75 lines
3.3 KiB
Text
75 lines
3.3 KiB
Text
# Internals: Nga Virtual Machine
|
|
|
|
## Overview
|
|
|
|
At the heart of RETRO is a simple MISC (minimal instruction
|
|
set computer) processor for a dual stack architecture.
|
|
|
|
This is a very simple and straightforward system. There are
|
|
30 instructions. The memory is a linear array of signed 32
|
|
bit values. And there are two stacks: one for data and one
|
|
for return addresses.
|
|
|
|
## Instrution Table
|
|
|
|
Column:
|
|
|
|
0 - opcode value
|
|
1 - Muri assembly name
|
|
2 - Full name
|
|
3 - Data Stack Usage
|
|
4 - Address Stack Usage
|
|
|
|
+--------------------------------------------------+
|
|
| 0 .. nop - - |
|
|
| 1 li lit -n - |
|
|
| 2 du dup n-nn - |
|
|
| 3 dr drop n- - |
|
|
| 4 sw swap xy-yx - |
|
|
| 5 pu push n- -n |
|
|
| 6 po pop -n n- |
|
|
| 7 ju jump a- - |
|
|
| 8 ca call a- -A |
|
|
| 9 cc conditional call af- -A |
|
|
| 10 re return - A- |
|
|
| 11 eq equality xy-f - |
|
|
| 12 ne inequality xy-f - |
|
|
| 13 lt less than xy-f - |
|
|
| 14 gt greater than xy-f - |
|
|
| 15 fe fetch a-n - |
|
|
| 16 st store na- - |
|
|
| 17 ad addition xy-n - |
|
|
| 18 su subtraction xy-n - |
|
|
| 19 mu multiplication xy-n - |
|
|
| 20 di divide & remainder xy-rq - |
|
|
| 21 an bitwise and xy-n - |
|
|
| 22 or bitwise or xy-n - |
|
|
| 23 xo bitwise xor xy-n - |
|
|
| 24 sh shift xy-n - |
|
|
| 25 zr zero return n-n | n- - |
|
|
| 26 en end - - |
|
|
| 27 ie i/o enumerate -n - |
|
|
| 28 iq i/o query n-xy - |
|
|
| 29 ii i/o invoke ...n- - |
|
|
| |
|
|
| Each `li` will push the value in the following |
|
|
| cell to the data stack. |
|
|
+--------------------------------------------------+
|
|
| li du mu .. |
|
|
| i lidumu.. 00000001:00000010:00010011:00000000 |
|
|
| data for li |
|
|
| d 2 00000000:00000000:00000000:00000010 |
|
|
| |
|
|
| Assembler Directives Instruction Bundles |
|
|
| ======================== ==================== |
|
|
| : label Combine instruction |
|
|
| i bundle names in groups of 4 |
|
|
| d numeric-data |
|
|
| r ref-to-address-by-name Use only .. after |
|
|
| s null-terminated string ju, ca, cc, re, zr |
|
|
+--------------------------------------------------+
|
|
|
|
## Misc
|
|
|
|
There are 810,000 possible combinations of instructions. Only
|
|
73 are used in the implementation of RETRO.
|