eXpOS Implementation

Introduction



This document discusses the mapping of various eXpOS data structures to the XSM machine's disk and memory. The implementation of eXpOS on XSM discussed in the project modularises the code of system calls into smaller module functions. An interface description of the module functions is given here. The document also outlines the useage of kernel stack of user processes.



Disk Organization


* The Disk layout of the XSM machine is as follows :

Block Number Contents Number of Blocks
0 - 1 Bootstrap 2
2 Disk Free List 1
3 - 4 Inode + User Table * 2
5 Root File ** 1
6 Reserved for future use 1
7 - 8 Init/Login Code 2
9 - 10 Shell Code 2
11 - 12 Idle Code 2
13 - 14 Library 2
15 - 16 Exception Handler 2
17 - 18 Timer Interrupt Routine 2
19 - 20 Disk Controller Interrupt Routine 2
21 - 22 Console Interrupt Routine 2
23 - 24 Interrupt 4 Routine: Create, Delete 2
25 - 26 Interrupt 5 Routine: Seek, Open, Close 2
27 - 28 Interrupt 6 Routine: Read 2
29 - 30 Interrupt 7 Routine: Write 2
31 - 32 Interrupt 8 Routine: Fork 2
33 - 34 Interrupt 9 Routine: Exec 2
35 - 36 Interrupt 10 Routine: Exit 2
37 - 38 Interrupt 11 Routine: Getpid, Getppid, Wait, Signal 2
39 - 40 Interrupt 12 Routine: Logout 2
41 - 42 Interrupt 13 Routine: Semget, Semrelease 2
43 - 44 Interrupt 14 Routine: SemLock, SemUnLock 2
45 - 46 Interrupt 15 Routine: Shutdown 2
47 - 48 Interrupt 16 Routine: Newusr, Remusr, Setpwd, Getuname, Getuid 2
49 - 50 Interrupt 17 Routine: Login 2
51 - 52 Interrupt 18 Routine: Test0, Test1, Test2, Test3 2
53 - 54 Module 0: Resource Manager 2
55 - 56 Module 1: Process Manager 2
57 - 58 Module 2: Memory Manager 2
59 - 60 Module 3: File Manager 2
61 - 62 Module 4: Device Manager 2
63 - 64 Module 5: Context Switch Module (Scheduler Module) 2
65 - 66 Module 6: Pager Module 2
67 - 68 Module 7: Boot Module 2
69 - 255 User Blocks 187
256 - 511 Swap Area 256
512 - 513 Secondary Bootstrap * 2
514 - 515 Interrupt 19 Routine: Test4, Test5, Test6, Test8 * 2
516 - 517 Module 8: Access Control Module * 2
518 - 519 Module 9: TestA (Unused) * 2
520 - 521 Module 10: TestB (Unused) * 2
522 - 523 Module 11: TestC (Unused) * 2
524 - 527 Unallocated * 4

* The Inode table occupies the first 960 words (60 entries each of size 16 words) in the disk blocks 3 and 4. User table occupies the next 32 words (16 entries each of size 2 words) and the last 32 words are reserved for future use.

** The Root File occupies the first 480 words of the 5th block and the last 32 words are unallocated.

* These disk blocks are available only on eXpOS running on NEXSM (a two-core extension of XSM) machine.

Memory Organization


* The Memory layout of the XSM machine is as follows :


Page Number Contents Word Address Number of Words
0 ROM Code 0 - 511 512
1 Page for loading the BOOT block (OS Startup Code) 512 - 1023 512
2 - 3 Exception Handler 1024 - 2047 1024
4 - 5 Timer Interrupt Routine 2048 - 3071 1024
6 - 7 Disk Controller Interrupt Routine 3072 - 4095 1024
8 - 9 Console Interrupt Routine 4096 - 5119 1024
10 - 11 Interrupt 4 Routine: Create, Delete 5120 - 6143 1024
12 - 13 Interrupt 5 Routine: Seek, Open, Close 6144 - 7167 1024
14 - 15 Interrupt 6 Routine: Read 7168 - 8191 1024
16 - 17 Interrupt 7 Routine: Write 8192 - 9215 1024
18 - 19 Interrupt 8 Routine: Fork 9216 - 10239 1024
20 - 21 Interrupt 9 Routine: Exec 10240 - 11263 1024
22 - 23 Interrupt 10 Routine: Exit 11264 - 12287 1024
24 - 25 Interrupt 11 Routine: Getpid, Getppid, Wait, Signal 12288 - 13311 1024
26 - 27 Interrupt 12 Routine: Logout 13312 - 14335 1024
28 - 29 Interrupt 13 Routine: Semget, Semrelease 14336 - 15359 1024
30 - 31 Interrupt 14 Routine: SemLock, SemUnLock 15360 - 16383 1024
32 - 33 Interrupt 15 Routine: Shutdown 16384 - 17407 1024
34 - 35 Interrupt 16 Routine: Newusr, Remusr, Setpwd, Getuname, Getuid 17408 - 18431 1024
36 - 37 Interrupt 17 Routine: Login 18432 - 19455 1024
38 - 39 Interrupt 18 Routine: Test0, Test1, Test2, Test3 19456 - 20479 1024
40 - 41 Module 0: Resource Manager 20480 - 21503 1024
42 - 43 Module 1: Process Manager 21504 - 22527 1024
44 - 45 Module 2: Memory Manager 22528 - 23551 1024
46 - 47 Module 3: File Manager 23552 - 24575 1024
48 - 49 Module 4: Device Manager 24576 - 25599 1024
50 - 51 Module 5: Context Switch Module (Scheduler Module) 25600 - 26623 1024
52 - 53 Module 6: Pager Module 26624 - 27647 1024
54 - 55 Module 7: Boot Module 27648 - 28671 1024
56 Process Table 28672 - 28927 256
Open File Table 28928 - 29055 128
Semaphore Table 29056 - 29183 128
57 Memory Free List 29184 - 29311 128
File Status Table 29312 - 29551 240
Disk Status Table 29552 - 29559 8
System Status Table 29560 - 29567 8
Terminal Status Table 29568 - 29575 8
Access Lock Table * 29576 - 29583 8
Unallocated 29584 - 29695 112
58 Page tables 29696 - 30015 320
Buffer Table 30016 - 30031 16
Disk Map Table 30032 - 30191 160
Unallocated 30192 - 30207 16
59 - 60 Memory copy of Inode Table 30208 - 31167 960
Memory copy of User Table 31168 - 31199 32
Unallocated 31200 - 31231 32
61 Memory copy of Disk Free List 31232 - 31743 512
62 Memory copy of Root File 31744 - 32223 480
Unallocated 32224 - 32255 32
63 - 64 Expos Library 32256 - 33279 1024
65 - 66 INIT/Login Program 33280 - 34303 1024
67 - 68 Shell Program 34304 - 35327 1024
69 - 70 Idle Program 35328 - 36351 1024
71 - 74 Buffer (disk cache) 36352 - 38399 2048
75 Reserved for future use (Exam!) 38400 - 38911 512
76 - 127 User Programs 38912 - 65535 26624
128 - 129 Page for loading the Secondary BOOT Block * 65536 - 66559 1024
130 - 131 Interrupt 19 Routine: Test4, Test5, Test6, Test7 * 66560 - 67583 1024
132 - 133 Module 8: Access Control Module * 67584 - 68607 1024
134 - 135 Module 9: TestA (Unused) * 68608 - 69631 1024
136 - 137 Module 10: TestB (Unused) * 69632 - 70655 1024
138 - 139 Module 11: TestC (Unused) * 70656 - 71679 1024
140 - 143 Reserved for future use * 71680 - 73727 2048

* These memory pages are available only on eXpOS running on NEXSM (a two-core extension of XSM) machine.
Note: Constants can be found here.

Kernel Module Interface

Kernel Stack Management

eXpOS Process Management Implementation

eXpOS File system and Implementation

eXpOS Multi-user Implementation