datorteknik operatingsystem bild 1 the operating system (os)

Datorteknik OperatingSystem bild 1

the Operating System (OS)


The Operating System (OS)

Operating System

P1: Editor

P2: Compiler

P3: QuakeArena

MIPS

At any one time the processor (MIPS) is only excecuting one program (process).


Our Assembler

.data

.kdata

.text

.ktext

User

Kernel


The Hardware

.data

.kdata

.text

.ktext

User

Kernel

OKERROR!


How does the User program pass control to the Operating System?

Take control on ERROR Pass control explicitly


ERROR

Ex, Arithmetical Overflow

li $4 0x80000000

neg $4 $4

(sub $4 $0 $4)

0x00000000

- 0x80000000

0x80000000

Sign differs

Same Sign ! ERROR


Signed/Unsigned Arithmetics

The only difference is that– Unsigned never causes ERROR

– Signed causes ERROR on Overflow etc.

Signed

ADDSUBADDI..

Unsigned

ADDUSUBUADDIU..


Memory Error

Instruction Memory = Bad PC Data Alignment Error Access Protected Memory from User mode Nonexistent Memory (Page fault Chapter 7)


Do not confuse !

A Memory that tells the pipeline to Wait– relate to “cache miss”

A Memory Error or Page Fault– realte to “TLB miss”


The Consequence

A Memory that tells the pipeline to Wait

–Pipeline Stall A Memory Error or Page Fault

–Exception


Pass control excplicitly

The User wants some service from the Operating System– File I/O

– Graphics

– Sound

– Allocate Memory

– Terminate Program (no HALT instruction in real MIPS)

SYSCALL (casuses an exception)


How to choose service:

Is there different SYSCALLs? NO! Only one, use a register ($a0) to choose Use other registers ($a1,...) as parameters Use $v0 for result

ori $a1 $r0 ‘A’ ; Char ‘A’ori $a0 $r0 0x00 ; Write Charsyscallori $a0 $r0 0x01 ; Read Charsyscallor $a1 $r0 $v0 ; Move result $v0->$a1ori $a0 $r0 0x00 ; Echo Charsyscall


Other ways for the Operating System to take control?

External Interrupts, (not caused by User program)– Timers

– Harddisk

– Graphics

– Sound

– Keyboard, Mouse, other perhipals


Coprocessor CP0

8 Bad Memory Address 12 Status Register 13 Cause Register 14 Exception Address


Status Register CP0 ($12)

“Mode Stack” External Interrupt enable/disable


“Mode Stack”

OLD PREVIOUS CURRENT

KU IE

0 Kernel Mode1 User Mode

0 External Interrupt Disable1 External Interrupt Enable

KU

IE

KU IEKU IE5 0


Exception / Interrupt Occurs


KU IE KU IEKU IE

KU IEKU IE 0 0

0 Kernel Mode1 User Mode

0 External Interrupt Disable1 External Interrupt Enable

KU

IE


RFE Instruction (priviliged)


KU IE KU IEKU IE

KU IEKU IE? ?

We restore the PREVIOUS (KU,IE) into CURRENT


External Interrupts

Bit 0, (Current Interrupt Enable)– All External Interrupts Enable/ Disable

Bit 15..10, (individual interrupt enable)

INT 4 INT 3 INT 2 INT 1 INT 0 Current IE............

INT 5

15 10 0


Enable External Interrupt 2

Bit 0 = 1, (External Interrupt Enabled) Bit 12 = 1, Interrupt 2 Enabled

Current IE = 1............

15 10 0

INT 4 INT 3 INT 2 INT 1 INT 0INT 5

0 0 0 0 01


Cause Register (CP0 $13)

Bit 5..2, Exception Cause Code Bit 15..10, Interrupt Pending Bit 31, Exception Occur In Branch Slot

10

INT 5 INT 4 INT 3 INT 2 INT 1 Ex 3 Ex 2 Ex 1 Ex 0BS

5 231 15

INT 0.... .... ...

Exception Cause Codesee Table 4.3 LSI Logic

Pending Interrupts


Check if Interrupt 2 Pending

Mask with bit 12

15 10

INT 4 INT 3 INT 2 INT 1 INT 0INT 5

AND

0 0 0 0 0

CP0 $13

0 0 0 0 01

INT 2


Resume User Program

CP0 $14 Holds the Exception Address

(Addr to instruction in EX stage)

mfc0 $k0 $14 ; resume address

jr $k0 ; $k0 kernal reg

rfe ; “delayed branch”


Shared “Stack”

Assume that the User program uses the stack:

Can the Kernal use the same stack ($sp)?

Yes, but remember never to use memory below $sp, it will be destroyed (overwritten)!!

$sp

$sp User Data

User Data

User Data

User Data

Kernal Data

Kernal Data

datorteknik operatingsystem bild 1 the operating system (os)

Documents

error slide

current slide

os slide

perhipals slide

exception address slide

exception interrupt

ktext user kernel slide

page fault exception