RTOS and Microcontroller

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RTOS and Microcontroller
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What is a Real Time System?

• Real-time systems process events
• External input events trigger other events to
  occur as outputs
• Minimizing response time is critical, or
  otherwise the entire system may fail to operate
  properly

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Real-Time Systems

• Most embedded systems are real-time
• Has timing constraints
• Make certain calculations or decisions in a
  timely manner
• A missed deadline is as bad as a wrong answer
• Consequences of a missed deadline
• - severe -gt hard real-time
• - acceptable -gt soft real-time

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Hard/Soft Real-Time Systems

• Soft Real-Time System
• - Computer output response as fast as possible,
  but
• no specific deadlines that must be met
• Hard Real-Time System
• - Output response must be computed by specified
  deadline or system fails

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Multi-Tasking and Concurrency

• Most real-time systems are also embedded systems
  w/several inputs and outputs and multiple events
  occurring independently
• Separating tasks simplifies programming, but
  requires somehow switching back and forth among
  the tasks (multi-tasking).
• Concurrency is the appearance of simultaneous
  execution of multiple tasks

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Basic Microprocessor

• A typical microprocessor has at least a
  collection of address pins, a collection of data
  pins, one or more of clock pins, a read pin, and
  a write pin

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Types of Memory(No-Volatile)

• ROM (Read Only Memory)
• - ROM stores programs
• - It is programmed at the semiconductor
  factory
• - Inexpensive permanent memory, best choice
  for
• a product with large volumes of program
• - Slower than RAM, cannot rewrite.

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• PROM (Programmable ROM)
• - PROM stores programs
• - It is shipped in blank, use a PROM
  programmer
• to program it
• - Used for lower volumes, but is more
  expensive
• than ROM
• - Can rewrite only once

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• EPROM (Erasable PROM)
• - Shipped in blank and is programmed with a
  PROM programmer
• - It can be erased by shining a strong
  ultraviolet light on it for 10 or 20 minutes and
  then reused
• - It is therefore useful when you are debugging
  a program.
• - Can rewrite many times

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• Flash
• - Flash(special EPROM with large volume).
• - Cannot change data very often due to slow
  writing

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Types of Memory(Volatile)

• RAM (Random Access Memory)
• - RAM is useful for data.
• - It is sometimes useful to load the program
  from ROM to RAM at power-up time
• - Very fast
• - No limit on write
• - The microprocessor can read the data from
  the RAM quickly, faster even than from ROM
• - The microprocessor can write new data to the
  RAM quickly, erasing the old data in the RAM as
  it does so
• - The RAM forgets its data if the power is
  turned off

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Types of RAM

• Static RAM
• - Static RAM remembers its data without any
  assistance
• from other parts of the circuit.
• - Static RAM parts look much like ROM parts,
  except that
• they have a write enable signal in
  addition to the other
• signals, which tells the RAM when it
  should store new
• data.

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Types of RAM

• Dynamic RAM
• - Dynamic RAM depends on being read once in a
  while,
• otherwise it forgets its data
• - Uses a circuit, often built into the
  microprocessor, called
• dynamic RAM refresh, whose sole purpose is
  to read data
• from the dynamic RAM periodically to make
  sure that the
• data stays valid.
• - Is cheap

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Microprocessor System (Microcontroller)

• The collection of data, address, and control
  signals that control the operation pace of the
  microprocessor, the ROM, the RAM is called the bus

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Memory Mapping and the I/O Address for I/O device

• Memory mapping and the I/O address for I/O device

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Direct Memory Access (DMA)

• Direct memory access (DMA) circuits move data
  directly from I/O devices to memory and vice
  versa without microprocessor intervention

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Interrupt

• Interrupts start with a signal form the
  hardware. Most I/O chips, that drive serial
  ports, parallel ports, or network interfaces,
  need attention when certain events occur.
• For example, when a serial port chip
  receives a character from the serial port, it
  needs the microprocessor to read that character
  from registers of the serial port chip itself and
  to store it in memory. Similarly, when a serial
  port chip sends one character, it need the
  microprocessor to send it the next character to
  be transmitted.

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Interrupt Connections
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Interrupt Hardware
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Universal Asynchronous Receiver/Transmitter and
RS-232

• A universal Asynchronous Receiver/Transmitter
  or UART is a common device on many systems. Its
  purpose is to convert data to and from a serial
  interface, that is, an interface on which the
  bits that make up the data are sent one from
  another. A very common standard for serial
  interfaces is the RS-232 interface, used between
  computers and modems and nowadays often between
  computers and mice.
• It converts data between an eight-bit format
  and the one-bit-at-a-time format used on serial
  ports such as RS-232 ports. UARTs are controlled
  by the microprocessor through a collection of
  registers (modem, mouse).

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