XSM Machine Organisation
Processor
The processor has two fundamental modes of operation - privileged and unprivileged
In Privileged, the program has access to the entire memory and disk In Unprivileged, the program has access to only the virtual machine instruction set
XSM Machine Registers
The XSM architecture maintains 29 registers, each capable of storing a word.
| Registers | Purpose | Access Mode |
|---|---|---|
| *R0-R19 | General Purpose User Registers R16-R19 are reserved for the use of SPL compiler |
Unprivileged |
| BP, SP, IP | Base, Stack and Instruction Pointers | Unprivileged |
| PTBR, PTLR | Page Table (Base, Length) Registers | Privileged |
| EIP, EC, EPN, EMA | Exception Status Registers | Privileged |
| P0-P3 (Ports) |
P0-Input port, P1-Output port P2,P3-Unused |
Privileged |
| Be cautious with R12-R15 |
Memory
Memory refers to the physical memory of the machine. The memory is organized as a sequence of pages. Each page is a sequence of 512 words. The total number of pages available is 128.
| Page Number | Contents | Word Address | Number of Words |
|---|---|---|---|
| 0 | ROM Code | 0 - 511 | 512 |
| 1 | Page for loading the BOOT block | 512 - 1023 | 512 |
| 2 - 3 | Exception handler (INT 0) | 1024 - 2047 | 1024 |
| 4 - 5 | Timer Interrupt (INT 1) | 2048 - 3071 | 1024 |
| 6 - 7 | Disk Interrupt (INT 2) | 3072 – 4095 | 1024 |
| 8 - 9 | Console Interrupt (INT 3) | 4096 – 5119 | 1024 |
| 10 - 11 | INT 4 (Create, Delete) | 5120 - 6143 | 1024 |
| 12 - 13 | INT 5 (Seek, Open, Close) | 6144 - 7167 | 1024 |
| 14 - 15 | INT 6 (Read) | 7168 - 8191 | 1024 |
| 16 - 17 | INT 7 (Write) | 8192 - 9215 | 1024 |
| 18 - 19 | INT 8 (Fork) | 9216 - 10239 | 1024 |
| 20 - 21 | INT 9 (Exec) | 10240 - 11263 | 1024 |
| 22 - 23 | INT 10 (Exit) | 11264 - 12287 | 1024 |
| 24 - 25 | INT 11 (Getpid, Getppid, Wait, Signal) | 12288 - 13311 | 1024 |
| 26 - 27 | INT 12 (Logout) | 13312 - 14335 | 1024 |
| 28 - 29 | INT 13 (Semget, Semrelease) | 14336 - 15359 | 1024 |
| 30 - 31 | INT 14 (SemLock, SemUnLock) | 15360 - 16383 | 1024 |
| 32 - 33 | INT 15 (Shutdown) | 16384 - 17407 | 1024 |
| 34 - 35 | INT 16 (Newusr, Remusr, Setpwd, Getuname, Getuid) | 17408 - 18431 | 1024 |
| 36 - 37 | INT 17 (Login) | 18432 - 19455 | 1024 |
| 38 - 39 | INT 18 (Test0, Test1, Test2, Test3) | 19456 - 20479 | 1024 |
| 40 - 127 | Unreserved Pages | 20480 - 65535 | 45056 |
| The last 19 words of page 0 are reserved for an interrupt vector table with 19 entries. Each entry points to the page number where the handler for the interrupt routine exists. |