IO and Peripherals

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I/O and Peripherals
Key Concepts and Terms

• control and status registers
• ports
• bitmasking
• bit manipulation
• device drivers
• memory mapped I/O
• bandwidth
• synchronization
• polling
• busy waiting

• serial and parallel interfaces
• analog and digital signals
• analog to digital conversion
• sampling frequency
• active high, active low
• edge-triggered
• level triggered
• timing diagram

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I/O and UM003

• I/O
• Ports
• Device Drivers and Interfaces
• Control and Status Registers
• Synchronization Techniques
• Signal Processing
• Signal Types
• Sampling
• A/D Conversion

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UM003 Robot (Motor) Controller
encoder count (est pos)
AtMega (PD Control)
Motor
Encoder
user command (ref pos)
Serial Comm
PWM signal (motor control)
task goal (ref pos)
Visual System
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UM003 Motor Control
encoder count (est pos)
/3
/3
Motor
dir
Ch. A
Ch. B
PWM
dir
Motor
PWM
Ch. A
Ch. B
dir
PWM
Motor
Ch. A
Ch. B
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(No Transcript)
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Control and Status Registers

• Initialization
• direction
• function
• synchronization (when to read or write)
• Interaction with peripheral
• read or write value

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PORTS

• Atmega datasheet p. 365
• PORTA 1B (3B)
• DDRA 1A (3A)
• PINA 19 (39)
• winAVR io128.h (IO for atmega128)
• / Input Pins, Port A /
• define PINA _SFR_IO8(0x19)
• / Data Direction Register, Port A /
• define DDRA _SFR_IO8(0x1A)
• / Data Register, Port A /
• define PORTA _SFR_IO8(0x1B)
• winAVR sfr_defs.h (special function register
  defs)
• define _SFR_IO8(io_addr) ((io_addr)
  __SFR_OFFSET)

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Read / Write to Ports

• Memory-Mapped I/O
• Port-Mapped I/O
• DMA

out(PORTA, 0x33) or PORTA 0x33
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Bit Manipulation


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Control Status Register Pins/Ports
iom128.h / Port B Data Register - PORTB
/ define PB7 7 define PB6
6 set bit7, bit6, bit0 hi (equivalent to
0xC2) DDRB (1ltltPB7) (1ltltPB6) (1ltltPB0)
read 4 most significant bits data PINA 0xF0
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UM003 Motor Control
encoder count (est pos)
/3
/3
Motor
dir
Ch. A
Ch. B
PWM
dir
Motor
PWM
Ch. A
Ch. B
dir
PWM
Motor
Ch. A
Ch. B
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Decoder (motor position)
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Reading Decoder on UM003

• int32_t read_decoder_U7()
• // select the appropriate decoder (U6/U7/U8)
• PORTG 0x
• //need to wait for a moment to ensure the demux
  has switched
• delay_ms(10)
• //read the data from the decoder and do
  something with it
• int8_t data PINC
• //now to reset the encoder
• PORTG 0x
• delay_ms(10)
• //and lastly, turn the encoder back on (stop
  reset)
• PORTG 0x00

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Device Driver

• Goal Hide the hardware completely.
• ONLY module to read/write control status
  registers directly.
• BUT, in embedded systems, little distinction
  between
• application software, OS, and device drivers
• The making of a device driver
• Create interface to registers (.h file)
• Define variables to track status.
• Routine to initialize hardware.
• API for users
• Interrupt service routines.
• First use polling to get driver working.

Writing Windows CE Device Drivers Principle to
Practice, Linux device driver design
embedded.com
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Relating to the outside world

• 4 categories of interfaces
• parallel (digital, simultaneous bits at a time)
• serial (digital, one bit at a time)
• analog (voltage, continuum)
• time (analog period, frequency, )
• Types of Signals (signal processing world)
• continuous-time (analog)
• discrete-time (sampled analog signal or
  inherently discrete signal)
• continuous-value
• discrete-value
• random (noise)

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Synchronization (Timing the Communication)
CPU State Transition
EMS Figs 3.1 and 3.2 p. 143
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Synchronization (Timing the Communication)
EMS Figs 3.3 and 3.4 p. 144
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Latency

• Latency
• Real-Time Systems
• Throughput (Bandwidth)

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Synchronization Techniques(Im just waiting on a
friend)

• blind cycle open door at precisely 204 pm
• busy wait (gadfly) stand at the door
• interrupt keep busy until doorbell rings
• periodic polling doorbell broke, check every 5
  minutes
• DMA friend lets herself in

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Blind Cycle (Input)
char Input (void) PULSE Timer_Wait(5) retur
n(PORT)
Figs 3.5 and 3.6 from EMS
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Blind Cycle (Output)
void Output (unsigned char LETTER)
PORTLETTER Pulse() Timer_MsWait(100)
Figs 3.5 and 3.6 from EMS
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Busy Wait (Gadfly)
/ use spinlock to wait for i to change. /
static void f1() while (i0) / do
nothing - just keep checking over and over /
printf("i's value has changed to d.\n", i)
return NULL
Figs 3.7 from EMS
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Interrupt (IN)
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Interrupt (OUT)
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Periodic Polling
do / play games, read, / / poll to
see if ready / status areWeThereYet()
while (status NO)
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Motivations for Various Synchronization Techniques
EMS Table 4.1 p. 193
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Peripherals and I/O

• Ports
• Device Drivers and Interfaces
• Control and Status Registers
• Synchronization

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Peripherals and I/O

• I/O
• Ports
• Device Drivers and Interfaces
• Control and Status Registers
• Synchronization
• Signal Processing
• Signal Types
• Sampling
• A/D Conversion

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Input (Sensors) and Output (Actuators)

• Force
• Position
• Motion (Acceleration, Velocity)
• Temperature, Humidity
• Chemical
• Sound
• Shape / Texture / Color
• Motors (DC, Stepper, Servo)
• LCD Display
• LEDs
• Alarm
• Microwaves

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Signals

• Signal
• a time varying physical phenomenon which is
  intended to convey information.

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Relating to the outside world

• 4 categories of interfaces
• parallel (digital, simultaneous bits at a time)
• serial (digital, one bit at a time)
• analog (voltage, continuum)
• time (analog period, frequency, )
• Types of Signals (signal processing world)
• continuous-time (analog)
• discrete-time (sampled analog signal or
  inherently discrete signal)
• continuous-value
• discrete-value
• random (noise)

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Types of Signals
SS Fig. 1.3-1.5 p. 3
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Computer ScienceThe Art of Compromise (or The
Art of Abstraction)
Accuracy

Space
Time
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Sampling Methods

• Sample and Hold (S/H)

SS Fig 7.1 p. 493
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What computers understand
SS Fig 7.2 p. 493
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Analog to Digital Conversion (ADC)

• continuous-time, continuous-value
• ? discrete-value, continuous-time
• Using the process of
• Sampling
• Quantization
• Encoding

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ADC Process
SS Fig. 1.6 p. 4
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Sampling

• fs Sampling Frequency
• Ts Sampling Period (time between samples)

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Quantization

• if n is the word length of the ADC
• then
• quantization noise

SS Fig. 7.4 p. 494
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ADC Process
SS Fig. 1.6 p. 4
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Encode
SS Fig. 1.8 p. 5
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ADC Process
SS Fig. 1.6 p. 4
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Sinusoidal Signals
RED 20sin(2pi50t) BLUE 40sin(2pi50t)
RED 40sin(2pi25t) BLUE 40sin(2pi50t)
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Linear Combination of Sinusoids(Fourier Series)
SS Fig. 4.4 p. 211
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Sampling a Sinusoid(How often, is often enough?)

• Shannons Sampling Theorem
• If sampled at a rate more than twice the highest
  frequency (of the component sinusoids)
• it can be exactly reconstructed.
• fm Nyquist Frequency highest frequency
• 2fm Nyquist Rate

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Sampling a Sinusoid(How often, is often enough?)
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Sampling a Sinusoid(How often, is often enough?)
SS Figs 7.36, 7.37, 7.38
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Sampling a Sinusoid(How often, is often enough?)
SS Figs. 7.39, 7.41 p. 515
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Sampling a Sinusoid(How often, is often enough?)
RED 40sin(2pi25t) BLUE
40sin(2pi50t) BLACK BLUE RED
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Sampling a Sinusoid(How often, is often enough?)
RTS Fig. 1.2 p. 4
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Signal Processing (sub-basics)

• Signal Types
• Sampling
• A/D Conversion

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I/O and Peripherals
Key Concepts and Terms

• control and status registers
• ports
• bitmasking
• bit manipulation
• device drivers
• memory mapped I/O
• bandwidth
• synchronization
• polling
• busy waiting

• serial and parallel interfaces
• analog and digital signals
• analog to digital conversion
• sampling frequency
• active high, active low
• edge-triggered
• level triggered
• timing diagram