Each LIT instruction holds an unsigned 7-bit immediate value to be concatenated to ToS. The first LIT sets the LIT_DIRTY flag, and subsequent ones cause ToS to be left-shifted by 7 before the new value is set.
Only unsigned values can be formed by concatenation, no sign-extension is done. For negative numbers, NEG instruction can be used.
The LIT_DIRTY flag is part of the flags saved and restored on the return stack.
These take as argument a frame index pointing to a register Rx. The frame index starts from the deepest stack element in the frame.
Frame accounting is implemented with register FSZ (frame size).
CALL instructions store a difference between the data stack depth and current FSZ value, so that FSZ can be restored by RET.
| Instruction | OP | Description |
|---|---|---|
| RPICK | 0 | Pushes Rx to stack |
| RSWAP | 1 | Swaps Rx and R0 |
| RMOV | 2 | Copies R0 to Rx and drops R0 |
| reserved | 3 |
| Instruction | OP | Description |
|---|---|---|
| DROP | 0 | |
| ADD | 1 | T = N + T |
| SUB | 2 | T = N - T |
| AND | 3 | Binary AND |
| OR | 4 | Binary OR |
| SHR | 5 | Right shift |
| SHL | 6 | Left shift |
| XOR | 7 | Binary XOR |
| reserved | ||
| MUL | 10 | Integer multiply |
| DIV | 11 | Integer divide |
| reserved |
| Instruction | OP | Description |
|---|---|---|
| DUP | 0 | Pushes T |
| NOP | 1 | No-op |
| NEG | 2 | Inverts T sign |
| INC | 3 | Increments T |
| DEC | 4 | Decrements T |
| NSWAP | 5 | Swaps next-on-stack with 3'rd on stack |
| FSZ | 6 | Pushes frame size |
| FSET | 7 | Sets frame size from T, consumming it |
| FKEEP | 8 | Keeps only topmost T in frame |
| RET | 9 | Return from function |
| CALL | 10 | Call frunction at T |
| JMP | 11 | Forward relative jump to PC + (T + 1) |
| LOOP | 12 | Backward relative jump to PC - (T + 1) |
| LJMP | 13 | Absolute jump to T addr |
| INT | 14 | Calls soft ISR |
| HALT | 15 | Suspend until interrupted |
These affect the TAKE_JUMP flag, initially set to true and reset by all jump instructions. Thus a jump without a preceding COND instruction is taken.
If the condition is true and TAKE_JUMP is true, TAKE_JUMP is preserved, else set to false.
The TAKE_JUMP flag is part of the flags saved and restored on the return stack.
| Instruction | OP | Description |
|---|---|---|
| CZERO | 0 | 0 == T |
| CNZERO | 1 | 0 != T |
| CEQ | 2 | N == T |
| CNEQ | 3 | N != T |
| CGEQ | 4 | N >= T |
| CLESS | 5 | N < T |
| reserved |