1. 1 COMP541 Completing the MIPS Datapath Montek Singh Mar 27, 2007

2. 2 Datapath Lab  Last Friday’s lab: Included this  Need more: also memory/control

3. 3 Next few labs  March 30: lw and sw and branching  April 6: Complete CPU (Holiday?) Add VGA, keyboard/joystick Add VGA, keyboard/joystick

4. 4 Next Lab  Implement the lw and sw instructions.  The address for lw/sw generated by ALU Format Format sw $r1, 100($r2) sw $r1, 100($r2) Store contents of register 1 to Store contents of register 1 to address $r2 + 100 address $r2 + 100  Implement branch instructions

5. 5 Store Word  Easier  Just disable writing to register  Set an address and write to memory Could use second memory port and write on same cycle as next instruction Could use second memory port and write on same cycle as next instruction  Let’s look at block diagram…

6. 6 Block Diagram (just lw/sw)

7. 7 R-Type and lw/sw

8. 8 Load Word  Need to determine memory address Using ALU Using ALU  Then need to read memory and write to register

9. 9Careful  If you use one memory port, your instruction will disappear You could use the other memory port You could use the other memory port Could add an instruction register Could add an instruction register  More complex control  Harvard Architecture another possibility

10. 10 Sign Extension  Don’t get sidetracked into complexity  Just extend value of bit 15 to upper 16 bits  How?

11. 11Branching  Add beq (branch on equal)  That should give enough breadth to actually write full programs

12. 12 Resulting MIPS Datapath

13. 13 With Control

14. 14Memory  Addressing Byte address or word address? Byte address or word address?

15. 15 The MIPS Datapath

16. 16 Expanding Memory Block  First let’s look in detail at data memory block  See how to add block memories  Add I/O

17. 17 Memory Block Signals Address – 32 bits Write Data – 32 bits Read Data – 32 bits Mem Write – 1 bit Mem Read – 1 bit

18. 18 Using 2 Block RAMs  Illustration from book  Let’s work it out for Block RAMs  Specs next

19. 19 Block RAM Specs  Try 2 256x16

20. 20 Adding More Memory  Illustration from text  Could add 2 more block RAMs to increase mem to 512 words

21. 21 Memory Map  Refers to how physical memory is populated  In our example, memory from 0 to 511 It’s in two blocks, but that’s invisible to programmer It’s in two blocks, but that’s invisible to programmer

22. 22 Another Portion of Memory  Let’s see how to add a block of x8 character memory for the VGA  Need to make 24 bits be zero

23. 23 Memory Map Instruction and Data Memory Empty Character Memory 0 01 0000 0000 -256 10 0000 0000 512

24. 24 Adding I/O  Look at memory-mapped I/O  Conceptually like this

25. 25 In Reality  Isolated from CPU  On standard buses PCI PCI  Ours will be simpler Just memory addresses Just memory addresses

26. 26Later  You’ll add joystick or keyboard (or both) into memory locations that you can read

27. 27 How Does Processor Begin?  One way is to initialize PC to 0  Make sure to have instructions there Real computers have flash memory to boot CPU or go to configuration utility Real 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