1 / 15

THE SYSTEM OF INTERRUPTS Definitions Questions (??) Classification of interrupts

THE SYSTEM OF INTERRUPTS Definitions Questions (??) Classification of interrupts The Interrupt Vector Table (IVT) The steps to execute a ISR The interrupt controller 8259 The sequence for “Interrupt Acknowledge” Applications of software interrupts. 1) Definitions.

lam
Download Presentation

THE SYSTEM OF INTERRUPTS Definitions Questions (??) Classification of interrupts

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. THE SYSTEM OF INTERRUPTS • Definitions • Questions (??) • Classification of interrupts • The Interrupt Vector Table (IVT) • The steps to execute a ISR • The interrupt controller 8259 • The sequence for “Interrupt Acknowledge” • Applications of software interrupts

  2. 1) Definitions • Need of communication between the uP and the peripheral devices • Idea: to interrupt the execution of the current program • Def: Interrupts + Interrupt Service Routine uP Peripheral devices

  3. 2) Questions • Who can interrupt the uP? (possibilities) • Hardware • Software  Classification of interrupts 2) What happens when an interrupt is accepted? 3) How the processor finds the address of ISR? 4) Then, which is the difference between a PROC and ISR? • Address (ISR), address (PROC) • End: ISR (iret), PROC (ret)

  4. 3) Classification of interrupts • Internal interrupts / exceptions • Hardware interrupts (from peripheral devices  data transfer; signals are used) • INTR – maskable interrupts • I=1 (STI) • I=0 (CLI) • NMI – non-maskable interrupts • NMI • When accepted? - At the end of an instruction cycle ! • How are the peripheral devices recognised? By a type number which is used by the processor as a pointer in the IVT to obtain the address of the ISR

  5. Classification (cont) c) Software interrupts INT k; k=0...255 (type of interrupt) Examples: INT 10h (video services) INT 14h (communication on serial interface)

  6. 4) The Interrupt Vector Table (IVT) • Implements a mechanism that associates for a specific interrupt request a service (handler or ISR). It stores the addresses of ISRs • 256 types of interrupt requests • What we need to obtain an address for ISR • CS & IP • Many ISRs : k=0 ... 255 (type of interrupts) • The structure of IVT • Location • Structuring (IP, CS), 256 entries • The input in the table is the “key k” (interrupt type) • Who delivers the key to the uP? (example of values)

  7. 5) The steps to execute a ISR • Peripheral device  interrupt controller (it associate a key K to the device); K-progr • I=1?- uP accepts the interrupt  INTA and asks for the key. The key is transmited to the uP. • The uP uses the key K to find out the address of the ISR (associates an ISR to the peripheral devices) • uP execute the ISR and then returns to the main program

  8. 6) The interrupt controller 8259

  9. Inputs on 8259 Explain: IRQi signals + connection of 2 controllers 8259 in the system

  10. 7) The sequence for “Interrupt Acknowledge” = a hardware mechanism to send the “key K” from the interrupt controller 8259 to the uP • The diagram of signals (if INTR and I=1) • Save on the stack: PSW, CS, IP, I=0, T=0 • It follows the sequence of INTA • 2 machine cycles • ALE • LOCK • INTA (1st activation, 2nd activation)  Key K 3) Point into IVT at address k*4 to get the address of ISR 4) Jump to ISR and execute it 5) IRET – returns in the main program

  11. 8) Applications of software interrupts VIDEO SERVICES (INT 10h) – BIOS level AH =2 (setting the cursor to a specific location) In: DH = raw, DL=column Exercise: position in the centre of the screen AH=3 (get current cursor position) Returns in DH=raw, DL=column, CX=the shape of the cursor Exercise: Move Relative Nx, Ny AH=6 (scroll up) In: AL=no of lines for scroll (AL=0, CLS), BH=attribute of blank raws CH=upper raw, CL=left column, DH=lower raw, DL=right column Example: Clear Screen AH= 9 (display a character from AL) AL, BH=video page, BL=atrribute, CX-rep Example: Display a string defined in DS, starting in raw 3 column 5 AH=0Eh (display char with increment of cursor)

  12. 8) Applications of software interrupts KEYBOARD SERVICES (INT 16h) – BIOS level AH =1 (test if keypressed) Return Z=0 if Keypressed, Z=1 if not Keypressed AH=0 (read the character) Returns in AH the scane code and in AL the ASCII code of the Key. Exercise: Read a string and display it, until ESC is pressed

  13. DOS services (INT 21h)

  14. INT 21h (cont) Documentation: INT 1Ah, INT 14h, INT 17h, INT 13h

More Related