COP 4600

Objective # 3

So far………..

Obj#1 : read “logon.dat” and created our event list.

Obj#2 : function Boot() called. “boot.dat” was read. Kernel loaded and MEMMAP initialized.

Objective # 3

Interrupt_Handler() Logon_Service()

Creates a PCB Read “Script.dat”

Allocate memory And Load Program from

user’s script ……………………

Logon_Service()

Get_Script() Next_pgm()

Dealloc_pgm Get_Memory Loader

Dealloc_seg

Merge_seg

Get_InstrAllocate_segCompact_mem

I

II

III

IV

V

LEVEL - ILogon_Service() :

[ Allocates and Initializes the PCB for LOGON events ]

• PCB stored in termtable (array of pointers to PCB’s)

• termtable[...] = pcb;

• Initialize PCB .

• status, terminal, wait, request blocks, user

• Call Get_Script (PCB) // LEVEL II

{ Initialize the process script and pgmid }

• Call Next_pgm (PCB) // LEVEL II

{ Allocate and Load the next program from script }

LEVEL - IIGet_Script() :

[ Reads a script from “script.dat” ]

Open “script.dat”

Intialize pcb->script and pgmid

Read script till LOGOFF encountered.

Load script to PCB -> script[……] Compare script names against program names in the

program id table (pgmidtab) and assign corresponding int value to pcb->script[...]

This gives us the list of programs a user will execute.

LEVEL - IINext_pgm() :[ Makes a transition to the next program in the script if

possible]

If the next program is not the first program, remove previous

program from memory. if (pcb->pgmid >= 0 && pcb->rb == NULL)

Dealloc_pgm();

If a process has an unserviced I/O request block (rb),return without loading next program.

if (pcb->rb != NULL) return

If last program encountered, set PCB status to terminated. if (pcb->[pcb->pgmid] == LOGOFF)

print to *.out & set pcb->status = terminated. return

LEVEL – IINext_pgm() :[ Makes a transition to the next program in the script if

possible]

• Allocate and initialize, if possible, new segments table for the PCB program.

Get_memory(pcb);

• Load next program in memory. Loader(pcb);

• Initialize PCB area for saving CPU info (cpu_save) pcb cpu_save

Set PCB status to readypcb->status = ready;

LEVEL - IIIGet_Memory() :[ Allocates Segment Table and sets up information for

each segment ]Extract # of segments from first line of file & use it to allocate memory for the PCB segment table.

PROG_FILE [pcbscript[pcbpgmid]];Extract # of segments from first line of file & use it to allocate memory for the PCB segment table.

Read size of each segment + access bits in file. Store them in the PCB segment table. Also, compute the total memory required by these segments using the segment sizes.

mem_req += seg size

Check if memory required exceeds free memory. If so, exit.

LEVEL - IIIGet_Memory() :[ Allocates Segment Table and sets up information for

each segment ]

If memory available, call Alloc_seg() function for each segment with the length of the segment. X = Alloc_seg(pcb->segtable[…].len)

If memory allocated successfully, save memory base pointer pcb->segtable[…].membase = x;

Else call memory compactness function before calling memory allocation function Compact_mem();

x = Alloc_seg(pcb->segtable[i].len);

LEVEL - IVAlloc_seg() :

[ Searches the Free memory list for free memory segments in MEM for a segment with a length equal to that requested ]

Search list of free memory segments with the required size If length matches exactly, remove segment from free memory and return with base address of this segment. if (ptr->segment_size == len)

free_mem = ptr->next; return ptr->segptr;

If segment length more than required, move free memory pointer ahead by amount of length and return base pointer

of memory segment. ptr->segsize -= len; ptr->segptr += len;

Else, keep searching until one of the above conditions is met.

Return -1 if segment not found.

Decrement free memory by the size of the segment.

LEVEL - IIILoader() :

[Reads associated file for instruction and loads each

instruction into MEM]

For each segment, it reads each instruction in that

segment.

Calls Get_Instr() {OBJ #2} to get opcodes and

operands.

Get_Instr(pcb->script[pcb->pgmid], &instr);

Load each instruction in MEM

MEM[...].opcode = instr.opcode;

MEM[...].operand = instr.operand;

Call Display_pgm() {OBJ #2} to echo to *.out

LEVEL - III

Dealloc_pgm() :

[ Frees all allocated segments for the current program and then frees the segment table]

Call Dealloc_seg() for each segment in the pcbsegtable;

free(pcbsegtable);

pcb->segtable = NULL;

LEVEL - IV

Dealloc_seg() :

[ Return a segment to the free list]

Initialize segment ptr, its base and length. If free memory is NULL, this segment becomes free memory.

free_mem = ptr->seg;

If (pt_seg->segptr < free_mem->segptr) pt_seg->next = pt (pointer to free_mem);

free_mem = pt_seg;

Else if, find place in list where above condition is true and insert the memory segment.

Else, insert segment at end of list.

Increment free memory counter and call Merge_seg()

LEVEL - V

Merge_seg() :

[ Scans Memory list and if it finds two adjacent memory blocks it merges them into one ]

if (ptr->segptr + pt->segsize == ptr->next->segptr)

merge the two chunks

Abend_Service() :

[ Services SEGFAULT and ADRFAULT events]

• Print message to *.out that process Uxxx (given by termtable[...]->user) has terminated due to

segmentation fault or an address fault.• Call End_Service();

End_Service() :

[ Services PGMEND events]

Set PCB status to end and set active pcb to NULL pcb->status = end;

CPU.active_pcb = NULL;

If request block list is NULL, call Next_pgm(pcb) to advance the process script and prepare the next program for execution, if there is one if (pcb->rb == NULL)

Next_pgm(pcb);