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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Exam Tuesday

• I will try to print any manuals that you will
  need
• You will not need a calculator
• Binary, Hex
• Basic Assembly Code
• Arithmetic
• Load and Store
• Branching
• C Code
• Rounding
• Interpolation
• Pointers
• Structures
• C Pre-processor

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• NO DIV instruction

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Using Registers

• DivStart enter with numbers in r0 r1
• mov r2,1 bit to control the division
• Div1 cmp r1,0x80000000 shift r1 left till MSB
  set
• cmpcc r1,r0 ...or r1gtr0
• movcc r1,r1,LSL1 shift r1 left if require
• movcc r2,r2,LSL1 shift r2 left if r1
  shifted
• bcc Div1 repeat whilst more required
• mov r3,0 zero r3
• Div2 cmp r0,r1 test for possible
  subtraction subcs r0,r0,r1 subtract if r0gtr1
• addcs r3,r3,r2 put relevant bit into
  result movs r2,r2,LSR1 shift control bit
• movne r1,r1,LSR1 halve unless finished
• bne Div2 loop if there is more to do
  divide result in r3 Remainder in r0
• mov r1,r3 result (r0/r1) now in
  r1 mov r15,r14 return from subroutine

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USART

• USART10xFFFC0000
• USART20xFFFC4000

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Lines
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Transmit a Character
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User Concerns

• Both devices must be configured similarly
• Baud rate
• Data length
• Stop Bits
• Start Bits
• Handshaking
• Hardware handles the details
• Often, three wires are used
• RX
• TX
• GND
• DB9 (2, 3, 5)
• NULL MODEM
• Transmit and receive lines are swapped

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Configuration and Control

• PMC- for clock
• AIC- for interrupts
• US_CR Control register
• Reset-transmit, receive and status
• Enable/disable- transmit and receive
• DTR and RTS control
• Start and Stop Breaks

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Mode Register US_MR

• Clock to SCK?
• Over sampling mode 8x or 16x
• ACK enable, disable (some protocols)
• Max iteration (some protocols)
• Filter ON/OFF (infrared)
• Manchester ON/OFF
• Delimiter One Bit or Frame

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US_IER US_IDR Interrupt Enable/Disable

• AIC accepts interrupts or not
• US_IER US_IDR sets causes

One char at at time
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US_IMR Interrupt mask register

• Lets software know which event caused interrupt

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US_CSR Channel Status Register

• CTS and DSR
• New character arrived?
• Transmitter empty?
• Receiver ready?

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US_THR US_RHRHolding Registers

• Data received
• Data to be sent

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US_BRGR Baud rate generator register

• Divides clock by some amount

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Other registers

• US_TOR time out register
• US_TTR time guard register
• US_FIDI FI over DI ratio ??
• US_NER Number of errors
• US_MAN Manchester encoding
• US_IF filter control

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Code Structure

• With or without interrupts
• Configure PIO controllers to peripheral
• Enable clock via PMC
• Configure USART
• Disable interrupts
• Reset receiver and transmitter
• Define the baud rate divisor register
• Write the Timeguard Register (for slow devices)
• Clear Transmit and Receive Counters
• Define the USART mode
• Enable USART US_CR
• IF interrupts
• Select Interrupts to Enable on the US_IER
• Configure Interrupts on the AIC
• Enable Interrupts on the AIC
• NOTE must have ISR in place to handle interrupt

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Typical Interrupt Service Routine

• Check to see what caused it
• Do what only what is necessary
• Clear condition
• Return

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• __ramfunc void Usart_c_irq_handler(void)
• AT91PS_USART USART_pt AT91C_BASE_US0
• unsigned int status
• status USART_pt-gtUS_CSR // get Usart status
  register
• if ( status AT91C_US_RXRDY)// Get byte and
  send
• AT91F_US_PutChar (USART_pt,
  AT91F_US_GetChar(USART_pt))
• if ( status AT91C_US_OVRE) // clear
  US_RXRDY
• AT91F_US_GetChar(USART_pt)
• AT91F_US_PutChar (USART_pt, 'O')
• if ( status AT91C_US_PARE) // Check parity
  error
• AT91F_US_PutChar (USART_pt, 'P')
• if ( status AT91C_US_FRAME) //
  check frame error
• AT91F_US_PutChar (USART_pt, 'F')