Processors

Introduction
Tabs
Manual Editing

Introduction

The MIPS processor and coprocessors are displayed on the right-hand side at all times, even when you are not running a program. While writing your program, this serves as a useful reference for register names and their conventional uses (hover mouse over the register name to see tool tips).

Tabs

Processor

The primary MIPS processor. Displayed here is the register file containing all general-purpose registers (GPRs) from $zero / $0 to $ra / $31, as well as the special HI / LO registers and the current value of PC (the Program Counter, which is the address of the next instruction to be fetched from memory).

Coprocessor 1

The MIPS floating-point coprocessor, also known as the float processing unit (FPU). Displayed here is the register file containing all floating-point registers (FPRs) from $f0 to $f31, as well as a checkbox for each of the eight FPU condition flags. (On a real MIPS FPU, these condition flags would instead be eight bits of the FCSR, or float control / status register, which also manages rounding modes and how floating-point exceptions are handled. MARS Red currently does not simulate the rest of this register, though.)

Coprocessor 0

The MIPS system control coprocessor, which normally handles most kernel-related operations such as memory management and exception / trap handling. Only a small subset of this functionality is simulated by MARS Red, so most of the registers in the register file are left blank and should not be accessed by any program. When a simulated program receives a MIPS exception / trap / interrupt, this tab will be selected, as the registers are updated with basic information about the event that occurred.

Manual Editing

Most of the registers listed in these tabs can be modified manually by double-clicking the desired cell in the Value column. Coprocessor 1 supports manual entry for both Single and Double, and interprets decimal values as their corresponding floating-point representations.