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instructions.md

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List of Instructions

This file includes all real instructions of the RISC63 architecture. For each instruction, there is behavior and a potential assembly form provided. In the instructions definitions below, there are the following symbols used:

  • imm[n] – a sign extended immediate value, which fits into n bits
  • ra – a read and written register
    • also may be read-only or write-only
  • rb – a read register
  • cr – a control register
    • may be either read-only or write-only

If you would rather see instructions decoding, see decoding.md file.

Load and Store Instructions

  • ld ra, rb, imm[5]
  • st ra, rb, imm[5]

ld loads a 64-bit value from memory to ra. st stores a 64-bit value of ra to memory. In both cases, the memory address is computed as rb + 8 * imm.

Immediate Add Instructions

  • addi ra, imm[8]
  • addui ra, imm[8]
  • auipc ra, imm[8]
  • li ra, imm[8]

addi adds imm to ra. addui adds 256 * imm to ra. auipc adds 256 * imm to the instruction address and stores it to ra. li loads value imm to ra.

Conditional Jump Instructions

  • jz ra, imm[7]
  • jnz ra, imm[7]
  • aipc ra, imm[7]
  • jr ra, imm[7]

jz and jnz jump to the address in the range of 2 * imm relatively to the instruction address if the value of ra is equal and not equal to zero, respectively. aipc adds 2 * imm to the instruction address and stores it to ra. jr jumps to ra + 2 * imm address.

Immediate Arithmetic Instructions

  • slti ra, imm[6]
  • sltui ra, imm[6]
  • sgti ra, imm[6]
  • sgtui ra, imm[6]
  • srli ra, imm[6]
  • slli ra, imm[6]
  • srai ra, imm[6]
  • rsbi ra, imm[6]

slti and sgti store one to ra if ra is less than imm and ra is greater than imm, respectively. Otherwise, zero is stored. sltui and sgtui are similar except they perform unsigned comparisons. srli and slli perform a logical shift of ra by imm mod 64 bits to the right and left, respectively. srai performs an arithmetic shift to the right. rsbi stores imm - ra to ra.

Arithmetic and Logic Instructions

  • add ra, rb
  • sub ra, rb
  • and ra, rb
  • or ra, rb
  • xor ra, rb
  • slt ra, rb
  • sltu ra, rb
  • sgt ra, rb
  • sgtu ra, rb
  • srl ra, rb
  • sll ra, rb
  • sra ra, rb
  • rsb ra, rb

add adds rb to ra. sub subtracts rb from ra. and, or and xor perform appropriate logical operation over ra and rb and store the result into ra. The rest of the instructions behave similarly as in the section above except they use rb rather than imm.

Unconditional Jump Instruction

  • jmp imm[12]

jmp jumps to the relative address in the range of 2 * imm.

Data Manipulation Instructions

  • extb ra, rb
  • extw ra, rb
  • extd ra, rb
  • extbu ra, rb
  • extwu ra, rb
  • extdu ra, rb
  • insb ra, rb
  • insw ra, rb
  • insd ra, rb
  • mskb ra, rb
  • mskw ra, rb
  • mskd ra, rb

extb extracts a byte from ra, extends its sign bit and stores the result to ra. The three lowest bits of rb define the index of the affected byte. extbu does not extend the sign bit and uses zeros instead. insb inserts the lowest byte of ra to ra at the index defined by rb. The rest bits are cleared. mskb zeroes the byte of ra at the index. The rest instructions do similar operations for word (two bytes, two lowest bits) and double word (four bytes, lowest bit).

Control Register Instructions

  • crr ra, cr
  • crw ra, cr

crr reads cr to ra. crw writes ra to cr. The list of cr registers is available in the Control Registers section.

Move Instructions

  • mv ra, rb

mv copies rb to ra.

Instructions without Operands

  • nop
  • iret

nop does nothing. iret returns the processor from the interrupt.