< Computer Architecture Lab < Winter2006 < PolzerJahn

SISP - Processor details & instruction set

Basic data

  • 16bit RISC CPU
  • 16 internal registers
  • von Neumann architecture
  • 16bit address bus
  • 32bit external data bus
  • two instruction widths (16 bit, 32bit)
  • External memory: 128 kB
  • Connection to a PC: standard serial interface (RS-232)
  • Number format: little endian
  • Signed arithmetic (two's complement)

Instruction set

Note: Instructions which take up 32 bit have an opcode higher than or equal to 0x20.

  • Basic operations:
Instruction Operation Opcode Description
NOP 0x00 No operation
MOV rA, rB rA <- rB 0x01 Copy the contents of one register to another.
  • Logical operations:
Instruction Operation Opcode Description
AND rA, rB rA <- rA AND rB 0x02 And conjunction of two registers
OR rA, rB rA <- rA OR rB 0x03 Or conjunction of two registers
NOT rA rA <- NOT rA 0x04 Logically inverts the contents of a register
XOR rA, rB rA <- rA XOR rB 0x05 Xor conjunction of two registers
  • Arithmetic operations:
Instruction Operation Opcode Description
ADD rA, rB rA <- rA + rB 0x06 Sum of two registers
ADC rA, rB rA <- rA + rB 0x13 Sum of two registers (uses carry)
SUB rA, rB rA <- rA - rB 0x07 Difference of two registers
SBB rA, rB rA <- rA + rB 0x14 Difference of two registers (uses carry)
INC rA rA <- rA + 1 0x08 Increments the contents of a register
DEC rA rA <- rA - 1 0x09 Decrements the contents of a register
NEG rA rA <- -rA 0x15 Negates the contents of a register
  • Shift operations:
Instruction Operation Opcode Description
SHL rA rA <- rA << 1 0x0A Shift left. Shifts the contents of a register to left by one bit, the right most bit is set to zero, the left most bit is stored in the carry flag
SHR rA rA <- rA >> 1 0x0B Shift right. Shifts the contents of a register to right by one bit, the left most bit is set to zero, the right most bit is stored in the carry flag
ASL rA rA <- rA << 1 0x16 Arithmetic shift left. Shifts the contents of a register to left by one bit, preserves sign, the left most bit is stored in the carry flag
ASR rA rA <- rA >> 1 0x17 Arithmetic shift right. Shifts the contents of a register to right by one bit, preserves sign, the right most bit is stored in the carry flag
ROL rA rA <- rA << 1 0x0C Rotate left through carry. Rotates the contents of a register to left by one bit, the right most bit is set to the value of carry, the left most bit is stored in the carry flag
ROR rA rA <- rA >> 1 0x0D Rotate right through carry. Rotates the contents of a register to right by one bit, the left most bit is set to the value of the carry, the right most bit is stored in the carry flag
  • Compare operations:
Instruction Operation Opcode Description
CMP rA, rB 0x0E Compares the contents of two registers
  • Input/output operations:
Instruction Operation Opcode Description
LDC rA, <IMM> rA <- IMM 0x20 Loads a constant value into a register
LD rA, rB rA <- MEM(rB) 0x0F Loads a value using indirect addressing from the memory to a register
ST rA, rB MEM(rB) <- rA 0x10 Stores the contents of a register into the memory using indirect addressing
INP rA, PORT rA <- PORT 0x11 Reads a value from an I/O Port
OUTP rA, PORT PORT <- rA 0x12 Writes a value to an I/O Port
LDIP rA rA <- IP + 1 0x19 Loads the address of the next instruction into the register.
  • Jump operations:
Instruction Opcode Description
JMP <ADDR> 0x21 Unconditional jump (target defined by second instruction word)
JMPR rA 0x18 Unconditional jump (target defined by the contents of rA)
JZ <ADDR> 0x22 Jump if zero. The instruction pointer is set to the defiend address, if the zero flag is set. Otherwise the execution continues with the next instruction.
JNZ <ADDR> 0x23 Jump if not zero. The instruction pointer is set to the defiend address, if the zero flag is not set. Otherwise the execution continues with the next instruction.
JL <ADDR> 0x24 Jump if lesser. The instruction pointer is set to the defiend address, if the lesser flag is set. Otherwise the execution continues with the next instruction.
JNL <ADDR> 0x25 Jump if not lesser. The instruction pointer is set to the defiend address, if the lesser flag is not set. Otherwise the execution continues with the next instruction.
JG <ADDR> 0x26 Jump if greater. The instruction pointer is set to the defiend address, if the greater flag is set. Otherwise the execution continues with the next instruction.
JNG <ADDR> 0x27 Jump if not greater. The instruction pointer is set to the defiend address, if the greater flag is not set. Otherwise the execution continues with the next instruction.

Flags

Name Changed by Default Description
Zero AND, OR, NOT, XOR, ADD, SUB, INC, DEC, CMP 0 If the result of an ALU operation is zero, this flag is set to 1. If the result is not zero the flag is set to 0.
Lesser CMP 0 This flag is set to 1 if the contents of the first register is lesser than the contents of the second one, otherwise it is set to 0.
Greater CMP 0 This flag is set to 1 if the contents of the first register is greater than the contents of the second one, otherwise it is set to 0.
Carry ADD, SUB, INC, DEC, SHL, SHR, ROL, ROR 0 This flag is set, if a operation creates an overflow or underflow.

Instruction format

  • Standard Instruction

8-bit Opcode, two 4-bit register numbers

Bits 0-7 8-11 12-15
Content OPCODE (REG1) (REG2 / PORT)
  • Extended instruction

8-bit Opcode, 4-bit register number (optional), 16 bit immediate value

Bits 0-7 8-11 12-15 16-31
Content OPCODE (REG) Reserved IMM

Pipeline

SIPS uses a four stage pipeline:

  • fetch
  • decode
  • execute
  • write back

This file contains a detailed graphical description of each stage.

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