RISC Programming
The RISC is a 32-bit interlocked integer processor with fixed-width, 32-bit instructions. An instruction can perform a scalar operation, two vector operations, a memory transfer, a branch, or a drawing operation. Integer operations are signed unless the instruction specifies otherwise. ALU overflow wraps; there are no instruction exceptions or status register.
Register file
| Operand index | Use |
|---|---|
%0..%31 | Hardwired constants. Writes are ignored. |
%32..%63 | Special hardware registers, additional constants and undefined indices. |
%64..%127 | Indirect aliases into %128..%255, selected through Seg. |
%128..%251 | General purpose registers. |
%252 / sp | Stack pointer. |
%253 / ira | Interrupt link register. |
%254 / ra | Program link register. |
%255 / fp | Frame pointer. |
The physical general purpose file contains 128 words. Indirect operand indices are aliases, not another 64 words. a0..a31 and q0..q15 are names for %128..%175 used by the drawing engines.
Special registers are never forwarded. Writes to writable special registers have the non-interlocked hazard specified for that register. %32..%46 may be used as a vector source, but not as a vector destination.
Instruction formats
The most significant byte is the opcode. The remaining bytes depend on the instruction:
| Format | Bits 31:24 | Bits 23:16 | Bits 15:8 | Bits 7:0 |
|---|---|---|---|---|
| Integer / draw / jmprl | OP | D | S2 | S1 |
| Store | OP | offset8 | S2 | S1 |
| Load | OP | D | offset8 | S1 |
| Sort | OP | S3 | S2 | S1 |
| li / lui | OP | D | immed16 | |
| sprii | OP | immed16 | S1 | |
| Branch | OP | offset16 | S1 | |
| Relative / absolute jump | OP | address24 | ||
For immediate ALU instructions, the S1 byte is an unsigned immediate. Vector operands must be double-word aligned. A v instruction uses two register pairs; vs uses the same scalar S1 value for both operations.
Opcode grid and instruction details · Integer operations · Loads and stores · Branches and jumps · Step instructions · Special registers
Sources: Technical Spec, p.5, Technical Spec, p.6, Technical Spec, p.7, Technical Spec, p.8