1 COMP541 Final Missing Pieces of MIPS: Adding Memory & I/O Montek Singh Apr 11, 2012

2 Summary of Remaining Labs, etc.  HW #2 (last one) assigned later today due Fri April 20 due Fri April 20  Lab Demos Fri April 20, 1-2:50pm Fri April 20, 1-2:50pm  grade by 4/23 Mon April 23, 1-3:30pm Mon April 23, 1-3:30pm  grade by 4/25 Wed April 25, 1-2:15pm: final chance for demos Wed April 25, 1-2:15pm: final chance for demos  grade by 4/27  Optional Take-Home Test #2 assigned April 20 assigned April 20 due anytime up until Apr 30, 3pm (final exam slot) due anytime up until Apr 30, 3pm (final exam slot)

Tasks for Lab Final Project/Demo  April 13: Lab 10 Completed Show: Show:  show a complete and working Lab 10 I will show you how to: I will show you how to:  add keyboard/joystick/mouse  integrate your VGA display code  April 13-20: Demo development Do: Do:  add any new instructions you need  develop your game/demo app (keep it simple!)  April 20, 23, 25: Show: Show:  show a complete and working final demo 3

A few tips on finishing up your MIPS  Sign extension: simple assume all of your I-type instructions are signed assume all of your I-type instructions are signed  e.g., lw, sw, addi, beq thus, simply sign-extend every immediate operand thus, simply sign-extend every immediate operand  just extend value of bit 15 to upper 16 bits  Add any other instrs needed slt could be very useful for loops! slt could be very useful for loops! you can do without all “unsigned” instructions you can do without all “unsigned” instructions  Do everything step-by-step! 4

This is your single-cycle MIPS 5

6Memories  Word width both instruction (IM) and data memories (DM) have 32-bit words both instruction (IM) and data memories (DM) have 32-bit words  be careful about word vs. byte addresses  i.e., whether or not to multiply/divide by 4 size IM so it can hold your code (say, 200 instructions) size IM so it can hold your code (say, 200 instructions) size DM so it can hold all your data (say, 100 words) size DM so it can hold all your data (say, 100 words) lw and sw should suffice lw and sw should suffice  skip lb and sb  they could be done in software

Memory-Mapped I/O  Simple technique for accessing I/O give each I/O device a “fake” memory address give each I/O device a “fake” memory address i.e., CPU reads and writes a specific range of memory locations for I/O devices i.e., CPU reads and writes a specific range of memory locations for I/O devices  using lw and sw  pretending I/O devices were simply memory locations  net effect is reading and writing I/O each device is assigned its own range of memory each device is assigned its own range of memory  “address space” example: example:  data memory from ’h0000_0000 to ’h0000_FFFF  VGA display (screen memory) from ’h1000_0000 to ’h1000_03FF  joystick status at ’h1100_0000  mouse status at ’h1100_0004  keyboard status at ’h1100_0008 … 7

8 Memory Map Data Memory Character Memory FFFF FF Do you test all bits in your memory decoder? Up to you.  Keep in mind: your character memory may have different word widths your character memory may have different word widths e.g., x1, or x8, etc. e.g., x1, or x8, etc. you may need to do some address and data conversion you may need to do some address and data conversion joystick, etc. gap

Memory Map  How to do in Verilog? Let’s do this interactively! Let’s do this interactively! 9

10 Adding I/O  Look at memory-mapped I/O  Conceptually like this

11 In Reality  Isolated from CPU  On standard buses PCI PCI  Ours will typically be simpler Just memory addresses Just memory addresses

12 Joystick, mouse, etc.  You’ll add joystick or keyboard (or both) into memory locations that you can read e.g., at two locations right above character memory e.g., at two locations right above character memory  I will show you on Fri

13 How Does Processor Begin?  One way is to initialize PC to 0 or some other predefined address or some other predefined address  Another possibility is to have a reset each time you hit a reset button, PC starts again at 0 each time you hit a reset button, PC starts again at 0  Make sure to have instructions there Modern computers have flash memory to boot CPU or go to configuration utility Modern computers have flash memory to boot CPU or go to configuration utility On (very) old computers had to enter boot program on front panel On (very) old computers had to enter boot program on front panel

Summary  Now we are done with creating a CPU!  Start creating your final demo! 14