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updated documentation, a bit

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raphy 2023-06-12 16:23:30 +02:00
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spec.md
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@ -11,7 +11,7 @@ Since I'm studying riscV, this will be a lot riscv inspired.
The gravejit virtual machine sports 16 16-bit registers (plus the program counter!) and 16 operations.
Here is the list of registers togheter with memonics.
```
0 : zero // register 0 is always 0.
1 : ra // return address
2 : sp // stack pointer
@ -30,27 +30,28 @@ Here is the list of registers togheter with memonics.
15: t4 // don't know what to do with this
pc: program counter.
```
## ISA
opcode | memonic | format | description
0000 | NOP | just 0s'| Does nothing.
0001 | ADD s0 s1 s2 | R | s0 = s1 + s2
0010 | SUB s0 s1 s2 | R | s0 = s1 - s2
0011 | AND s0 s1 s2 | R | s0 = s1 && s2
0100 | XOR s0 s1 s2 | R | s0 = s1 xor s2
0101 | SLL s0 s1 s2 | R | s0 = s1 << s2
0110 | SLI s0 c | I | s0 = s0 << c
0111 | ADDI s0 c | I | s0 = s0 + c
1000 | BEQ s0 s1 s2 | R | if (s1 == s2) -> pc = s0
1001 | BGT s0 s1 s2 | R | if (s1 > s2) -> pc = s0
1010 | JAL s0 s1 c | J | s0 = pc+1; pc += s1 + c;
1011 |
1100 | LOAD s0 s1 s2 | R | loads s1 + shift by s2 in s0
1101 | STORE s0 s1 s2| R | stores s0 in address s1 + shift by s2
1110 | CALL s0 c | I | performs system call
1111 | HALT | just 1s'| halt, and possibly catch fire.
| opcode | memonic | format | description |
| ------ | -------------- | ------- | --------------------------------------- |
| 0000 | NOP | just 0s'| Does nothing. |
| 0001 | ADD s0 s1 s2 | R | s0 = s1 + s2 |
| 0010 | SUB s0 s1 s2 | R | s0 = s1 - s2 |
| 0011 | AND s0 s1 s2 | R | s0 = s1 && s2 |
| 0100 | XOR s0 s1 s2 | R | s0 = s1 xor s2 |
| 0101 | SLL s0 s1 s2 | R | s0 = s1 << s2 |
| 0110 | SLI s0 c | I | s0 = s0 << c |
| 0111 | ADDI s0 c | I | s0 = s0 + c |
| 1000 | BEQ s0 s1 s2 | R | if (s1 == s2) -> pc = s0 |
| 1001 | BGT s0 s1 s2 | R | if (s1 > s2) -> pc = s0 |
| 1010 | JAL s0 s1 c | J | s0 = pc+1; pc += s1 + c; |
| 1011 | | | #TODO? |
| 1100 | LOAD s0 s1 s2 | R | loads s1 + shift by s2 in s0 |
| 1101 | STORE s0 s1 s2 | R | stores s0 in address s1 + shift by s2 |
| 1110 | CALL s0 c | I | performs system call |
| 1111 | HALT | just 1s'| halt, and possibly catch fire. |
### Operation formats: