U.S. patent application number 12/242283 was filed with the patent office on 2009-02-26 for method and system for flexible and negotiable exchange of link layer functional parameters.
Invention is credited to Victor W. Lee, Phanindra K. Mannava, Aaron T. Spink.
Application Number | 20090055555 12/242283 |
Document ID | / |
Family ID | 37949416 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090055555 |
Kind Code |
A1 |
Mannava; Phanindra K. ; et
al. |
February 26, 2009 |
METHOD AND SYSTEM FOR FLEXIBLE AND NEGOTIABLE EXCHANGE OF LINK
LAYER FUNCTIONAL PARAMETERS
Abstract
A proposal is discussed that facilitates exchanging parameters
for a link layer that allows a variable number of parameters
without changing a communication protocol. Likewise, the proposal
allows for both components connected via the link to negotiate
values for the parameters that are exchanged without a need for
external agent intervention or redundancy.
Inventors: |
Mannava; Phanindra K.;
(Folsom, CA) ; Lee; Victor W.; (San Jose, CA)
; Spink; Aaron T.; (San Francisco, CA) |
Correspondence
Address: |
INTEL/BSTZ;BLAKELY SOKOLOFF TAYLOR & ZAFMAN LLP
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Family ID: |
37949416 |
Appl. No.: |
12/242283 |
Filed: |
September 30, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11238491 |
Sep 28, 2005 |
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12242283 |
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Current U.S.
Class: |
710/8 |
Current CPC
Class: |
G06F 13/423
20130101 |
Class at
Publication: |
710/8 |
International
Class: |
G06F 3/00 20060101
G06F003/00 |
Claims
1. A method for exchanging parameters between a first agent and a
second agent comprising: connecting the first agent to the second
agent via a link interconnect that supports a layered protocol with
at least a physical layer and a link layer, wherein the first agent
and the second agent with different interface capabilities;
communicating via a parameter exchange message, the link layer of
both the first and second agent to resolve a difference of values
between the exchanged parameters by searching a pre-determined
table of exchange parameters to resolve the difference without a
need for intervention from another agent; and resolving the
difference in the value of the parameter based on the search of the
predetermined table upon observing a predetermined message and
without a need for intervention from another agent.
2. The method of claim 1 wherein the predetermined message is a
Begin Normal Operation control message that results in both agents
switching to the agreed upon value in the predetermined table.
3. A method for exchanging parameters between a first agent and a
second agent comprising: connecting the first agent to the second
agent via a link interconnect that supports a layered protocol with
at least a physical layer and a link layer, wherein the first agent
and the second agent with different interface capabilities;
communicating via a parameter exchange message, the link layer of
both the first and second agent to resolve a difference of values
between the exchanged parameters by searching a pre-determined
table of exchange parameters to resolve the difference; resolving
the difference in the value of the parameter based on the search of
the predetermined table upon observing a predetermined message; and
exchanging a variable number of parameters between the first and
second agent.
4. The method of claim 3 wherein the predetermined message is a
Begin Normal Operation control message that results in both agents
switching to the agreed upon value in the predetermined table.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/238,491 (Attorney Docket Number 42P21954) filed Sep.
28, 2005.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to I/O bus technology,
specifically, parameter exchange for a link layer.
[0004] 2. Description of the Related Art
[0005] As is well known, input/output (I/O) buses connect different
components together in a computer system. One example of an I/O bus
is a link, which is a point-to-point interconnect connecting two
components (these components can be on the same circuit board or
across two different boards). A link could be bi-directional and
consists of an out-going direction and an in-coming direction.
Likewise, the width of the link is scalable from one bit (a.k.a.
serial) to multiple bits in parallel. A single bit is transferred
from the source component via a transmitter and received at the
destination via a receiver. In the multi-bit parallel links,
multiple bits are transferred simultaneously in parallel through
multiple transmitter and receiver pairs. The signaling technology
can be single-ended or differential. One example of a link is
depicted in FIG. 1.
[0006] PCI-express and SCID links exchange physical layer operation
parameters by embedding the component value in the special training
sequences. For reference, PCI-express is discussed in "PCI-express
Base Specification Rev 1.0, Jul. 22, 2002". Each component then
examines the incoming value and compares with its outgoing value.
Based on a predetermined schedule, the two components would arrive
at a final agreed value. For example, the PCI-Express links
exchange its data rate, the number of training sequences required,
link polarity and the reset condition in its initialization phase.
However, a change in the protocol is required in order to support
parameter negotiation in the PCI-express or the SCiD physical layer
method. Furthermore, both methods only permit exchange of fixed
number of parameters with no ability to expand. .
[0007] Typically, external agents are involved for reading
capabilities of different link interfaces and setting link
operation registers.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0008] Subject matter is particularly pointed out and distinctly
claimed in the concluding portion of the specification. The claimed
subject matter, however, both as to organization and method of
operation, together with objects, features, and advantages thereof,
may best be understood by reference to the following detailed
description when read with the accompanying drawings in which:
[0009] FIG. 1 is a prior art link.
[0010] Table 1 is a list of parameters as utilized by one
embodiment of the claimed subject matter.
[0011] FIG. 2 is an example of messages as utilized by one
embodiment of the claimed subject matter.
[0012] FIG. 3 is a method of a flowchart for link layer algorithm
as utilized by one embodiment of the claimed subject matter.
[0013] FIG. 4 is a system as utilized by one embodiment of the
claimed subject matter.
[0014] FIG. 5 is a protocol architecture as utilized by one
embodiment.
[0015] FIG. 6 is a block diagram of an apparatus for a physical
interconnect utilized in accordance with the claimed subject
matter.
DETAILED DESCRIPTION OF THE INVENTION
[0016] In the following description, for purposes of explanation,
numerous details are set forth in order to provide a thorough
understanding of the present invention. However, it will be
apparent to one skilled in the art that these specific details are
not required in order to practice the present invention.
[0017] An area of current technological development relates to I/O
buses. As previously described, the existing solutions either
require external agent intervention, require protocol changes, or
fixed number of exchanged parameters.
[0018] In contrast, a method and a system are proposed that
facilitates exchanging parameters for a link layer that allows a
variable number of parameters without changing a communication
protocol. Likewise, the method and system allow for both components
connected via the link to negotiate values for the parameters that
are exchanged without a need for external agent intervention or
redundancy. As previously discussed, a need exists for exchanging
and negotiating parameters since each agent may have a different
capability for the respective link interface, in terms of
reliability support (RAS), link width, flow control, etc..
[0019] In one embodiment, a network fabric is used to communicate
among the different components on the link. This network fabric
allows for a layered protocol and may comprise either or all of: a
link layer, a protocol layer, a routing layer, a transport layer,
and a physical layer. The fabric facilitates transporting messages
from one protocol (home or caching agent) to another protocol for a
point to point network. In one embodiment, the point to point
network is depicted in connection with FIGS. 5 and 6.
[0020] Table 1 is a list of parameters as utilized by one
embodiment of the claimed subject matter. This table illustrates a
default operational state for a link. For example, a link is
initialized by powering up physical and link layers of the
components on the two ends of the link. In this embodiment, the
physical layer initialization results in a default operational
state for the link. To be able to bring a link up in default
operational state, all components at a minimum must implement one
set of values for the parameters.
[0021] The Table 1 has four columns, (reading from left to right):
Parameter, Values, Default Value for the Parameter, and Negotiable
Status. The "Values" column lists acceptable values for the listed
parameter. The "Negotiable" column indicates if a parameter value
is negotiated between the two ends. Parameters such as number of
credits and retry buffer depth and agent types are informational
parameters. Therefore, they are not negotiable. However, they do
not have to have the same values at the two ends of the link. In
one embodiment, the following is a list and definition of some of
the parameters exchanged with the proposed method and system.
However, the claimed subject matter is not limited to this list.
One skilled in the art appreciates utilizing different parameters
and could be implementation specific. [0022] 1. Interleave: The
process of preempting sending of messages from a different virtual
channel before the current message is completely sent over the
link. [0023] 2. Virtual channel: It is a logical link between the
two link layers, used to prioritize different classes of traffic
and to avoid network deadlocks. Multiple virtual channels are
mapped to a single physical channel. [0024] 3. Flow Control: Flow
control at the link layer is done using credits for each individual
virtual channel. [0025] 4. Cyclic Redundancy Check (CRC): A
polynomial based error detection scheme, e.g. 8 bit CRC involves an
8.sup.th order generator polynomial. [0026] 5. Link Level Retry:
When a link layer receives a message in error, it `informs` the
sender to retransmit that message and in the case of `go back
n`.sup.1 type protocols retransmits all subsequent messages. For
this reason the sender keeps the messages that are sent in an
`retry buffer` till an acknowledgement is received. .sup.1
Tanenbaum, Computer Networks, Second edition Prentice Hall,
Englewood Cliffs, N.J. 1989 [0027] 6. Profile: The system
parameters are grouped into different configurations based on their
values. e.g. A desktop profile, a server profile etc. [0028] 7.
Agent type: This identifies the type of agent that is connected to
the link. Examples of agent types are Memory agent, caching agent,
IO agent etc. CSI spec includes a long list of agent types.
[0029] FIG. 2 is an example of messages as utilized by one
embodiment of the claimed subject matter. In this embodiment, the
three depicted messages are used to transfer parameter values and
to handshake during acknowledgement. The messages and their use
will be discussed in further detail in connection with FIG. 3.
[0030] FIG. 3 is a method of a flowchart for link layer algorithm
as utilized by one embodiment of the claimed subject matter. Prior
to the depicted flowchart, a link between two components is in a
default operational state after completion of a physical layer
initialization. Likewise, the link layers of the two components
have synchronized and have turned on link layer error detection.
Hence, this method for a flowchart is performed after the link has
been synchronized and link layer error detection is enabled. In
this embodiment, the flowchart may be repeated as necessary.
[0031] In one embodiment, a control message is used to transfer
parameter values and to handshake during acknowledgement. In this
embodiment, three types of special control messages are used, such
as, but not limited to: `Null.Nop`, `Parameter Exchange` (PE), and
interlock messages.
[0032] Then each link layer repeats the following [0033] i) The
link layer sends a first type of control message, Null.Nop until
any product specific reset sequences that are needed before link
layer initialization are complete. For example, waiting for a
service processor to set the local node ids. [0034] ii) The link
layers exchange a second type of control message, an interlock
signal, which is `ready to init parameter exchange`. This interlock
is completed only after a link layer agent receives as well sends
`ready to init parameter exchange` message. [0035] iii) Once the
interlock is complete, the link layer will begin sending a third
type of control message, parameter exchange {PE) messages. During
the parameter exchange, if the link layer is not sending a
parameter exchange message, it sends the first type of control
message, Null.Nop. [0036] iv) If an error occurs during the
parameter exchange, the link layer agent detecting the error
reverts to sending the second type of control message for an
interlock `ready_for_init parameter exchange messages`, which will
cause both agents to re-sync at the first interlock and retry the
parameter exchange operation. [0037] v) Once a link layer agent
completes sending all the third type of control message, `PE`
messages and has not detected any errors on the received `PE`
messages, itstarts sending the second type of control message, an
interlock message, which is a `Begin normal operation` message.
This provides the second interlock between the two link layer
agents. The link layer comes out of the second interlock only after
it both sends and receives the `Begin normal operation` messages.
[0038] vi) When an agent receives the second type of control
message, an interlock message, the `Begin_normal_operation` message
it will commit the parameters that were exchanged to the active
state. For example, if both agents choose to enable 16 bit CRC
instead of 8 bit then the link layer will activate the 16 bit CRC
on the sender immediately after the `Begin_normal_operation`
message.
[0039] In one embodiment, the negotiation algorithm is as follows.
The link layer is brought up after the physical layer. As the link
layer is brought up, the default parameter states are assumed.
During the link layer parameter exchange phase, each link layer
parameter are exchanged and negotiated. For example, Parameter A
has a default value of 0. Then, when the link layer is brought up
initially, both ends of the link will have the same value (0) for
parameter A. During the parameter exchange phase, one end of the
link (for ease of explanation, it is referred to as the north-end)
would want the parameter to go to 1 and the other end (for ease of
explanation, it is referred to as the south-end) of the link would
want the value to go to 2. When each end receives the PE message
indicating a different value than what it wants (for example,
north-end receive 2 and it wants 1), the link layer logic will use
a pre-determined table to select the final parameter. (In this
example, suppose parameter A would prefer 1 over 2). Then, the
north-end will keep its value and the south end would change its
value to it. However, both ends continue to operate assuming
Parameter A=0 until both ends see the "Begin_Normal_Op message". At
that moment, both ends switch Parameter A to 1.
[0040] In one embodiment, the error handling algorithm is as
follows: If during parameter exchange, either side of the link
detected a transmission error or negotiation error (for example, if
a link agent receive a parameter value that's out of range), the
agent will send "Ready_For_Init" to reset the process. The whole
exchange phase will start over again.
[0041] FIG. 4 is a system as utilized by one embodiment of the
claimed subject matter. In particular, FIG. 4 shows a system where
processors, memory, and input/output devices are interconnected by
a number of point-to-point interfaces.
[0042] The system of FIG. 4 may also include several processors, of
which only two, processors 270, 280 are shown for clarity.
Processors 270, 280 may each include a memory controller or a local
memory controller hub (MCH) 272, 282 to connect with memory 22, 24.
The memory could be a cache memory, SRAM, and/or DRAM. In one
embodiment, processors 270, 280 may exchange data via a
point-to-point (PtP) interface 250 using PtP interface circuits
278, 288. Processors 270, 280 may each exchange data with a chipset
290 via individual PtP interfaces 252, 254 using point to point
interface circuits 276, 294, 286, 298. In one embodiment, the
processors 270 and 280 would have multiple processor cores. Chipset
290 may also exchange data with a high-performance graphics circuit
238 via a high-performance graphics interface 239.
[0043] FIG. 5 is a high level, simplified abstraction of a protocol
architecture as utilized by one embodiment. The fabric facilitates
transporting messages from one protocol (caching processor or
caching aware memory controller) to another protocol for a point to
point network. In one aspect, the figure depicts a cache coherence
protocol's abstract view of the underlying network.
[0044] FIG. 6 is a block diagram of an apparatus for a physical
interconnect utilized in accordance with the claimed subject
matter. In one aspect, the apparatus depicts a layered protocol and
may comprise either or all of: a link layer, a protocol layer, a
routing layer, a transport layer, and a physical layer for a
cache-coherent, link-based interconnect scheme for a processor,
chipset, and/or IO bridge components. For example, the physical
interconnect may be performed by each physical layer of an
integrated device. Specifically, the physical layer provides
communication between two ports over a physical interconnect
comprising two uni-directional links. Specifically, one
uni-directional link 304 from a first transmit port 350 of a first
integrated device to a first receiver port 350 of a second
integrated device. Likewise, a second uni-directional link 306 from
a first transmit port 350 of the second integrated device to a
first receiver port 350 of the first integrated device. However,
the claimed subject matter is not limited to two uni-directional
links. One skilled in the art appreciates the claimed subject
matter supports any known signaling techniques, such as,
bi-directional links, etc.
[0045] Also, the claimed subject matter depicted in the previous
Figures and Tables may be implemented in software. For example, the
software may be stored in an electronically-accessible medium that
includes any mechanism that provides (i.e., stores and/or
transmits) content (e.g., computer executable instructions) in a
form readable by an electronic device (e.g., a computer, a personal
digital assistant, a cellular telephone).For example, a
machine-accessible medium includes read only memory (ROM); random
access memory (RAM); magnetic disk storage media; optical storage
media; flash memory devices; electrical, optical, acoustical or
other form of propagated signals (e.g., carrier waves, infrared
signals, digital signals).
[0046] Although the claimed subject matter has been described with
reference to specific embodiments, this description is not meant to
be construed in a limiting sense. Various modifications of the
disclosed embodiment, as well as alternative embodiments of the
claimed subject matter, will become apparent to persons skilled in
the art upon reference to the description of the claimed subject
matter. It is contemplated, therefore, that such modifications can
be made without departing from the spirit or scope of the claimed
subject matter as defined in the appended claims.
* * * * *