linux® git software overview - nxp semiconductors · local git workflows (continued) •undoing...

External Use

TM

Linux GIT Software Overview

FTF-SDS-F0248

A P R . 2 0 1 4

Richard Schmitt

TM

External Use 1

Scope

• Learn more about the Linux GIT software repositories, source

control basics, cloning repositories, editing files and committing

changes, synchronizing repositories, and merging.

• Also, learn about Gerrit as a workflow and change review tool and

how we use it for the QorIQ SDK release process.

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External Use 2

Agenda

• Welcome

• Basic GIT Concepts

• Working with GIT

• Collaborating with GIT

• Branching and Merging

• Command Summary

• Gerrit

• Freescale Repositories

• Advanced Usage

• Questions and Answers

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External Use 3

Basic GIT Concepts

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External Use 4

Git Basic Concepts

• Git is a distributed Version Control System (VCS)

− Originally created for the Linux kernel in 2005

− As opposed to a centralized VCS, each developer has a

complete, local repository, “cloned” from an “official” remote

repository

− The “official” repository can be updated from local repositories

by “pushing” the latest state of a local repository to the

“official” repository

Typically only the “official” repository maintainers can do that

Other developers submit patches for review to the maintainers

− Developers can synchronize their local repositories with the

“official” repository, by “pulling” the latest state from the

“official” repository to the local repository

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External Use 5

Git Basic Terms

• Repository − Version control database that stores multiple revisions of a source tree

(code base) and their associated metadata

− “.git” subdirectory in the top-level directory of a source tree that is

under Git version control

• Commit

− Represents a revision of a source tree stored in the repository

− It is a “snapshot” of the whole source tree, stored in the repository

− Identified by a 160-bit unique identifier (SHA1)

A hash from the content of the snapshot

Displayed a 40-digit hexadecimal number

− A commit SHA1 can be seen as a pointer to a source tree snapshot

− Examples of Git commands that create commits:

git commit, git merge, git cherry-pick

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External Use 6

Git Basic Terms (continued)

• Commit (continued)

− Each commit points to one or more parent commits

Predecessor “snapshots” in the revision history of the source tree

− Every commit is a full snapshot of the whole project

− Git optimizes storage, will not create copies of non-modified files

(picture from “Git/Gerrit Workshop”, http://gerrit-training.scmforge.com/git-gerrit-workshop.html)

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External Use 7


• Branch

− A movable pointer (“ref” in Git terms) that points to a given commit in a

repository

Like a symbolic link that contains the SHA1 of the given commit

− The commit SHA1 pointed to by the branch represents the latest revision

of the source tree on a given line of development, represented by the chain

of predecessor commits

− There is a default branch named “master,” if no branches are created explicitly

− For a given commit to be accessible, either a branch needs to point to it, or

another commit needs to point to it in a predecessor chain (unless you know its

SHA1)

Commits that are not pointed to by any ref are eventually garbage-collected by Git

Since the last commit is not the predecessor of any other commit, a branch or tag needs

to point to it, otherwise it will get garbage-collected by Git

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External Use 8


• Branch (continued)

− A branch is implemented as a file that contains the SHA1 of a given

commit

− Example: the “master” branch is stored as file “.git/refs/heads/master”

$ cat .git/refs/heads/master

5674c0051c6086c8db46dee88f1f53fcf0c9137f

− To create a new branch do:

$ git branch <branch name>

By default, the new branch will initially point to

the same commit as the current branch

(picture from “Git/Gerrit Workshop”,

http://gerrit-training.scmforge.com/git-gerrit-workshop.html)

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External Use 9


• Current Branch

− A repository always has a current branch (except in “detached head

mode”)

− In a newly-created repository, the current branch is “master”

− To set the current branch to a different branch do “git checkout”:

$ git checkout <branch name>

− The current branch is represented by a special ref named “HEAD”

HEAD is like a symbolic link that contains the name of the current branch

To display the current branch, use the “git branch” command

− A new commit is typically created in the context of the current branch of a

repository

Every time that a new commit is created in the repository, the current branch “ref” is

moved to point to the SHA1 of the new commit

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External Use 10


• Current Branch (continued)

− When a new commit is created, the

current branch is updated to point to it

Implicitly HEAD is also moved, since it is a

“symbolic link” for the current branch

− Example of creating a new

commit, assuming that “master”

is the current branch:

Before the new commit, branch “master”

points to commit “C”

After the new commit, branch “master” points

to commit “D”

(picture from “Git/Gerrit Workshop”,

http://gerrit-training.scmforge.com/git-gerrit-workshop.html)

HEAD

HEAD

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External Use 11


• Current Branch (continued)

− Example of setting the current branch to a different branch:


git checkout bugfix15

before after

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External Use 12


• Tag

− A fixed pointer (“ref” in Git terms) that points to a given commit in a repository Once created, a tag always points to the same commit

• Working Tree − Currently “checked-out” revision of the source tree stored in a Git repository: Source tree snapshot (commit) currently extracted from the repository,

as a hierarchy of directories/files

− Side effect of the “git checkout” command: The source tree snapshot for the corresponding commit is retrieved from the

repository and overwrites the working tree

− Files can be modified, added or removed from the working tree and then a new commit can be done to create a new source tree snapshot in the repository

• Index − Staging area for working tree changes to be included in the next commit Only changes “added” to the index will be included in the next commit

− Useful to split changes to the same working tree into multiple commits (patches)

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External Use 13


• Remote

− An “alias” for the URL of a remote repository

− A remote named “origin” is created when a remote repo is cloned

− Other remotes can be add with the “git remote add” command

• Remote Branch

− A branch of the form <remote>/<branch>

• Tracking Branch

− Local branch that tracks a branch with the same name on a remote repository

− Checking out a local branch that does not exist locally but that exists in a remote, creates a tracking branch

− Used by git pull and git push to determine the branch in the remote

• Submodule

− A submodule allows you to keep a Git repository as a subdirectory of another Git repository

− A way to split a large code base into separate git repositories (submodules)

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External Use 14

Working with GIT

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External Use 15

Git Basic Repository Structure

Top-level directory of source tree

Source files and subdirectories (working tree)

.git subdirectory (actual repository) 24K .git/refs/heads

12K .git/refs/tags

36K .git/refs/remotes/origin

5.0M .git/objects

1.5G .git/modules

Linux kernel submodule 738M .git/modules/linux

32K .git/modules/linux/refs/heads

8.0K .git/modules/linux/refs/tags

40K .git/modules/linux/refs/remotes/origin

713M .git/modules/linux/objects

U-boot submodule 64M .git/modules/u-boot

8.0K .git/modules/u-boot/refs/heads

8.0K .git/modules/u-boot/refs/tags

20K .git/modules/u-boot/refs/remotes/origin

63M .git/modules/u-boot/objects

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External Use 16

How to Create a Git Repository

• Create a local Git repository by cloning an “official” remote

repository

$ git clone <remote Git repository URL>

− Examples: $ git clone git://git.am.freescale.net/gitolite/sdk/linux-devel.git

$ git clone ssh://gerrit.am.freescale.net/sdk/sdk-devel.git

• Create a stand-alone local Git repository in the current directory

− $ git init

• Create a “bare” Git repository (a repository without a working tree)

in a Git server

− $ git clone ––bare <URL of existing repository>

− $ git init --bare

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External Use 17

Local Git Workflows

• A workflow to modify existing files in a local repository

− Checkout target branch

$ git checkout

− Edit existing files

− Stage the changes

$ git add <files changed>

− Review your changes

$ git diff –staged HEAD

− Commit the changes

$ git commit

(Picture from “Pro Git”, by Scott Chacon

http://git-scm.com/book)

Index

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External Use 18

Local Git Workflows (continued)

• A workflow to modify existing files in a local repository, without

explicit staging


$ git checkout

− Edit existing files

− Review your changes

$ git diff HEAD

− Commit all unstaged changes

(not including new files)

$ git commit -a



Automatic staging

done as part of

“git commit –a”

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External Use 19


• A workflow to create new files in a local repository


$ git checkout

− Create new files

− Add new files to index

$ git add <new files>


$ git commit



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External Use 20


• A workflow to remove or rename

existing files in a local repository


$ git checkout

− Remove files from working tree

and index

$ git rm <files>

− Rename files in working tree and

index

$ git mv <files>


$ git commit



TM

External Use 21


• Undoing uncommitted changes

− Undoing all uncommitted changes from working tree and from index

$ git reset –hard HEAD

Resets both the working tree and the index to match the source tree snapshot of the commit pointed to by the current branch (branch pointed to by HEAD)

− Undoing uncommitted changes to a specific file

$ git checkout <file path>

Restore file in the working tree and index from the source tree snapshot of the

commit pointed to by the current branch

− Switch to another branch discarding all uncommitted changes for the

current branch

$ git checkout –force <branch name>

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External Use 22


• Undoing committed changes

− Undoing the last commit

$ git reset –hard HEAD^

Resets both the working tree and the index to match the source tree snapshot of the predecessor commit for the commit pointed to by the current branch

− Undoing the last n commits

$ git reset –hard HEAD~n

− Reverting a given commit in the middle of the predecessor chain for the

current branch

$ git revert <commit SHA1>

Creates a new commit on the current branch that reverses the effect of the

given commit

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External Use 23

Collaborating with GIT

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External Use 24

Git server host

Git Distributed Model

• Developers have their own local repositories cloned from an “official”

remote repository

“Official” Git

Repository

“Local” Git

Repository

“Local” Git

Repository

git clone,

git fetch,

git pull

git clone,

git fetch,

git pull

..

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External Use 25

Git server host

Git Distributed Model (continued)

• Repository maintainers can update the “official” repository from

their local repositories

“Official” Git

Repository

“Local” Git

Repository

“Local” Git

Repository

git push

git push

..

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External Use 26

Distributed Git Workflows

• Cloning a remote repository $ git clone git://git.am.freescale.net/gitolite/sdk/linux-devel.git

− Locally the remote repo will be known as the remote alias “origin”

− Local branch “master” is a tracking branch


Local branch

associated with a

branch of same

name on the remote

TM

External Use 27

Distributed Git Workflows (continued)

• Creating a new tracking branch $ git checkout <branch name from remote>


Local branch

associated with a

branch of same

name on the remote

release1.0

git checkout release1.0

HEAD

Pointer to current

branch changed

TM

External Use 28


• Fetching a remote repository (previously cloned) $ git fetch origin release1.0

− Remote branch “origin/release1.0” in the local repo is updated to match branch

“release1.0” in the remote “origin” repo


Local branch

“release1.0”

is not changed

release1.0 HEAD

after fetch

before fetch

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External Use 29


• Pulling from a remote repository (previously cloned) $ git pull origin release1.0

− Same as fetch but also, remote branch “origin/release1.0” is merged into local

branch “release1.0”


after merge

(“fast forward” merge

in this case)

release1.0 HEAD

Pull = fetch + merge

after fetch

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External Use 30


• Pushing to a remote repository (previously cloned)

− Example: Push the local branch “feature” to branch “master” in the

remote “origin”

$ git push origin feature:master

or

$ git push origin HEAD:master


NOTE:

without “<source branch>:”

local branch “master” would be

pushed instead

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External Use 31

Branching

TM

External Use 32

Local Git Workflows with Multiple Branches

• Git merge – Case 1: fast-forward merge

− Example: Merge branch “feature1” to branch “master”

$ git checkout master

$ git merge feature1


before after

git merge

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External Use 33

Local Git Workflows with Multiple Branches (continued)

• Git merge – Case 2: actual merge of two commit chains

− Example: Merge branch “feature1” to branch “master”


$ git merge feature1


git merge

before

after with merge

conflicts resolved,

if any

TM

External Use 34


• Git rebase: re-apply commits from “feature 1” since common

ancestor, on top of commit pointed to by “master”

$ git checkout feature1

$ git rebase master

before

This now

unreferenced

commit chain will

get garbage

collected

with merge

conflicts resolved,

if any

git rebase


after

Rebase “feature1”

from “master”

TM

External Use 35


• Git cherry-pick

− Example: Apply commit F on branch “master”


$ git cherry-pick <commit F>

before


after

git cherry-pick

G points to the

same source tree

snapshot as F, but

has different

ancestor

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External Use 36

GIT Command Summary

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External Use 37

Commonly Used Commands

• git clone from the upstream to prime your local repository

• git pull and git fetch from "origin" to keep up-to-date with the

upstream

• git push to shared repository, if you adopt CVS style shared

repository workflow

• git branch (with no arguments) to see where you are

• git log to see what happened

• git whatchanged to find out where things have come from

• git checkout to switch branches (and create local tracking

branches)

• git add to stage changes and to add new files

• git remote to see the existing remotes for the local repo

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External Use 38

Commonly Used Commands (continued)

• git diff to see differences

• git status to see current state of working tree and index

• git commit to advance the current branch

• git reset and git checkout <pathname> to undo changes.

• git rebase to maintain topic branches

• git tag to mark known point

• git merge to merge another branch into the current branch

• git branch <branch name> to create a new branch starting at the

last commit on the current branch

• git cherry-pick to create a new commit on the current branch, that

duplicates a commit from another branch

• git revert to create a new commit that reverses the change from an

earlier commit on the current branch

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External Use 39

Gerrit

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External Use 40

Gerrit Basic Concepts

• Gerrit is Web-based code review

system integrated with Git

− It serves as front-end to “official”

(authoritative) Git repositories

− Developers can only push “for review”

− Only designated maintainers can push

to the “official” repositories

• It is also integrated with the Jenkins

continuous-integration tool

− It automatically builds each change

submitted for review

(picture from “Gerrit Code Review - A Quick Introduction”,

http://gerrit-documentation.googlecode.com/svn/Documentation/2.7/intro-quick.html)

TM

External Use 41

Gerrit Workflow


Second and

further iterations of

the same change

must include the

Gerrit change Id of

the change

TM

External Use 42

Initial Push for Code Review

$ git commit

$ git push origin HEAD:refs/for/master


Each iteration of a Gerrit

change consists of a

Gerrit “patch set,”

which corresponds to a

single Git commit A Gerrit “patch

set” is represented

by a Git branch

(commit pointer)

Remote “origin” repo in

Gerrit server

Gerrit change #

Iteration #

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External Use 43

Subsequent Push for Code Review

$ git commit –amend



Really

git –amend + Gerrit magic

(change-Id commit-msg hook)

On the remote, after push,

commit D will be pointed to by:

refs/changes/35/135/2

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External Use 44

Gerrit Change Web Page


Gerrit change #

Jenkins

build

succeeded

Gerrit change Id

All Git commits

(“patch sets”) that

are iterations of the

same Gerrit change

must have the same

change Id in the

commit message

TM

External Use 45

Push Multiple Changes



Remote “origin” repo in

Gerrit server

• For each commit

from the local branch

not available in the

remote branch, a

different Gerrit

change gets created

• All these changes

are chained together

in a “depends on”

chain

TM

External Use 46

Working with Freescale Repositories

TM

External Use 47

Freescale SDK Git Repositories

• Public repositories

− Linux kernel repository

http://git.freescale.com/git/cgit.cgi/ppc/sdk/linux.git

− U-boot repository

http://git.freescale.com/git/cgit.cgi/ppc/sdk/u-boot.git/

− For other repositories see

http://git.freescale.com

• Internal repositories

− Linux kernel repository

http://git.am.freescale.net/gitolite/gitweb.cgi/sdk/linux-devel.git

− U-boot repository

http://git.freescale.com/git/cgit.cgi/ppc/sdk/u-boot.git

− For other repositories see

http://git.am.freescale.net

http://git.freescale.com/git/cgit.cgi/ppc/sdk/linux.git




http://git.freescale.com/







http://git.am.freescale.net/

TM

External Use 48

Gerrit for Freescale SDK Repositories

• Gerrit Web page for internal SDK repositories

http://git.am.freescale.net

• Gerrit Web page for changes submitted for review

http://git.am.freescale.net:8181

• Jenkins Web page for Gerrit-triggered builds

http://busy.am.freescale.net/me/my-views/view/All/job/gerrit-linux-build-

for-submit

http://git.am.freescale.net/

http://git.am.freescale.net:8181/

http://busy.am.freescale.net/me/my-views/view/All/job/gerrit-linux-build-for-submit











TM

External Use 49

Example of Tracking Down a Build Break

• Given the following Linux kernel build error: arch/powerpc/kernel/built-in.o: In function `setup_pw20_idle': (.text+0xb364): undefined reference to `.has_pw20_altivec_idle' arch/powerpc/kernel/built-in.o: In function `setup_altivec_idle': (.text+0xb390): undefined reference to `.has_pw20_altivec_idle' make[1]: *** [vmlinux] Error 1 …

• Find the commit that introduced the error $ git log -S "has_pw20_altivec_idle"

commit cf41f28c197342f10da49d5b71dec498b3434bc5

Author: Wang Dongsheng <[email protected]>

Date: Thu Sep 12 10:24:55 2013 +0800

powerpc/85xx: fix pw20&altivec idle can not work after cpuhotplug restore PW20 & AltiVec idle should be enabled, when the cpuhotplug restore. Signed-off-by: Wang Dongsheng <[email protected]> Change-Id: Ib4d2ac24eedde0a6a814f3b5f0b42ca03e20494c Reviewed-on: http://git.am.freescale.net:8181/4269

…

Gerrit change #

Gerrit change Id

Git commit SHA1

mailto:[email protected]

mailto:[email protected]

http://git.am.freescale.net:8181/4269

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External Use 50

Advanced Usage

TM

External Use 51

Example of Tracking Down a Build Break

• See what files got changed by the commit: $ git show --name-status cf41f28c197342f10da49d5b71dec498b3434bc5

commit cf41f28c197342f10da49d5b71dec498b3434bc5

…

M arch/powerpc/include/asm/reg_booke.h

M arch/powerpc/kernel/cpu_setup_fsl_booke.S

M arch/powerpc/platforms/85xx/common.c

• Examine the specific changes: $ git diff cf41f28c197342f10da49d5b71dec498b3434bc5 \

cf41f28c197342f10da49d5b71dec498b3434bc5^

TM

External Use 52

Example of Tracking Down a Build Break (continued)

• Confirm the culprit lines and who changed

them: $ git blame arch/powerpc/kernel/cpu_setup_fsl_booke.S

...

cf41f28c (Wang Dongsheng 2013-09-12 …) _GLOBAL(setup_pw20_idle)

cf41f28c (Wang Dongsheng 2013-09-12 …) mflr r10

cf41f28c (Wang Dongsheng 2013-09-12 …) bl .has_pw20_altivec_idle

cf41f28c (Wang Dongsheng 2013-09-12 …) mtlr r10

cf41f28c (Wang Dongsheng 2013-09-12 …) cmpwi r3, 0

cf41f28c (Wang Dongsheng 2013-09-12 …) beq 2f

...

TM

External Use 53

Example of Tracking Down a Build Break (continued)

• On what branches is this commit (in their

predecessor commit chains)? $ git branch --contains cf41f28c197342f10da49d5b71dec498b3434bc5

b4860rev2

master

sdk-kernel-3.8

sdk-v1.4.x

• On which branch was this commit originally

created? $ git-what-branch.pl --all cf41f28c197342f10da49d5b71dec498b3434bc5

b4860rev2

…

(script available at https://github.com/SethRobertson/git-what-branch)

https://github.com/SethRobertson/git-what-branch





TM

External Use 54

References

• http://git-scm.com/book

• http://gerrit-training.scmforge.com/git-gerrit-workshop.html

• http://www.kernel.org/pub/software/scm/git/docs

• https://www.kernel.org/pub/software/scm/git/docs/user-manual.html

• https://review.typo3.org/Documentation/intro-quick.htm

• http://gerrit-

documentation.googlecode.com/svn/Documentation/2.7/intro-

quick.html l

http://git-scm.com/book



http://gerrit-training.scmforge.com/git-gerrit-workshop.html







http://www.kernel.org/pub/software/scm/git/docs

https://www.kernel.org/pub/software/scm/git/docs/user-manual.html



https://review.typo3.org/Documentation/intro-quick.html









TM

External Use 55

Introducing The

QorIQ LS2 Family

Breakthrough,

software-defined

approach to advance

the world’s new

virtualized networks

New, high-performance architecture built with ease-of-use in mind Groundbreaking, flexible architecture that abstracts hardware complexity and

enables customers to focus their resources on innovation at the application level

Optimized for software-defined networking applications Balanced integration of CPU performance with network I/O and C-programmable

datapath acceleration that is right-sized (power/performance/cost) to deliver

advanced SoC technology for the SDN era

Extending the industry’s broadest portfolio of 64-bit multicore SoCs Built on the ARM® Cortex®-A57 architecture with integrated L2 switch enabling

interconnect and peripherals to provide a complete system-on-chip solution

TM

External Use 56

QorIQ LS2 Family Key Features

Unprecedented performance and

ease of use for smarter, more

capable networks

High performance cores with leading

interconnect and memory bandwidth

• 8x ARM Cortex-A57 cores, 2.0GHz, 4MB L2

cache, w Neon SIMD

• 1MB L3 platform cache w/ECC

• 2x 64b DDR4 up to 2.4GT/s

A high performance datapath designed

with software developers in mind

• New datapath hardware and abstracted

acceleration that is called via standard Linux

objects

• 40 Gbps Packet processing performance with

20Gbps acceleration (crypto, Pattern

Match/RegEx, Data Compression)

• Management complex provides all

init/setup/teardown tasks

Leading network I/O integration

• 8x1/10GbE + 8x1G, MACSec on up to 4x 1/10GbE

• Integrated L2 switching capability for cost savings

• 4 PCIe Gen3 controllers, 1 with SR-IOV support

• 2 x SATA 3.0, 2 x USB 3.0 with PHY

SDN/NFV

Switching

Data

Center

Wireless

Access

TM

External Use 57

See the LS2 Family First in the Tech Lab!

4 new demos built on QorIQ LS2 processors:

Performance Analysis Made Easy

Leave the Packet Processing To Us

Combining Ease of Use with Performance

Tools for Every Step of Your Design

TM

© 2014 Freescale Semiconductor, Inc. | External Use

www.Freescale.com

http://www.freescale.com/

https://twitter.com/Freescale

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linux® git software overview - nxp semiconductors · local git workflows (continued) •undoing...

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