isa_overview

Overview of [as yet unnamed] ISA

Basics

• Multicycle processor
• 16 bit wordsize
• 16 operations
• 16 registers

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Instruction types

There are 5 types of instructions:

• Register instructions
• Set instructions
• Shift instructions
• Memory instructions
• Special instructions

Instruction format

Type	4 bits	4 bits	4 bits	4 bits
Register	Opcode	Destination register	Source register 1	Source Register 2
Set	Opcode	Target register	First half of value	Second half of value
Memory	Opcode	Destination register	Address register	Offset
Special	Opcode	Suboperation	Padding	Padding

Register instructions

Take values in 2 source registers, applies an operation as stated by opcode, stores in destination register

Set instructions

Take an 8 bit value and sets target register to that value

Memory instructions

Loads/stores a value into/out of target register from/to memory address equal to address register + offset bytes

Special instructions

Syscalls, io ops, and others. Arguments given as defined in relevant pages