EECE 631 Microcomputer System Design Lecture 9 Programming for Microcontrollers

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EECE 631Microcomputer System DesignLecture 9
Programming for Microcontrollers

• Spring 2008
• Chris Lewis
• clewis_at_ksu.edu

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Help for the Lab

• 2D Table interpolation
• How can you interpolate between two values?
• 3 times for a single entry
• Example Compass Calibration table
• Every 10 degrees of heading
• Every 5 degrees of tilt -45
• Compute heading for 33 degrees with 11 degrees of
  tilt
• 30, 10 gt 3
• 30, 15 gt 5
• 40, 10 gt -1
• 40, 15 gt -15

C1
Value
C2
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Overview of Features in Processor

• 32 Bit and 16 Bit Thumb instruction sets
• High Speed Flash
• High Speed SRAM
• Memory Controller (external memory?)
• Periodic Interval Timer
• Watch Dog Timer
• 32 Bit Real-time Timer
• Parallel I/O (how many bits?)
• USB support
• Synchronous Serial Controller
• 2 USART
• SPI
• 16Bit Timer Counter
• 4 Channel 16bit PWM controller
• Two Wire Interface
• 10 Bit 8 Channel A2D
• 5Volt Tolerant I/O
• 3.3 Volt Operation

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Example using hardware, Running Lights

• include "Board.h
• / Global variables /
• define SPEED (MCKKHz/10)
• unsigned int LedSpeed SPEED 50
• const int led_mask8 LED1, LED2, L ED3, LED4
• void change_speed ( void )
• // Begin
• if ( (AT91F_PIO_GetInput(AT91C_BASE_PIOA)
  SW1_MASK) 0 )
• if ( LedSpeed gt SPEED ) LedSpeed -SPEED
  
• if ( (AT91F_PIO_GetInput(AT91C_BASE_PIOA)
  SW3_MASK) 0 )
• if ( LedSpeed lt MCK ) LedSpeed SPEED
• // End
• void wait ( void )
• // Begin
• unsigned int waiting_time
• change_speed ()
• for(waiting_time 0 waiting_time lt
  LedSpeed waiting_time)

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int main() // Begin int i // First,
enable the clock of the PIO
AT91F_PMC_EnablePeriphClock ( AT91C_BASE_PMC, 1
ltlt AT91C_ID_PIOA ) // then, we configure
the PIO Lines corresponding to LED1 to LED4
// to be outputs. No need to set these pins to be
driven by the PIO because it is GPIO pins only.
AT91F_PIO_CfgOutput( AT91C_BASE_PIOA,
LED_MASK ) // Clear the LED's. apply a "1"
to turn off LEDs AT91F_PIO_SetOutput(
AT91C_BASE_PIOA, LED_MASK )
__enable_interrupt() \\ intrinsic function
// Loop forever for () // Once
a Shot on each led for ( i0 i lt NB_LEB i
) AT91F_PIO_ClearOutput( AT91C_BASE_PIOA,
led_maski) wait()
AT91F_PIO_SetOutput( AT91C_BASE_PIOA, led_maski
) wait() // End for //
Once a Shot on each led for (
i(NB_LEB-1) i gt 0 i-- )
AT91F_PIO_ClearOutput( AT91C_BASE_PIOA,
led_maski) wait()
AT91F_PIO_SetOutput( AT91C_BASE_PIOA, led_maski
) wait() // End for //
End
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Procedure for Using Peripheral

• Configuration Register
• Pin Assignment Register
• Data Registers

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Resources and Dependencies
Clocks, Pins, and Interrupts
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Peripheral Register Mapping
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Each Bit has defined Meaning
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Embedded C Issues

• Set and clear bits of specific bits in memory
  mapped registers
• Example from First Lab
• //-----------------------------------------------
  -----------------------------
• // \fn AT91F_PIO_SetOutput
• // \brief Set to 1 output PIO
• //-----------------------------------------------
  -----------------------------
• __inline void AT91F_PIO_SetOutput(
• AT91PS_PIO pPio, // \arg pointer to a PIO
  controller
• unsigned int flag) // \arg output to be set
• pPio-gtPIO_SODR flag
• //-----------------------------------------------
  -----------------------------
• // \fn AT91F_PIO_ClearOutput
• // \brief Set to 0 output PIO
• //-----------------------------------------------
  -----------------------------
• __inline void AT91F_PIO_ClearOutput(

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Call from Main

• // Once a Shot on each led
• for ( i0 i lt NB_LEB i )
• AT91F_PIO_ClearOutput(AT91C_BASE_PIOA,
  led_maski)
• wait()
• AT91F_PIO_SetOutput( AT91C_BASE_PIOA,
  led_maski )
• wait()
• // End for
• AT91C_BASE_PIOA Must be defined in include
  Board.h
• Board.h includes another file include
  AT91SAM7S256.h
• define AT91C_BASE_PIOA ((AT91PS_PIO)
  0xFFFFF400) // (PIOA) Address

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Structure Definition

• typedef volatile unsigned int AT91_REG//
  Hardware register definition
• typedef struct _AT91S_PIO
• AT91_REG PIO_PER // PIO Enable Register
• AT91_REG PIO_PDR // PIO Disable Register
• AT91_REG PIO_PSR // PIO Status Register
• AT91_REG Reserved01 //
• AT91_REG PIO_OER // Output Enable Register
• AT91_REG PIO_ODR // Output Disable Registerr
• AT91_REG PIO_OSR // Output Status Register
• AT91_REG Reserved11 //
• AT91_REG PIO_IFER // Input Filter Enable
  Register
• AT91_REG PIO_IFDR // Input Filter Disable
  Register
• AT91_REG PIO_IFSR // Input Filter Status
  Register
• AT91_REG Reserved21 //
• AT91_REG PIO_SODR // Set Output Data Register
• AT91_REG PIO_CODR // Clear Output Data
  Register
• AT91_REG PIO_ODSR // Output Data Status
  Register
• AT91_REG PIO_PDSR // Pin Data Status Register

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Embedded C Techniques

• Pointer to Structure overlaid on top of memory
  mapped peripherals control and data register
• Bit Setting and clearing (from Board.h)
• define LED1 (1ltlt0) / PA0 / PGMEN0
  PWM0 TIOA0 48 /
• define LED2 (1ltlt1) / PA1 / PGMEN1
  PWM1 TIOB0 47 /
• define LED3 (1ltlt2) / PA2
  PWM2 SCK0 44 /
• define LED4 (1ltlt3) / PA3
  TWD NPCS3 43 /
• Use
• Ptr-gtdata_register LED3 // set bit
• Ptr-gtdata_register LED2 // clear bit

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Bit Manipulation

• NOT ! -vs-
• AND -vs-
• OR -vs
• Shift ltlt and gtgt

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Using Digital IO

• PIOA Parallel I/O Module
• Product Dependencies
• Power Management
• Advanced Interrupt Controller
• Programming Interface
• Configure PMC to enable clock
• Configure AIC if needed
• Assign Pins to PIO
• Configure as either IN or OUT
• Write 1s to Set Register to Set
• Write 1s to Clear Register to Clear
• Read Status Register to read