System and method for point-to-point serial communication between a system interface device and a bus interface device in a computer system

• US 6,363,439 B1
• Filed: 12/07/1998
• Issued: 03/26/2002
• Est. Priority Date: 12/07/1998
• Status: Expired due to Term

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: Lester, Robert Allan, Ferguson, Patrick L., Battles, John D., Rawlins, Paul B.
• Primary Examiner(s): Lee, Thomas
• Assistant Examiner(s): Perveen, Rehana
• Application Number:
  US09/206,515
• Time in Patent Office: 1,205 Days
• Field of Search: 710/110, 710/106, 710/107, 710/117, 710/36, 710/45
• US Class Current: 710/36
• CPC Class Codes: G06F 13/4004 Coupling between buses
• CPC Class Codes: G06F 13/4273 using a clocked protocol

Abstract

A point-to-point serial communication link between a system interface unit and a peripheral bus interface unit is provide. The system bus interface unit may interface between a CPU bus and a peripheral bus, such as the PCI bus, and may be referred to as a north bridge. The system interface unit may also interface to main memory and to an advanced graphics port. The peripheral bus interface unit may interface between a first peripheral bus, such as the PCI bus, and a second peripheral bus, such as an ISA bus, and may be referred to as a south bridge. The serial communication link between the system interface unit and the bus interface unit may be a one wire serial bus that uses a bus clock from the first peripheral bus as a timing reference. This clock may be the PCI clock. The serial communication link may use a single pin on the system interface unit and a single pin on the bus interface unit to transfer commands between the interface units. A pull-up device may be provided on the serial communication link to maintain a high voltage level on the link when it is not being driven by one of the bus interface units. The north bridge and south bridge may alternate between sending and receiving commands across the

Claims

1. A computer system, comprising:

a system interface unit configured to interface a processor bus to a first peripheral bus;

a bus interface unit configured to interface said first peripheral bus to a second peripheral bus;

a serial communication link between said system interface unit and said bus interface unit;

said system interface unit and said bus interface unit are further configured to communicate with each other across said serial communication link;

a graphics device coupled to said system interface unit; and

a display monitor for displaying images to a user of the computer system, wherein

said display monitor is coupled to said graphics device.

2. The computer system as recited in claim 1, wherein said system interface unit and said bus interface unit are configured to communicate with each other across said serial communication link by sending commands across said serial communication link, wherein said system interface unit and bus interface unit are configured to alternate after each command between which device is sending and which device is receiving a command.

3. The computer system as recited in claim 1, wherein said system interface unit and said bus interface unit are configured to synchronize sending and receiving commands across said serial communication link to a common clock reference.

4. The computer system as recited in claim 3, wherein said common clock reference is a bus clock for said first peripheral bus.

5. The computer system as recited in claim 4, wherein said first peripheral bus comprises a Peripheral Component Interconnect (PCI) bus.

6. The computer system as recited in claim 1, wherein said system interface unit and said bus interface unit are configured to communicate with each other across said serial communication link by sending commands across said serial communication link, wherein said system interface unit and bus interface unit are configured to alternate after each command between which device is sending and which device is receiving a command, wherein neither said system interface unit nor said bus interface unit drives said serial communication link for a turnaround period after a command is sent.

7. The computer system as recited in claim 6, further comprising a pull-up device on said serial communication link to pull said serial communication link to a high voltage when said serial communication link is not actively driven.

8. The computer system as recited in claim 1, wherein said serial communication link is a single connection between one conductor on said system interface unit and one conductor on said bus interface unit.

9. The computer system as recited in claim 1, wherein said system interface unit and said bus interface unit are configured to communicate system information across said serial communication link.

10. The computer system as recited in claim 9, wherein said system information includes power management information.

11. The computer system as recited in claim 1, wherein said system interface unit and said bus interface unit are configured to communicate by sending and receiving commands across said serial communication link.

12. The computer system as recited in claim 11, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that a processor coupled to said processor bus is in a system management mode.

13. The computer system as recited in claim 11, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that a processor coupled to said processor bus is not in a system management mode.

14. The computer system as recited in claim 11, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that a processor coupled to said processor bus is in a reduced power state.

15. The computer system as recited in claim 11, wherein said commands include a command for said bus interface unit to communicate to said system interface unit to place system memory coupled to said system interface unit in a low power mode.

16. The computer system as recited in claim 11, wherein said commands include a command for said bus interface unit to communicate to said system interface unit to take system memory coupled to said system interface unit out of a low power mode.

17. The computer system as recited in claim 11, wherein said system interface unit is further configured to interface to a graphics bus and to arbitrate between memory access requests from said graphics bus and said first peripheral bus, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that arbitration between said graphics bus and said first peripheral bus is masked.

18. The computer system as recited in claim 11, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that a device coupled to said system interface unit is requesting service.

19. The computer system as recited in claim 18, wherein said command is sent by said system interface unit to said bus interface unit to initialize said serial communication link after a reset.

20. The computer system as recited in claim 11, wherein said commands include a command for said bus interface unit to communicate to said system interface unit to disable or park an arbiter.

21. The computer system as recited in claim 11, wherein said commands include a command for said bus interface unit to communicate to said system interface unit that an arbiter for said first peripheral bus is unparked.

22. The computer system as recited in claim 11, wherein said commands include a no operation command sent as a placeholder by said system interface unit or said bus interface unit when the sender has no other command to send.

23. A computer bus hierarchy, comprising:

a system interface unit configured to interface a processor bus to a first peripheral bus;

a bus interface unit configured to interface said first peripheral bus to a second peripheral bus; and

a serial communication link between said system interface unit and said bus interface unit;

said system interface unit and said bus interface unit are further configured to communicate with each other across said serial communication link.

24. The computer bus hierarchy as recited in claim 23, wherein said system interface unit and said bus interface unit are configured to communicate with each other across said serial communication link by sending commands across said serial communication link, wherein said system interface unit and bus interface unit are configured to alternate after each command between which device is sending and which device is receiving a command.

25. The computer bus hierarchy as recited in claim 23, wherein said system interface unit and said bus interface unit are configured to synchronize sending and receiving commands across said serial communication link to a common clock reference.

26. The computer bus hierarchy as recited in claim 25, wherein said common clock reference is a bus clock for said first peripheral bus.

27. The computer bus hierarchy as recited in claim 26, wherein said first peripheral bus comprises a Peripheral Component Interconnect (PCI) bus.

28. The computer bus hierarchy as recited in claim 23, wherein said system interface unit and said bus interface unit are configured to communicate with each other across said serial communication link by sending commands across said serial communication link, wherein said system interface unit and bus interface unit are configured to alternate after each command between which device is sending and which device is receiving a command, wherein neither said system interface unit nor said bus interface unit drives said serial communication link for a turnaround period after a command is sent.

29. The computer bus hierarchy as recited in claim 28, further comprising a pull-up device on said serial communication link to pull said serial communication link to a high voltage when said serial communication link is not actively driven.

30. The computer bus hierarchy as recited in claim 23, wherein said serial communication link is a single connection between one conductor on said system interface unit and one conductor on said bus interface unit.

31. The computer bus hierarchy as recited in claim 23, wherein said system interface unit and said bus interface unit are configured to communicate system information across said serial communication link.

32. The computer bus hierarchy as recited in claim 31, wherein said system information includes power management information.

33. The computer bus hierarchy as recited in claim 23, wherein said system interface unit and said bus interface unit are configured to communicate by sending and receiving commands across said serial communication link.

34. The computer bus hierarchy as recited in claim 33, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that a processor coupled to said processor bus is in a system management mode.

35. The computer bus hierarchy as recited in claim 33, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that a processor coupled to said processor bus is not in a system management mode.

36. The computer bus hierarchy as recited in claim 33, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that a processor coupled to said processor bus is in a reduced power state.

37. The computer bus hierarchy as recited in claim 33, wherein said commands include a command for said bus interface unit to communicate to said system interface unit to place system memory coupled to said system interface unit in a low power mode.

38. The computer bus hierarchy as recited in claim 33, wherein said commands include a command for said bus interface unit to communicate to said system interface unit to take system memory coupled to said system interface unit out of a low power mode.

39. The computer bus hierarchy as recited in claim 33, wherein said system interface unit is further configured to interface to a graphics bus and to arbitrate between memory access requests from said graphics bus and said first peripheral bus, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that arbitration between said graphics bus and said first peripheral bus is masked.

40. The computer bus hierarchy as recited in claim 33, wherein said commands include a command for said system interface unit to communicate to said bus interface unit that a device coupled to said system interface unit is requesting service.

41. The computer bus hierarchy as recited in claim 40, wherein said command is sent by said system interface unit to said bus interface unit to initialize said serial communication link after a reset.

42. The computer bus hierarchy as recited in claim 33, wherein said commands include a command for said bus interface unit to communicate to said system interface unit that an arbiter for said first peripheral bus is parked.

43. The computer bus hierarchy as recited in claim 33, wherein said commands include a command for said bus interface unit to communicate to said system interface unit that an arbiter for said first peripheral bus is unparked.

44. The computer system as recited in claim 33, wherein said commands include a no operation command sent as a placeholder by said system interface unit or said bus interface unit when the sender has no other command to send.

45. A method for communicating information between interface units in a computer system, the method comprising:

sending a first command from a system interface unit to a bus interface unit on a serial communication link between said system and bus interface units in the computer system;

sending a second command from said bus interface unit to said system interface unit on said serial communication link after said sending a first command; and

continuing sending commands between said system and bus interface units, wherein said system and bus interface units alternate after each command between which interface unit is receiving and which is sending a command.

46. The method as recited in claim 45, further comprising initializing said serial communication link after a reset by said system interface unit sending an initialization command to said bus interface unit.

47. The method as recited in claim 45, wherein said system interface unit interfaces a processor bus to a first peripheral bus, and said bus interface unit interfaces said first peripheral bus to a second peripheral bus.

48. The method as recited in claim 45, wherein said serial communication link is synchronized to a common clock received by said system and bus interface units.

49. The method as recited in claim 48, wherein neither said system nor said bus interface unit drives said serial communication link for one common clock period after each command is sent.

50. The method as recited in claim 45, wherein said serial communication link is a single conductor connection between said system and bus interface units.

51. The method as recited in claim 45, wherein said commands are four bits in length.

52. A method for communicating information between interface units in a computer system, the method comprising:

placing a CPU in a low power state;

sending, on a serial communication link between a system interface unit and a bus interface unit, a CPU low power command from said system interface unit to said bus interface unit, wherein said system interface unit is coupled to said CPU, wherein said CPU low power command informs said bus interface unit that said CPU is in said low power state; and

sending, on said serial communication link, a memory off command from said bus interface unit to said system interface unit to instruct said system interface unit to place system memory coupled to said system interface unit in a reduced power state.

53. The method as recited in claim 52, further comprising sending, on said serial communication link, a system management start command from said system interface unit to said bus interface unit, wherein said system management start command informs said bus interface unit that said CPU is in a system management mode.

54. The method as recited in claim 52, further comprising sending, on said serial communication link, a system management stop command from said system interface unit to said bus interface unit, wherein said system management stop command informs said bus interface unit that said CPU is out of a system management mode.

55. The method as recited in claim 52, further comprising sending, on said serial communication link, a device wakeup command from said system interface unit to said bus interface unit, wherein said device wakeup command informs said bus interface unit that a device coupled to said system interface unit is requesting service.

56. The method as recited in claim 52, further comprising sending, on said serial communication link, a memory on command from said bus interface unit to said system interface unit to instruct said first interface unit to place system memory coupled to said system interface unit in a full power state.

57. The method as recited in claim 52, further comprising sending, on said serial communication link, an arbiter parked command from said bus interface unit to said system interface unit to inform said first interface unit a bus arbiter in said second interface unit is parked.