embedded systems

1. GUIDED BY: PREPARED BY:
Prof. R.G.PATEL Vijay Yadav (140403111014)
Ravi chaudhri(140403111016)
Sankalchand Patel collage of engineering
Subject: Embedded Systems Subject code:2171005
Device Drivers and interrupt service mechanism

2. Content
Interrupt.
ISR concept.
 interrupt source.
 interrupt servicing (handling )mechanism.
 multiple interrupt.

3. Interrupt

4. Interrupt
 An interrupt is a signal (an “interrupt request”) generated by some event
external to the CPU
Causes CPU to stop currently executing code and jump to separate piece of
code to deal with the event
Sometimes things will happen in a system when the processor is simply not
ready. In fact, sometimes things change that require immediate attention.
Can you imagine, sitting at your PC, that you were to hit buttons on the
keyboard, and nothing happens on your computer?
 Maybe the processor was busy, and it just didnt check to see if you were hitting any
buttons at that time

5. Types Of Interrupts
 There are two types of interrupts.
 Hardware
 Software
 Software interrupts :
 are called from software, using a specified command.
 Hardware interrupts:
are triggered by peripheral devices outside the microcontroller.
 your embedded system may contain a timer that sends a pulse to the controller
every second.
 Your microcontroller would wait until this pulse is received, and when the pulse
comes, an interrupt would be triggered that would handle the signal.

6.  Interrupt handling code often called an ISR (“Interrupt Service Routine”)
When ISR is finished, execution returns to code running prior to interrupt.
 Interrupt Service Routines (ISR) are the portions of the program code that
handle the interrupt requests.
 When an Interrupt is triggered (either a hardware or software interrupt), the
processor breaks away from the current task, moves the instruction pointer
to the ISR, and then continues operation.
 When the ISR has completed, the processor returns execution to the
previous location.
Interrupt Service Routine:

7. Many embedded systems are called interrupt driven systems, because most of
the processing occurs in ISRs, and the embedded system spends most of its time
in a low-power mode.
ISR into two parts:
 top-half (fast interrupt handler, First-Level Interrupt Handler
(FLIH))
bottom-half (slow interrupt handler, Second-Level Interrupt
Handlers (SLIH)).
Top-half is a faster part of ISR which should quickly store minimal information
about interrupt and schedule slower bottom-half at a later time

9. Interrupt Sources
 Hardware Interrupts
▫Commonly used to interact with external devices or peripherals
▫Microcontroller may have peripherals on chip
 Software Interrupts
▫Triggered by software commands, usually for special operating system tasks]
• i.e. switching between user and kernel space, handling exceptions
 Common hardware interrupt sources
▫Input pin change
▫Hardware timer overflow or compare-match
▫Peripherals for serial communication
 UART, SPI, I2C – Rx data ready, tx ready, tx complete.
Watchdog timer timeout.
 ADC conversion complete.

10. Multiple interrupt
 Multiple interrupt-calls
 Interrupt-service calls
 There can be interrupt-service calls in case a number of higher
priority interrupt sources activates in succession.
• A return from any of the ISR is to the lower priority pending ISR
 Processor interrupt service mechanisms.
 Certain processors permit in-between routine diversion to higher
priority interrupts unless all interrupts or interrupts of priority
greater than the presently running routine are masked or ISR
executed DI instruction
 These processors provide in order to prevent diversion in between
the running ISR completely by provisioning for masking all
interrupts by primary level bit and or Instruction

12.  Hardware Assignment of priorities.
ARM7 provides two types of the interrupt sources (requests) ─ IRQs
(interrupt requests) and FIQs (fast interrupt requests).
Interrupts in 80x86 assigned interrupt-types and interrupt of type 0 has
highest priority and 255 as lowest priority
 Multiple sources of interrupts
 Multiple devices
 Processor hardware assigns a priority phw to each source (including traps
or exceptions) or sourcegroupa pre-assumed priority (or level or type).
 phw represents the hardware presumed priority for the source (or
group)Assume number be among 0, 1, 2, ..., k, ..., m-1.

13. Reference
www.google.com
www.wikipedia.com
Reface book
second edition raj kamal

14. THANK YOU