Transcript Lecture 13
the Operating System (OS) Datorteknik OperatingSystem bild 1 The Operating System (OS) P1: Editor P2: Compiler P3: Quake Arena Operating System MIPS At any one time the processor (MIPS) is only excecuting one program (process). Datorteknik OperatingSystem bild 2 The Operating System (OS) P1: Editor P2: Compiler P3: Quake Arena Operating System MIPS At any one time the processor (MIPS) is only excecuting one program (process). Datorteknik OperatingSystem bild 3 The Operating System (OS) P1: Editor P2: Compiler P3: Quake Arena Operating System MIPS At any one time the processor (MIPS) is only excecuting one program (process). Datorteknik OperatingSystem bild 4 The Operating System (OS) P1: Editor P2: Compiler P3: Quake Arena Operating System MIPS At any one time the processor (MIPS) is only excecuting one program (process). Datorteknik OperatingSystem bild 5 The Operating System (OS) P1: Editor P2: Compiler P3: Quake Arena Operating System MIPS At any one time the processor (MIPS) is only excecuting one program (process). Datorteknik OperatingSystem bild 6 Our Assembler .text .data .ktext .kdata User Kernel Datorteknik OperatingSystem bild 7 The Hardware .text .data User ERROR! OK .ktext .kdata Kernel Datorteknik OperatingSystem bild 8 How does the User program pass control to the Operating System? Take control on ERROR Pass control explicitly Datorteknik OperatingSystem bild 9 ERROR Ex, Arithmetical Overflow li $4 0x80000000 neg $4 $4 (sub $4 $0 $4) 0x00000000 - 0x80000000 0x80000000 Sign differs Same Sign ! ERROR Datorteknik OperatingSystem bild 10 Signed/Unsigned Arithmetics The only difference is that – Unsigned never causes ERROR – Signed causes ERROR on Overflow etc. Signed Unsigned ADD SUB ADDI .. ADDU SUBU ADDIU .. Datorteknik OperatingSystem bild 11 Memory Error Instruction Memory = Bad PC Data Alignment Error Access Protected Memory from User mode Nonexistent Memory (Page fault Chapter 7) Datorteknik OperatingSystem bild 12 Do not confuse ! A Memory that tells the pipeline to Wait – relate to “cache miss” A Memory Error or Page Fault – relate to “TLB miss” Datorteknik OperatingSystem bild 13 The Consequence A Memory that tells the pipeline to Wait – Pipeline Stall A Memory Error or Page Fault – Exception Datorteknik OperatingSystem bild 14 Pass Control Explicitly The User wants some service from the Operating System – – – – – File I/O Graphics Sound Allocate Memory Terminate Program (no HALT instruction in real MIPS) SYSCALL (causes an exception) Datorteknik OperatingSystem bild 15 How to choose service: Is there different SYSCALLs? NO! Only one, use a register ($a0) to choose Use other registers ($a1,...) as parameters Use $v0 for result ori $a1 $r0 ‘A’ ori $a0 $r0 0x00 syscall ori $a0 $r0 0x01 syscall or $a1 $r0 $v0 ori $a0 $r0 0x00 syscall ; Char ‘A’ ; Write Char ; Read Char ; Move result $v0->$a1 ; Echo Char Datorteknik OperatingSystem bild 16 Other ways for the Operating System to take control? External Interrupts, (not caused by User program) – – – – – Timers Harddisk Graphics Sound Keyboard, Mouse, other perhipals Datorteknik OperatingSystem bild 17 Coprocessor CP0 8 Bad Memory Address 12 Status Register 13 Cause Register 14 Exception Address (EPC) Datorteknik OperatingSystem bild 18 Status Register CP0 ($12) “Mode Stack” External Interrupt enable/disable Datorteknik OperatingSystem bild 19 “Mode Stack” 5 OLD KU PREVIOUS IE KU IE CURRENT 0 KU IE KU 0 Kernel Mode 1 User Mode IE 0 External Interrupt Disable 1 External Interrupt Enable Datorteknik OperatingSystem bild 20 Exception / Interrupt Occurs OLD PREVIOUS CURRENT KU IE KU IE KU IE KU IE KU IE 0 0 KU 0 Kernel Mode 1 User Mode IE 0 External Interrupt Disable 1 External Interrupt Enable Datorteknik OperatingSystem bild 21 RFE Instruction (priviliged) OLD KU ? PREVIOUS IE ? CURRENT KU IE KU IE KU IE KU IE We restore the PREVIOUS (KU,IE) into CURRENT Datorteknik OperatingSystem bild 22 External Interrupts Bit 0, (Current Interrupt Enable) – All External Interrupts Enable/ Disable Bit 15..10, (individual interrupt enable) 15 INT 5 INT 4 INT 3 INT 2 INT 1 10 0 INT 0 Current IE ............ Datorteknik OperatingSystem bild 23 Enable External Interrupt 2 Bit 0 = 1, (External Interrupt Enabled) Bit 12 = 1, Interrupt 2 Enabled 15 10 INT 5 INT 4 0 0 INT 3 0 0 INT 2 INT 1 INT 0 1 0 0 ............ Current IE = 1 Datorteknik OperatingSystem bild 24 Cause Register (CP0 $13) 31 BS Bit 5..2, Exception Cause Code Bit 15..10, Interrupt Pending Bit 31, Exception Occur In Branch Slot 15 .... 10 INT 5 INT 4 INT 3 INT 2 INT 1 INT 0 Pending Interrupts 5 .... Ex 3 2 Ex 2 Ex 1 Ex 0 ... Exception Cause Code see LSI Logic User’s Manual Datorteknik OperatingSystem bild 25 Check if Interrupt 2 Pending Mask with bit 12 15 CP0 $13 AND 10 INT 5 INT 4 0 0 0 0 INT 3 INT 2 INT 1 INT 0 0 1 0 0 0 INT 2 0 0 Datorteknik OperatingSystem bild 26 Resume User Program CP0 $14 Holds the Exception Address (Addr to instruction in EX stage) mfc0 $k0 $14 jr $k0 rfe ; resume address ; $k0 kernel reg ; “delayed branch” Datorteknik OperatingSystem bild 27 Shared “Stack” Assume that the User program uses the stack: Can the Kernel use the same stack ($sp)? Yes, but remember never to use memory below $sp, it will be destroyed (overwritten)!! $sp Kernel Data Kernel Data $sp User Data User Data User Data User Data Datorteknik OperatingSystem bild 28