Computer Organization Lecture 22

1. Computer OrganizationLecture 22 Project 6 Hard disk drive Bus arbitration University of Portland School of Engineering

2. Project 6 • Due: Friday, December 1 • Microprogram the instruction set • Complete MDP16 design • Execute a simple program • Extra credit for additional instructions University of Portland School of Engineering

3. MDP16 execution Program stores 0x25, 0x35, and 0x45 at 0x100, 0x101, 0x102 and reads the numbers back University of Portland School of Engineering

4. MicroROM contents University of Portland School of Engineering

5. Example trace $0 = 0x100 for address of sw University of Portland School of Engineering

6. Example trace, continued. Mem[100] = 0x25, Mem[101] = 0x35, Mem[102] = 0x45 University of Portland School of Engineering

7. Example trace, continued. Now load 0x100, 0x101, 0x102 into $1 University of Portland School of Engineering

8. Computer components • Input: receives information from external world • Output: transmits information to external world • Memory: holds programs and data • Data path: physical route that carries info • Control: coordinates overall flow of info University of Portland School of Engineering

9. System Bus The bus interconnects system agents University of Portland School of Engineering

10. ··· Agent 0 Agent n Signal 0 Signal 1 Bus ··· Signal n System view of a computer One Agent at-a-time owns the bus University of Portland School of Engineering

11. Agents • Goal: perform some function (memory, I/O, etc.) • Types • Master: can own the bus, assert signals • Slave: only responds when requested by master • Operations • Memory or I/O space • Read or write • Interrupt University of Portland School of Engineering

12. What type of agent? University of Portland School of Engineering

13. Moving-head disk Disk buses include EIDA, SATA, SCSI Performance = seek time + latency time + transfer time NOTE: Unique location denoted CHS  cylinder, head, sector University of Portland School of Engineering

14. Disk features • Platter: magnetically coated disk • Side: one of two platter surfaces • Arm: lever arm that swings across platter • Head: sensor that reads/writes data on platter • Track: circular region on platter • Cylinder: collection of tracks with same radius • Sector: region of a track, basic unit of data (B) University of Portland School of Engineering

15. Disk performance • Seek: time to move arm • Latency (rotational): time for platter to rotate to requested sector • Transfer: time to move data across bus University of Portland School of Engineering

16. High-end disk example Buffer = disk cache Host = PC disk controller University of Portland School of Engineering

17. Find disk bandwidth, transfer time? CLK = 100 ns, 32-bit data bus, 5 clocks/bus cycle, 512B sector University of Portland School of Engineering

18. Find the disk average latency? Twelve 5 cm platters, 7200 rpm, 120 GB University of Portland School of Engineering

19. ··· Agent 0 Agent n Signal 0 Signal 1 Bus ··· Signal n System view of a computer One Agent at-a-time owns the bus University of Portland School of Engineering

20. Example bus control signals? University of Portland School of Engineering

21. Bus cycle (phases) • Arbitration: owner defined • Address: ID of memory or I/O provided • Data: information transferred • Response: indicates completion of cycle Bus phases similar to instruction steps University of Portland School of Engineering

22. Bus timing Address Bus Driven Data Bus Driven Clk Breq Bgnt Ack ARB ADR DATA RESP University of Portland School of Engineering

23. Disk Mem-data Disk-Adr Mem Bus Cycle Bus timing example A little more complex Shared signals driven by different agents Disk Mem University of Portland School of Engineering

24. Bus arbitration • Serial: priority in-out, Request-Grant, sent from agent-to-agent (daisy-chain) • Parallel: each agent asserts unique request (centralized), one grant asserted • Distributed • Self-selection: agent codes combined to identify owner • Collision detection: request repeated after a delay University of Portland School of Engineering

25. Serial arbiter Each priority circuit ripples to next in line University of Portland School of Engineering

26. Design the priority circuit? Gnt = Pout = University of Portland School of Engineering

27. Device 1 Device 2 Device n ••• Req 1 Req 2 Req n Gnt 1 Gnt 2 Gnt n Central Arbiter Fixed, round-robin, multi-level, etc. Centralized arbitration More & fast logic, flexible algorithm University of Portland School of Engineering

28. Fixed centralize arbiter University of Portland School of Engineering

29. Simple RR arbiter Req3 11 Req2 Req1 10 01 Req0 00 Gntn = StatenReqn University of Portland School of Engineering

30. University of Portland School of Engineering

31. What type of agent? High-performance agents are often Masters University of Portland School of Engineering

32. Find disk bandwidth, transfer time? CLK = 100 ns, 32-bit data bus, 5 clocks/bus cycle, 512B sector University of Portland School of Engineering

33. Find the disk average latency? Twelve 5 cm platters, 7200 rpm, 120 GB University of Portland School of Engineering

34. Example bus control signals • Bus request, bus grant • Read, write • Memory space, I/O space • Address valid, data valid • Wait • Interrupt request, interrupt acknowledge University of Portland School of Engineering

35. Gnt = Req · Pin Pout = Req · Pin Design the priority circuit? University of Portland School of Engineering