 0x01803080
• // Or use the definition in system.h, which is
  SEG_LED_0_BASE
• main()
• IOWR_ALTERA_AVALON_PIO_DATA(SEG_LED_0_B
  ASE,0x30) 
• //turn segment e and f off

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Push button

• Push button is similar to switch, the difference
  is it need to be hold pressed down to keep the
  value on the parallel I/O port.
• The way to read push button input is the same to
  switch

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Interrupt handling and using internal timer

• Two way for processor to accept external input
• Waiting for input
• Processor will be halting and listening to the
  input port until data is transmitted
• while(data is not updated)
• read data from address of some I/O
  port

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Interrupt handling and using internal timer

• Interrupt
• Data arrival will start an interrupt request to
  processor, when a interrupt is generated,
  processor will stop its current work and turn to
  interrupt service function (data receive), and
  resume work after interrupt is handled.
• interrupt_func()
• transmit data from I/O port to processor
• Main()
• setup interrupt handling function

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Interrupt Request

• interrupt request" (or IRQ) is used to refer to
  either the act of interrupting the bus lines used
  to signal an interrupt, or the interrupt input
  lines on a Programmable Interrupt Controller
• Generated when an I/O event occurs, handled by
  interrupt controller
• Interrupts from different sources are
  differentiated by IRQ line number

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IRQ setting in DE2 Computer
Device IRQ
JTAG_UART 0
Internal Timer 1
Push Button 2
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Interrupt handler function

• NIOS Processer keeps a special address in memory
  ad the entry point for interrupt handler function
• Exception Vector stores the address of interrupt
  handler function, when an IRQ is received by
  processor, it will save the instruction context
  and jump to interrupt handler function.

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How to use interrupt handler

• Enable corresponding IRQ line to processor in
  SOPC builder
• Set I/O devices to enable external interrupt
  generation
• Enable the interruptmask register of
  Parallel I/O
• The ITO bit in internal timer control
  register
• Write interrupt handler function
• Register interrupt handler function

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Code sample for interrupt handler setup

• Include files
• include "system.h"
• include "alt_types.h"
• include "sys/alt_irq.h"
• include "sys/alt_sys_init.h"

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Pseudo-Code sample for interrupt handler setup

• void interrupt_handler()
• main()
• enable system irq
• register handler of irqX as
  interrupt_handler

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Internal Timer

• NIOS Internal Timer
• Works as a stop watch, period register and
  control signals are set by user by programming,
  once started, counter will count down from the
  value in period register to 0 and generate an
  interrupt when time is over.

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Top-level timer diagram
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Timer configuration
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Timer configuration
Configured in SOPC Builder
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Register File for Internal Timer
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Register File for Internal Timer
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Register File for Internal Timer
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How to use internal timer in programming

• Internal timer will loopingly count down from
  value in period register to 0, when counter
  reaches 0, an interrupt on IRQ 1 will generated,
  user need to write IRS function for IRQ 1 to
  capture timer events
• In DE2 Computer, the period of timer is 1 ms,
  means the interrupt will occur 1000 per second

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How to use internal timer in programming

• include "system.h"
• include "alt_types.h"
• include "altera_avalon_timer_regs.h"
• include "altera_avalon_timer.h"
• include "sys/alt_irq.h"
• include "sys/alt_sys_init.h"

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Macros for timer register file access

• IORD_ALTERA_AVALON_TIMER_STATUS(base)
• IOWR_ALTERA_AVALON_TIMER_STATUS(base, data)
• // Read/write to 16 bits status register
• IORD_ALTERA_AVALON_TIMER_CONTROL(base)
• IOWR_ALTERA_AVALON_TIMER_CONTROL(base, data)
• // Read/write to 16 bits control register
• IORD_ALTERA_AVALON_TIMER_PERIODL(base)
• IOWR_ALTERA_AVALON_TIMER_PERIODL(base, data)
• // Read/write to lower 16 bits of period register
• IORD_ALTERA_AVALON_TIMER_PERIODH(base)
• IOWR_ALTERA_AVALON_TIMER_PERIODH(base, data)
• // Read/write to higher 16 bits of period register

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How to use internal timer in programming

• Write user IRS function
• static void Timer_Interrupts(void
  context,alt_u32 id)
• if(Timer_counter gt 1000) / 1S /
• Timer_counter 0 //global
  variable to store reached counter event
• ltUSER CODE HEREgt
• else
• Timer_counter
• IOWR_ALTERA_AVALON_TIMER_STATUS(TIMER_BASE
  , 0x00)//clear status register

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How to use internal timer in programming

• Register IRS
• alt_irq_register(TIMER_IRQ,NULL,Timer_Interrupts)
  
• //Register IRS
• IOWR_ALTERA_AVALON_TIMER_CONTROL(TIMER_BASE,
  0x07)
• //Start timer

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How to capture Timer event in user program

• Keep a global variable for storing information
  from timer events, in main function, check the
  global variable to update timer events
• static int timer_event
• interrupt_handler()
• . //set timer_event
• main()
• register IRS function
• while(timer_event updated)
• user actions

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Summary

• DE2 Computer
• A basic hardware configuration in Quartus for
  embedded system software design
• Parallel I/O
• Basic, register file structure and
  programming
• 7-Segment LED
• Driven by parallel I/O, programming and
  display
• Interrupt handling
• Basic concepts, and how to use in
  programming
• Internal Timer
• Basic, register file structure and
  programming